I/O vs. Outboard--Which is most reliable?
Harry Krause
mar...@ix.netcom.com (Lost in Space) write:
When comparing an outboard vs and I/O:
1. Which is the most reliable?
2. Which is the least expensive to maintain?
3. Which as the propensity to last longer?
What a can of worms!
My feeling is that given engines of similar size on similar boat given decent
care:
* the outboard engine is the most reliable, in that it is designed from the
beginning (except for Honda) to be a marine engine. It does far better at high
RPMs than the typical car engine used in an I/O. Now, there are I/O's that use
specially built engines put together for the rigors of marine life or for high
output...these are stronger than the typical I/O engine.
* car engines in boats are cheaper to fix than outboard motors. Almost any car
mechanic can fix an I/O engine.
* outboards last a lot longer than I/O engine. This newsgroup is full of guys
with outboards that are 30-40 years old and are still running. Rarely do you
read about a really ancient I/O.
* two weak links on an I/O
the drive portion from the engine to the propellor. much more
troublesome than the lower unit of an outboard,
not as resistant to salt water and corrosion as an outboard.
Marcus G Bell
Harry Krause (hkr...@gate.net) wrote:
> * the outboard engine is the most reliable, in that it is designed
> from the beginning (except for Honda) to be a marine engine. It does
> far better at high RPMs than the typical car engine used in an
> I/O. Now, there are I/O's that use specially built engines put
> together for the rigors of marine life or for high output...these
> are stronger than the typical I/O engine.
Yes, the outboard is designed to sustain near-full output for much
longer than the converted car engine I/O.
Some I/O engines begin life as a truck engine. A truck spends
something like half its operating life pulling uphill and/or into the
wind, with a heavy load. An I/O will still outdo the truck in the
stress it puts on the engine, but car engines have it easiest at some
20 HP actual power output for much of the time.
Now about the Honda 4-stroke outboard. It is my understanding from
discussing it with dealers that the 90 and 130 HP models share some
internal components with the auto engines, like pistons, but that the
block was designed from the ground up to be an outboard. Note that the
auto engine mates to the transmission at the flywheel, but that the
outboard mates to the lower unit at the side opposite the
flywheel. Also, flow of coolant needs to take gravity into
consideration, and the flow scheme in the horizontal auto engine is
ill-suited to the vertical configuration. The smaller Honda outboards
have nothing in common with their automotice contemporaries, but I
suppose there's a chance some internals could have come from the
motorcycle end of things.
The only marinized auto engines that were used in outboards of which I
am aware are the Crosley, used in Fageol, Homelite, and Bearcat 40-55
HP outboards, and the Coventry Climax used in Bearcat 85 HP outboards.
--
--
Marcus. ( be...@mail.med.upenn.edu )
Bud Kuenzli
A response from somebody with some depth of knowledge....very nice. So in
the dockside conversation mode, describe your own pick for a good river
boat for use on large rivers as in Yukon large, and shallow rivers, as in
Yukon flats (some very shallow areas). What kind, make, model engine are
you getting to take you and three buddies out hunting for moose. In jet
models (as opposed to props), have any recommendations ?
In article <6js72e$cfp$1...@netnews.upenn.edu>, be...@mail.med.upenn.edu
(Marcus G Bell) wrote:
> Harry Krause (hkr...@gate.net) wrote:
>
> > * the outboard engine is the most reliable, in that it is designed
> > from the beginning (except for Honda) to be a marine engine. It does
> > far better at high RPMs than the typical car engine used in an
> > I/O. Now, there are I/O's that use specially built engines put
> > together for the rigors of marine life or for high output...these
> > are stronger than the typical I/O engine.
snip
K Smith
Harry & Marcus,
Which is most reliable? I guess it's personal opinion.
I would like to point out that motors in preasure craft don't work all that hard,
they rev. sure (good coolant flow, good oil flow/pressure, proper operating temp, not too
many cold starts per total engine hour of operation etc. etc.) but reving is no problem in
itself, they don't see too many high torque loads applied.
The graphed power curve on most pleasure craft engines, particularly two strokes,
is a convex (i.e. the max torque occurs about 2/3 to 3/4 of max rpm., but the graphed
power consumption curve of a fixed pitch propeller is a concave. (i.e. the torque required
to increase revs increases exponentially, the prop will consume alot more than double the
torque to double it's revs.)
The practical outcome of this is that props are pitched to consume the engines
max. power at usually max. revs & as soon as the user reduces power, the torque required
drops much faster than the revs, so that at 2/3 to 3/4 of max revs (most peoples long term
cruise) the engine is loafing. (you can't help but see this in your throttle settings,
that last 1/4 of the revs takes 1/2 the throttle) The only time the engine in a pleasure
craft really works is upon acceleration or max power, few users run constantly/long at max
& as a percentage of use there is not much really hard acceleration. (unless you're trying
to get me to ski)
What kills engines is load, not revs things like high/full throttle pulling up a
long hill with low engine revs, which is something a prop can never subject an engine to,
(relative to the engines max. rpm high load with low revs equals poor coolant flow, below
max. oil pressure, high piston thrust loads, more blowby & higher detonation risk).
Obviously numerous cold starts are bad & motor vehicles/trucks have many more.
Cummins give an excellent 3yr warranty on their marine engines when used
commercially, something I thought was pretty brave, until I realised the warranty is
conditional upon their tech. actually confirming after installation that the engine is not
"over-propped" & can easily attain max revs. These marine engines last longer than their
brothers in heavy trucks which are repeatedly having a load applied which, despite modern
multispeed transmissions, the engine cannot overcome.
Most pleasure craft engines don't "wear" out they suffer corrosion, ancillary or
drive problems long before the crank, bore/pistons, valves "wear" out.
Karen Smith.
On 19 May 1998 15:04:46 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
>Harry Krause (hkr...@gate.net) wrote:
>
>> * the outboard engine is the most reliable, in that it is designed
>
>Yes, the outboard is designed to sustain near-full output for much
>longer than the converted car engine I/O.
>
>Some I/O engines begin life as a truck engine. A truck spends
>something like half its operating life pulling uphill and/or into the
>wind, with a heavy load. An I/O will still outdo the truck in the
>stress it puts on the engine, but car engines have it easiest at some
>20 HP actual power output for much of the time.
>
>
Harry Krause
Sorry, I don't know those waters and I also don't know anything about those kind
of river jets.
Bud Kuenzli wrote:
>
> A response from somebody with some depth of knowledge....very nice. So in
> the dockside conversation mode, describe your own pick for a good river
> boat for use on large rivers as in Yukon large, and shallow rivers, as in
> Yukon flats (some very shallow areas). What kind, make, model engine are
> you getting to take you and three buddies out hunting for moose. In jet
> models (as opposed to props), have any recommendations ?
>
> In article <6js72e$cfp$1...@netnews.upenn.edu>, be...@mail.med.upenn.edu
> (Marcus G Bell) wrote:
>
> > Harry Krause (hkr...@gate.net) wrote:
> >
> > > * the outboard engine is the most reliable, in that it is designed
Gould 0738
Karen Smith wrote:> The graphed power curve on most pleasure craft engines,
At the risk of coming across as politically incorrect and an incorrigible MCP,
this post shows a degree of mechanical insight which is unusual among the
gender normally named "Karen". Pretty impressive for a "girl" :) (pretty
impressive for anybody, really).
'cuse me now, gotta go get my asbestos flame proof suit on :)
K Smith
Gould?
Just looking down the jumper here, a bit further these days I'll admit, but yep
definitely; I'm a "Karen".
Karen Smith.
WaveRide N
Boy Karen you're a boating guys DREAM! A women that not only likes
boats but can diagnose and fix em' when things break. WOW What a WOMEN!! :)
I'd love to be able to come home from a fun day of burning lots of fuel & say
Honey
454mag doesn't run right can you look at it? PLEASE…. <g>
Seriously though you seem very knowledgeable & make a great contribution to
the
group Thanks & keep up the good work.
Enjoy,
Wave
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> Harry & Marcus,
> Which is most reliable? I guess it's personal opinion.
Karen,
I appreciate the detail you've gone into here.
As far as looking down at some long jumper cables to see whether
you're qualified to talk about this stuff, or whatever you and the
others have been talking about, let's just say that like that of some
others on this group (I don't include myself), your clear grasp of the
material speaks for itself.
I have some questions to discuss, in the hope that I might learn
something.
> I would like to point out that motors in preasure craft don't
> work all that hard, they rev. sure (good coolant flow, good oil
> flow/pressure, proper operating temp, not too many cold starts per
> total engine hour of operation etc. etc.) but reving is no problem
> in itself, they don't see too many high torque loads applied.
> The graphed power curve on most pleasure craft engines,
> particularly two strokes, is a convex (i.e. the max torque occurs
> about 2/3 to 3/4 of max rpm., but the graphed power consumption
> curve of a fixed pitch propeller is a concave. (i.e. the torque
> required to increase revs increases exponentially, the prop will
> consume alot more than double the torque to double it's revs.)
> The practical outcome of this is that props are pitched to
> consume the engines max. power at usually max. revs & as soon as the
> user reduces power, the torque required drops much faster than the
> revs, so that at 2/3 to 3/4 of max revs (most peoples long term
> cruise) the engine is loafing. (you can't help but see this in your
> throttle settings, that last 1/4 of the revs takes 1/2 the throttle)
> The only time the engine in a pleasure craft really works is upon
> acceleration or max power, few users run constantly/long at max & as
> a percentage of use there is not much really hard acceleration.
> (unless you're trying to get me to ski)
Below speeds of cavitation or other inefficiencies, the power
consumed by the prop is proportional to the power required to move the
boat. The power to move the boat on plane goes as velocity squared. On
plane, the boat speed is roughly proportional to engine RPM. This
means that power to the prop must go as RPM squared, i.e. to the power
of 2, the exponential you have refered to.
If I run at 71% of max rated RPM, (as long as I'm still planing) I'm
doing 71% of the max boat speed. This is a good cruising speed, to the
lower end of the 2/3-3/4 you gave above. This means that the power to
the prop is 71% x 71% of max, or 50%. Half power, but more than half
speed. Great, save fuel and all that.
Now let's look at torque. Regardless of the measured full-throttle
torque curve of the engine, if I know the power to the prop and the
engine RPM, I know the torque as well, under the present operating
conditions. Power = Torque x RPM. To achieve 1/2 power at 71% RPM, I
need 71% of the torque which is available at max RPM. Since max RPM is
usually set past where the torque curve peaks but hasn't fallen that
far, that means I'm calling for roughly 71% of max torque.
Car engines work mostly around 10-20% of their rated HP, give or
take. I would bet it's the exceptional car engine which is loaded to
50% of max HP and 70% of max torque for any appreciable duration. I
may be more shaky in talking about truck engines, but these seem high
for even a truck. I would definitely not consider these figures to be
"loafing".
(I should point out that when I spoke of "truck engine" now and in
earlier posts, I was meaning light trucks.)
> What kills engines is load, not revs things like high/full
> throttle pulling up a long hill with low engine revs, which is
> something a prop can never subject an engine to, (relative to the
> engines max. rpm high load with low revs equals poor coolant flow,
> below max. oil pressure, high piston thrust loads, more blowby &
> higher detonation risk). Obviously numerous cold starts are bad &
> motor vehicles/trucks have many more.
Can't disagree too much here. Though RPMs "load" an engine in certain
ways too. Clearly, we must let no parameter run at close to max :-)
Running a gas engine WOT at submaximal RPM is more fuel-efficient than
at lower throttle but higher RPMs in a lower gear. Lower pumping
losses, as in a diesel. This could partly explain the tall gearing on
the land vehicles.
> Cummins give an excellent 3yr warranty on their marine engines
> when used commercially, something I thought was pretty brave, until
> I realised the warranty is conditional upon their tech. actually
> confirming after installation that the engine is not "over-propped"
> & can easily attain max revs. These marine engines last longer than
> their brothers in heavy trucks which are repeatedly having a load
> applied which, despite modern multispeed transmissions, the engine
> cannot overcome.
I'd have to agree that between a commercial truck and a commercial
boat, the boat engine sees the easier life. But here I believe we're
talking about bigger engines and inboards, not I/O engines, but you'll
correct me if I'm mistaken. I think in general the I/O engine works
harder than its land-locked counterpart.
> Most pleasure craft engines don't "wear" out they suffer
> corrosion, ancillary or drive problems long before the crank,
> bore/pistons, valves "wear" out.
Amen.
K Smith
Marcus,
Yes I would agree.
Karen Smith.
Marcus G Bell
> K Smith (drif...@nospamwebrider.net.au) wrote:
> > The graphed power curve on most pleasure craft engines,
> > particularly two strokes, is a convex (i.e. the max torque occurs
> > about 2/3 to 3/4 of max rpm., but the graphed power consumption
> > curve of a fixed pitch propeller is a concave. (i.e. the torque
> > required to increase revs increases exponentially, the prop will
> > consume alot more than double the torque to double it's revs.)
Marcus G Bell (be...@mail.med.upenn.edu) wrote:
> Below speeds of cavitation or other inefficiencies, the power
> consumed by the prop is proportional to the power required to move the
> boat. The power to move the boat on plane goes as velocity squared. On
> plane, the boat speed is roughly proportional to engine RPM. This
> means that power to the prop must go as RPM squared, i.e. to the power
> of 2, the exponential you have refered to.
Karen,
Upon further thought, it would seem that you used the term "torque"
where you may have meant "power".
Power increases exponentially with boat speed, roughly as speed
squared. Since RPM tracks boat speed, and since Power = RPM x Torque,
speed, torque and RPM rise linearly together and proportional to the
square root of engine power.
This means that when you said
"the torque required to increase revs increases exponentially, the
prop will consume alot more than double the torque to double it's
revs"
did you mean to say
"the *power* required to increase revs increases exponentially, the
prop will consume alot more than double the *power* to double it's
revs"
??
Just curious.
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> Marcus,
> Yes I would agree.
We agree that the I/O engine gets a workout, as originally said?
This other stuff about comparing the commercial truck engines to
commercial inboards was great. I hope we get lots more like it.
K Smith
Marcus,
No I meant torque, you'll note I was talking about the power curve, being the
power the engine can generate at various revs. against the power curve of the propeller,
being the power consumed by the propeller at various revs. (power being an amalgam of
torque & revs)
Torque & revs are the of power, so what I was saying was that the torque consumed
by the propeller drops much quicker than the revs. & yes it could be expressed as the
total power required drops, but what I was trying to accentuate was not the obvious that
the prop requires less power to turn slower, but that it required alot less torque than
the engine was capable of making at any revs lower than max. (assumming the prop is
pitched correctly to match max. revs.)
So to maintain say 3/4 revs only requires say 1/2 throttle, because at 3/4 revs
most engines are at their max. torque range, provided the throttle is opened & a load
applied to consume that load, that being the essence of my argument that the prop is
incapable of applying a load that the engine will need any real throttle to overcome.
(other than max. & near max.)
I liken it to a car at high speed cruise in flat country, maybe very high speed
but that of itself is not a problem to the longevity of the engine. (most modern cars, for
pollution, noise & economy reasons are incapable of max revs. in top gear on flat road)
Your comments about power required to plane, then the greatly reduced amount of
power required to cruise once on the plane are I guess true, but not relevant to what I
was saying, which remains true of a heavy displacement vessel as a planing type.
Karen Smith.
On 27 May 1998 05:12:12 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
>
>> K Smith (drif...@nospamwebrider.net.au) wrote:
>
>> > The graphed power curve on most pleasure craft engines,
>> > particularly two strokes, is a convex (i.e. the max torque occurs
>> > about 2/3 to 3/4 of max rpm., but the graphed power consumption
>> > curve of a fixed pitch propeller is a concave. (i.e. the torque
>> > required to increase revs increases exponentially, the prop will
>> > consume alot more than double the torque to double it's revs.)
>
>
>Marcus G Bell (be...@mail.med.upenn.edu) wrote:
>
>> Below speeds of cavitation or other inefficiencies, the power
>> consumed by the prop is proportional to the power required to move the
>> boat. The power to move the boat on plane goes as velocity squared. On
>> plane, the boat speed is roughly proportional to engine RPM. This
>> means that power to the prop must go as RPM squared, i.e. to the power
>> of 2, the exponential you have refered to.
>
>Karen,
>
>Upon further thought, it would seem that you used the term "torque"
>where you may have meant "power".
>
>Power increases exponentially with boat speed, roughly as speed
>squared. Since RPM tracks boat speed, and since Power = RPM x Torque,
>speed, torque and RPM rise linearly together and proportional to the
>square root of engine power.
>
>This means that when you said
>
> "the torque required to increase revs increases exponentially, the
>prop will consume alot more than double the torque to double it's
>revs"
>
>did you mean to say
>
> "the *power* required to increase revs increases exponentially, the
>prop will consume alot more than double the *power* to double it's
>revs"
>
>??
>
>Just curious.
>
K Smith
Marcus,
Well yes & no. Yes; a converted car engine hooked onto a fixed pitch propeller
does "get a workout" but no; not so it is bad for it or will effect it's reliability as
per Harry's original post.
As I've said, revs. don't bother an engine so long as it is within the OEM limit.
It's load that kills.
The "problem" as I see it in car engines being used in boats (mercruiser, volvo
etc,) is the so called conversion, not the power required of the motor.
Most are raw water cooled, which is a disaster, the consequences are;
(i) The oil never gets to proper temp. & degrades/contaminates much quicker than in an
auto, it's like a constant run at partial warmup,
(ii) The oil additives are designed to reduce carbon build up in the top of the engine,
rings & valves especially, constant mid temp (150-160f) operation allows much quicker
deposit build up. (I guess you can see why I have a thing about your pal Ralph)
(iii) Modern engines like Chev. use very light ring pressures (that's one of the reasons
they last much better these days) & rely heavily on combustion pressure behind the rings
to seal, obviously any premature carbon build up in the ring lands stops their proper
operation/sealing & then the blowby compounds the problem quickly.
(iii) The engines corrode, but this is not "rust" in the conventional sense (whilst hot
salt water is extremely corrosive) it is cavitation, the combustion, (explosions if you
like) set up shock waves through the bore (some say the bore actually flexes, I don't but
some do) the shock waves go into the coolant which sees a high frequency alternating high
& low pressure. Just like a cavitating prop the imploding bubbles so created actually
erode the metal of the bore, block, head whatever, that is why raw water cooled engines
usually suffer pin hole corrosion (usually at 90 deg. to wrist pin, why there?) much more
than the same coolant cooled auto engine. The "inhibitors" in modern auto engines, coat
the water jacket with a protective coating, which also succumbs to erosion by the
cavitation but so long as it is changed regularly it will self repair & protect the
underlying metal. Further the "pressure cap" subjects the cooling system to pressure, one
reason being to increase the boiling point of the coolant, but the main reason is to
suppress cavitation/erosion.
(iv) So fresh or saltwater, raw water cooling is a big no no.
The outcome of all this is that the I/Os don't last as long as they should,
usually the bore/pistons give up, not through "wear" because they're worked hard, (because
I say they aren't) but because of the oil degading & not keeping the pistons/rings clean,
to a lesser extent the same happens to the valves, sludge builds up because the oil
dispersants can't keep the contaminants in suspension etc. etc.
Now if all car engines were properly converted, with heat exchangers & in most
cases proper oil coolers, most of these problems would go away & I think they would at
least match if not beat their auto brothers for longevity. I know the closed cooling is an
"option" but it is priced such that you are perilously close to the same pricing as a
proper marine diesel, then why not get a proper gearbox/drive & so on & so on.
These things are essentially designed for the rec. boater, down to a price with
high retail margins built in, to support small seasonal dealers, like alot of other
hobbies. sporting equip, & other optional expenditure. (Harry saved $2000 in 6,800 & I
guess the dealer was still happy with the deal)
I guess I sound critical of the I/O but the good news is everything I say is wrong
with them applies equally to O/Bs, hence I said it's "opinion"
Sorry for any typos.
Karen Smith.
On 27 May 1998 05:14:39 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
>K Smith (drif...@nospamwebrider.net.au) wrote:
>
>> Marcus,
>
>> Yes I would agree.
>
>We agree that the I/O engine gets a workout, as originally said?
>
>This other stuff about comparing the commercial truck engines to
>commercial inboards was great. I hope we get lots more like it.
>
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> No I meant torque, you'll note I was talking about the power
> curve, being the power the engine can generate at various
> revs. against the power curve of the propeller, being the power
> consumed by the propeller at various revs. (power being an amalgam
> of torque & revs)
> Torque & revs are the [ ???] of power, so what I was saying
> was that the torque consumed by the propeller drops much quicker
> than the revs. & yes it could be expressed as the total power
> required drops, but what I was trying to accentuate was not the
> obvious that the prop requires less power to turn slower, but that
> it required alot less torque than the engine was capable of making
> at any revs lower than max. (assumming the prop is pitched correctly
> to match max. revs.)
Power = Torque x RPM.
Let's say we're running at some torque and RPM. If we close the
throttle such that power drops to 50%, then the boat will slow to 71%,
which means RPM drops to 71%, therefore torque drops to 71% too. The
torque does NOT drop much quicker than the revs, but drops about the
SAME as revs--power drops quicker than revs, not torque. That is,
unless I'm mistaken about the relationship between power, RPM and boat
speed, but I did look them up.
The full-throttle power curve doesn't enter into it, since we're not
operating at WOT anymore. Yes, at 1/2 power the boat engine is
producing a "lot less torque" than it would at the same RPM if we were
running WOT. Torque may fall off 10-20% between max torque RPM and max
HP RPM, so maybe we should adjust that 29% drop to be "30-40% below
max torque". But the torque is still pretty high, and it tracks
roughly linearly with the boat speed as long as the speed is in the
regime where speed goes as power squared, not quite as you have put
it.
> So to maintain say 3/4 revs only requires say 1/2 throttle,
> because at 3/4 revs most engines are at their max. torque range,
> provided the throttle is opened & a load applied to consume that
> load, that being the essence of my argument that the prop is
> incapable of applying a load that the engine will need any real
> throttle to overcome. (other than max. & near max.)
That does make sense, I think. The correct prop in general doesn't
load the engine to 100% torque at 75% RPM. At 75% RPM, we'd have 75%
torque, not 100%.
In a car, you could have the pedal to the floor operating in an RPM
range for max torque, 75% RPM and 100% torque. You wouldn't do this
very long if you were smart, but you could do it. You could do it in a
boat too if the prop is too tall. Proper gear selection on a car is
analogous to proper propeller selection on a boat. We might say that
when the gear is properly selected, the car is incapable of applying a
sustained load that the engine will need any real throttle to
overcome.
But we have to go uphill some time :-)
In a boat, it's "uphill" all the time.
> I liken it to a car at high speed cruise in flat country,
> maybe very high speed but that of itself is not a problem to the
> longevity of the engine. (most modern cars, for pollution, noise &
> economy reasons are incapable of max revs. in top gear on flat road)
The car uses whatever HP it needs to maintain say 80 KPH (That's 50
MPH to us yanks). The car doesn't know about power curves and RPMs--it
will consume the same power at whatever RPM the engine runs, be it
2400 in 5th gear or 3000 in 4th. This is just like a boat with
different props. Just like for a boat, the car needs to operate up to
the RPM where it generates max HP to achieve max vehicle speed, which
may mean selecting a "shorter" gear to achieve max RPM. No problem so
far.
Here's the problem: we don't run our cars in the power ranges that we
run our boats. It takes very few HP to get a car to maintain for
example 80 KPH--you barely have to open the throttle on the typical
car. About 10 HP is all it takes in the case of the Honda CRX,
according to the published figures from a few years back. I think it's
geared for about 50 MPH at 2400 RPM (I had the wagon version), which
would mean we're sucking a mere 22 ft-lb (excuse my US-centric units)
from the 1.5 liter 4-banger. That's about 1/4 to 1/3 the max torque of
that engine, 1/3 to 1/2 the max RPM, and about 1/8 to 1/6 the max
power.
Take that same engine, put it on a boat (with correct propping), and
you'll want to run it at 2/3 to 3/4 max speed. This means you will run
about 2/3 to 3/4 max RPM and torque, and about 1/2 max power,
according to the relationships between speed, power, RPM, and torque.
Going from car to boat, you tripled the power, doubled the torque, and
increased RPM by only another 1/2. This implies that the car engine
was enjoying the high RPM, low torque side of life more than the boat
engine did.
I don't think it is very different for bigger passenger car and light
truck engines typically mated to I/O's. If anything, the big honkin'
V8 is working more easily in the go-fast car than is the 4-banger in
the econobox I used by example. Because the V8 is sized for
accelleration, the vast reserve of torque and power may be called upon
for seconds at a time, but steady high-speed cruising barely scratches
the surface of the engine's capabilities. Put that same engine in a
pleasureboat, and those capabilities will be tested on a much more
severe and regular basis.
So maybe it's not as bad as Harry and I said it originally. I don't
think it's as rosy pink as you have made it out to be either, not for
an I/O engine anyway. But treat it well, and it will last a long time
nonetheless.
All bets are off for big honkin' commercial truck engines vs. their
seafaring inboard counterparts :-)
Mark75H
SNIP...
>On 27 May 1998 16:07:26 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
>~Power = Torque x RPM.
~
Marcus, are you describing standard horsepower here? If so, you have left out
the constant : 5252 belongs under the Torque x RPM and would flaw some of
your math if I am not mistaken.
Sam
Mark75H
Karen, I need you to clarify some things for me, please.
>On Wed, 27 May 1998 12:08:59 GMT, drif...@nospamwebrider.net.au (K Smith) wrote:
SNIPPED a lot o'stuff to get here...
>........... raw water cooled, which is a disaster, the consequences are;
~
>(i) The oil never gets to proper temp. & degrades/contaminates much quicker than in an
> auto, it's like a constant run at partial warmup,
~
>(ii) The oil additives are designed to reduce carbon build up in the top of the engine,
> rings & valves especially, constant mid temp (150-160f) operation allows much quicker
> deposit build up.
SNIPPED out some more here in a different part of the subject>>>>>>>
> Further the "pressure cap" subjects the cooling system to pressure, one
>reason being to increase the boiling point of the coolant, but the main reason is to
>suppress cavitation/erosion.
>(iv) So fresh or saltwater, raw water cooling is a big no no.
~
>~ The outcome of all this is that the I/Os don't last as long as they should
In the first section, are you saying RAW water cooled engines' thermostats that
control whether water goes thru the block or just out to the exhaust manifolds
are generally too cold or just don't exist?
In the second section, as I understand physics, cavitation is boiling. In order
for the cavitation induced erosion to be significantly reduced, wouldn't the
COOLING SYSTEM pressure would have to be equal to the shock wave/cavitation
pressure? 10, 15, or 20 psi isn't that much for a shockwave, rarely are spark
ignition motor's cooling systems increased much more than that.
Sam
Marcus G Bell
I was describing power and torque in an arbitrary system of units most
of the time. Horsepower is one unit of power, watts would have been
another. Yes, to get "horsepower" from RPM and foot-pounds, you need
to divide (footpounds x RPM) by 5252.
My math is not flawed by this, because I used relative numbers except
where I quoted the figures for the Honda CRX example. There, I used
2400 RPM and 10 HP to arrive at 22 ft-lb with the appropriate
conversion factor.
Power = force x distance / time, which can come from
force X radius X angular velocity, which can be rearranged as
torque X RPM.
5252 comes from 1 HP per foot-poundforce per minute per 2 Pi radians
per revolution.
Rob
Sam,
Cavitation and the boiling of water are not the same thing - although
visually they can look similar. Cavitation occurs from compression waves
present in a liquid. As Karen pointed out, these waves are generated from
the combustion cycle and are transmitted into the coolant surrounding the
cylinder wall. They are independent of the coolant temperature and/or its
pressure, however, cavitation can be effected by them. Cavitation occurs
during the rarefaction portion of the cycle when the pressure in the wave is
below ambient. These bubbles tend to form at surfaces in contact with the
liquid such as the cylinder wall. Certain forms of cavitation are very
destructive having peak values of 13,000 F and/or pressures up to 75,000 PSI
when they collapse - this is what erodes the cylinder wall. To combat this
problem, automotive manufacturers have developed anti-freeze additives that
increases its tensile strength. This helps to reduce the formation of
cavitation.
Not all engines produce cavitation and the problem occurs more with diesels
than gasoline motors (more intense combustion). I have to disagree with
Karen about cylinder flex. Nothing is perfectly rigid and the fact that
cavitation occurs indicates it is moving perpendicular to the bore. I would
suspect that engine design plays a significant role whether this will be a
problem or not. Cavitation does not occur in a standing wave and motor
designers must be aware of this - who knows, maybe it's a crapshoot.
Rob
Mark75H wrote in message <356c9292...@news.erols.com>...
K Smith
Marcus,
I meant torque & revs are the power (sorry typo)
Just for the moment, I'll forget the boat, displacement planing whatever I'll just
forget it for now.
The prop is a load (dyno) which requires a certain torque to be turned @ 1000 rpm,
another, much increased for 2000 rpm, 3000, 4000 & so on.
Engines on real dynos can be revved out to near max. with virtually no throttle
provided there is no load applied from the dyno, the engine is happy, no load just revs,
then as the load is progressively applied the throttle needs to be opened more & more to
maintain max. revs, now the motor is working hard particularly when there is no more
throttle to open & any additional load reduces revs. (scary bananas) The only thing that
has changed throughout the exercise is the torque output from the engine because the revs
have stayed the same, the "power" as a converted measurement has changed, but "power" is
just a convenient way we express work done in a certain time in this case an amalgam of
revs & torque.
Auto engines, of the type we're talking produce less "torque" at max rpm than at
about 2/3 to 3/4 max revs. (i.e. with the throttle fully open) The power curve is merely a
plot of the engines torque output at full throttle, at various revs.
Now the propeller has a power consumption curve in the same manner,(I've seen the
magazine type articles that express the "power" delivered/consumed at various prop/boat
speeds but that isn't relevant here) the revs vs torque required.
In my original post I pointed to the stark contrast between the two curves,
reading the same info (revs & torque) & said that the engine is loafing at 3/4 revs
because the torque requirement has virtually gone away. (I didn't mention the gearbox
reduction because it's not relevant)
So your Honda, (auto or manual) how many times did you find yourself cruising in
give & take country, go to pass or accelerate, only to find there was no more left &
unknown to you your foot had been very close to the floor probably for some time. This
happens all the time, every time you take off, if the engine doesn't freely react to your
foot opening the throttle (like it does in a boat) then it is loaded & working, even more
in manuals with people who think they are caring for their engine by not revving it.
Even in the suburbs auto engines work, repeatedly accelerating, climbing hills &
having the load constantly go from too much to none. The accepted conversion for road
engines is 80000 clicks = 1000hrs, needless to say people don't swan around averaging 80
kph (50mph) but that is how the engines "look" after examination. In other words the
coasting down hill, idling, etc. doesn't count, nor should it but pulling 1200-1300 kg
from rest to 50mph in under 15 secs. say 20 times, climbing hills, accelerating to join
traffic etc. etc. going to work from dead cold, then repeating it of an evening, again
from dead cold, is definitely "counted".
Karen Smith.
On 27 May 1998 16:07:26 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
Marcus G Bell
So I was thinking "hmmm, once before I was talking about engines used
on I/O's, but she was talking about commercial inboards, I wonder if
it's happening again? Maybe she's talking about displacement hulls
rather than the planing hulls I'm talking about." And then, reading
through the thread again, I got to the part where you say:
> Your comments about power required to plane, then the greatly
> reduced amount of power required to cruise once on the plane are I
> guess true, but not relevant to what I was saying, which remains
> true of a heavy displacement vessel as a planing type.
OK, yes, what you said is for displacement speeds, what I've been
talking about are planing speeds.
The power/speed curve of displacement hulls is different from that of
planing hulls, in that speed goes as power (think think) cubed, right?
This makes torque exponential with RPM, as you said. Everything else
you said follows from that.
Part of my confusion may have been that the original question and
initial responses were about I/O's which are generally fitted to
planing craft. Am I correct that your responses have been more
relevant to non-planing craft? That would clear up a lot of where we
seemed to be at odds.
Maybe we can agree to agree :-)
To recap--
Outboards are designed from the beginning for the application for
which they are used.
I/O engines are mostly made from major parts developed for automotive
or light truck engines, with certain marine-specific modifications.
These engines are generally fitted to planing hulls and work harder
than their land-locked counterparts.
However, in practice engines fitted to non-planing hulls often have an
easy life compared to the heavy truck or industrial engines upon which
many larger inboards are based.
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> Marcus,
> I meant torque & revs are the power (sorry typo)
It seems we've both been busily pecking away and having our notes
cross in the wire, so to speak.
> The prop is a load (dyno) which requires a certain torque to
> be turned @ 1000 rpm, another, much increased for 2000 rpm, 3000,
> 4000 & so on. [snip]
OK. We're on the same track.
> Auto engines, of the type we're talking produce less "torque"
> at max rpm than at about 2/3 to 3/4 max revs. (i.e. with the
> throttle fully open) The power curve is merely a plot of the engines
> torque output at full throttle, at various revs.
It is my understanding that marine engine torque peaks at higher RPM
than that of the auto engine, with changes in valve timing, induction,
etc. Let's confine this particular bit of discussion to real marine
engines perhaps based on an automotive block, not just an auto motor
"conversion" with marine flame arrestor, alternator, starter, etc. Am
I correct, way off, so-so?
> Now the propeller has a power consumption curve in the same
> manner,(I've seen the magazine type articles that express the
> "power" delivered/consumed at various prop/boat speeds but that
> isn't relevant here) the revs vs torque required. In my original
> post I pointed to the stark contrast between the two curves, reading
> the same info (revs & torque) & said that the engine is loafing at
> 3/4 revs because the torque requirement has virtually gone away. (I
> didn't mention the gearbox reduction because it's not relevant)
Yes, I can see how the torque/RPM curve of the prop could
significantly undercut the WOT torque/RPM curve of the engine.
But the power/speed curve of the boat is 100% relevant. The system is
not a prop static in the water, but a coupling of speed, drag forces
on the hull, prop thrust and torque and RPM.
It really does depend on the power/speed relationship of the boat.
Case in point: a very efficient planing hull will have speed
proportional to power. Let's hang on it a motor that has max torque
flat between 2/3 and max RPM, not unrealistic for high-revving
engines. Now, let's throttle back to 2/3 RPM and 2/3 speed, which for
this hull will mean 2/3 power. But wait, 2/3 power at 2/3 RPM means
that torque is still riding at MAX.
Didn't like that because of the flat torque curve? OK, let's go for a
20% drop between 2/3 and max RPM. 2/3 RPM, 2/3 speed, 2/3 power, but
80% torque this time. The only time this engine sees 100% torque is
during acceleration before the boat gets up to speed and unloads the
prop.
Now, for a boat whose speed goes as power to the 1/3 or less, like a
displacement hull, torque falls off faster than RPM, and what you say
about the engine "loafing at 3/4 revs because the torque requirement
has virtually gone away" becomes much closer to the reality.
> So your Honda, (auto or manual) how many times did you find
> yourself cruising in give & take country, go to pass or accelerate,
> only to find there was no more left & unknown to you your foot had
> been very close to the floor probably for some time. This happens
> all the time, every time you take off, if the engine doesn't freely
> react to your foot opening the throttle (like it does in a boat)
> then it is loaded & working, even more in manuals with people who
> think they are caring for their engine by not revving it.
Truth? Once. Car fully loaded, going 35 MPH in snow, so I had it in
5th (stickshift) to keep the torque deliberately low to the
drivewheels (front). Started going uphill, spent about 5 seconds at
2/3 throttle, bumping up to WOT failed to provide any increase in
pressure to my back pressed against the seat, downshifted to 4th to
maintain 35 at 1/3 throttle. Would have gone for 3rd, but didn't want
to pop the wheels loose in the snow with the increase in torque upon
declutching. If I had an automatic tranny, it would have downshifted
as soon as manifold vacuum dropped or I exceeded 3/4 throttle and
activated the kickdown, and it would have sent me spinning.
Lugging the engine at high throttle and low RPM is punishable by death
(to the engine) and thus it just isn't done. Even when towing at
highway speed, if I exceed 1/2 throttle at 68 MPH in 5th for more than
a few seconds, it's because the hill is too steep for my underpowered
rig and I need to downshift to 4th. So I do, and that takes me back to
62 MPH because I can't stand the rattle of the engine revving that
high.
Heavy accelleration is performed between 3300 and 4400 RPM, though
merely maintaining drops it back to about 2200 to 2600 and low
throttle.
Oh, it just occurs to me that rate of valve wear increases at high
RPM, regardless of what the rest of the engine is doing.
I'm undermining your example, and I realize you're trying to paint a
general picture about how most drivers abuse their engines. So let's
not focus on me, let's look at most other drivers in my country.
Most other drivers have an automatic tranny and have nothing to do
with selecting the RPM or torque of the engine. Between the gearbox
and engine is a torque convertor that allows the engine to spin up to
higher revs quickly, meantime multiplying the engine torque. The
driver calls for more power, the engine delivers it, end of story. If
the call for power exceeds some level (often determined using manifold
vacuum and throttle position) the transmission may downshift to allow
more engine RPM, hence more HP from the engine makes it to the
drivewheels at a higher torque through the gear reduction. If the
torque convertor has a "lockout" which eliminates "slip" for better
economy, the lockout will have disengaged well before the downshift.
In other words, most other drivers are already driving boats, as far
as the engine is concerned. The difference is that their cars cruise
at 10 to 20% power much of the time, and maybe 20-30% torque. And of
these drivers, it is the rare driver indeed who would need to run at
2/3 throttle, generating upwards of 2/3 torque, for more than a few
seconds' stretch. This same driver will hop in a boat and think
nothing of doing just that for hours at a time, in an I/O-powered
planing pleasurecraft.
> Even in the suburbs auto engines work, repeatedly
> accelerating, climbing hills & having the load constantly go from
> too much to none ... accelerating to join traffic etc. etc. going to
> work from dead cold, then repeating it of an evening, again from
> dead cold, is definitely "counted".
True.
Except for the part about "too much load" which is specific to a stick
shift as I understand your meaning of "load". The automatic keeps the
engine running at high RPM during heavy accelleration, and as such,
"load" is kept more tolerable.
I have been enjoying this immensly and have been learning a lot. I
hope the same for you and for those who are tuned in.
Marcus G Bell
Rob (r...@deltanet.com) wrote:
> Cavitation and the boiling of water are not the same thing -
> although visually they can look similar. Cavitation occurs from
> compression waves present in a liquid. [snip]
Cavitation is a void in the water brought about by a local low
pressure area. The water surrounding the void may boil at ambient
temperature in the low pressure interface.
To someone who works with propellers a lot, cavitation occurs in the
vacuum behind the rotating propeller. (It is NOT when air gets sucked
into the prop--that's ventillation.) I guess you might be able to call
this vacuum a "compression wave" (expansion wave?), but that may be
stretching it (pun not intended).
Perhaps this form of cavitation in the water jacket and behind the
propeller are not strictly speaking the same thing, but the effects
you describe of the collapse of the void destroying material it
contacts are very similar. I have a cavitation-damaged prop out in the
garage, as do many like me.
There has been previously mentioned cavitation due to bulk flow of
coolant in the tortuous water passageways, with attendant local low
pressure zones. You can simulate this with a kinked garden hose and
hear the "boiling". This is more analogous to the prop cavitation and
would be affected by coolant pressure.
The cavitation generated by the acoustic waves through the cylinder
bores is fascinating stuff. The way you describe it makes a lot of
sense.
K Smith
Sam,
Yes the marine engines have thermostats, but they usually open at about 140 deg.F
as opposed to at least 180, but these days alot of auto engines have 195 F thermostats.
Seawater particularly, can't be run at 195 F as the salts start to drop out & deposit. The
lower temp. thermostat is also used as defacto oil cooling.
The exact physics of "cavitation" are much & often discussed, seemingly without
final resolution. Whatever, the higher the static pressure the less cavitation, pressure
doesn't eliminate, it just minimises when coupled with the correct inhibitors (which raw
water cooled I/O don't have) a good service life can be obtained.
Oops, sorry Sam I wrote this before I saw Rob's comments on the subject, I defer.
Karen Smith.
On Wed, 27 May 1998 22:55:33 GMT, Mar...@AOL.com (Mark75H) wrote:
>Karen, I need you to clarify some things for me, please.
>
>>On Wed, 27 May 1998 12:08:59 GMT, drif...@nospamwebrider.net.au (K Smith) wrote:
>
> SNIPPED a lot o'stuff to get here...
>
>>........... raw water cooled, which is a disaster, the consequences are;
>~
>>(i) The oil never gets to proper temp. & degrades/contaminates much quicker than in an
>> auto, it's like a constant run at partial warmup,
>~
>>(ii) The oil additives are designed to reduce carbon build up in the top of the engine,
>> rings & valves especially, constant mid temp (150-160f) operation allows much quicker
>> deposit build up.
>SNIPPED out some more here in a different part of the subject>>>>>>>
>> Further the "pressure cap" subjects the cooling system to pressure, one
>>reason being to increase the boiling point of the coolant, but the main reason is to
>>suppress cavitation/erosion.
>>(iv) So fresh or saltwater, raw water cooling is a big no no.
>~
>>~ The outcome of all this is that the I/Os don't last as long as they should
>
>
>In the first section, are you saying RAW water cooled engines' thermostats that
>control whether water goes thru the block or just out to the exhaust manifolds
>are generally too cold or just don't exist?
>
K Smith
Marcus,
I guess I'm going on about this sorry, but it has occurred to me that a succinct
way of summing me up is;
Most boats, regardless of hull type, performance, diesel, petrol, inboard, I/O or
O/B, spend most of their operating hours between 2/3 & 3/4 of max. revs. To maintain these
revs a fixed pitch propeller usually only requires about 1/2 throttle.
A marine engine operated at mostly 1/2 throttle, with correct oil, coolant temps &
maintenance should potentially last a long time.
I know it's off subject but, auto transmissions are designed to get the best
performance or economy as set, but they extract, (particularly when set to economy) alot
of load/torque from the engine. This is readily seen in a manifold vacuum gauge. Autos
usually won't "kick down" above a modest speed (110ks or 65mph) & there is no trouble
"lugging" an engine, particularly rec. boaters towing.
Karen Smith.
K Smith
Marcus,
Ahh... umm... er..., sorry it's me again. (you're not trying to bait me are you? I
thought you guys had finished with "how to kill a cat")
I agree O/Bs are designed from the beginning for the purpose but I don't think it
follows that the I/O is inferior, nor have I conceded as a tech. fact, in planing or any
other hull that they work harder than their land locked cousins, but of course I respect
your opinion.
As I said yesterday, I think O/B suffer most of the shortcomings of I/O so I'll
stick with my original, It's a matter of opinion.
They both use an aluminium lower unit which has incredibly poor reliabilty, such
that whatever the outcome of who's engine is most reliable, the leg/drive mostly fails
long before either die.
Karen Smith.
Marcus G Bell
The following paragraph contains a poorly worded phrase. I believe
the context was fairly clear, but in the interest of reducing
confusion, and I'd like to amend it nonetheless. Thank you.
Marcus G Bell (be...@mail.med.upenn.edu) wrote:
> In other words, most other drivers are already driving boats, as far
> as the engine is concerned. The difference is that their cars cruise
> at 10 to 20% power much of the time, and maybe 20-30% torque. And of
> these drivers, it is the rare driver indeed who would need to run at
> 2/3 throttle, generating upwards of 2/3 torque, for more than a few
> seconds' stretch. This same driver will hop in a boat and think
> nothing of doing just that for hours at a time, in an I/O-powered
> planing pleasurecraft.
*** amended paragraph follows ***
In other words, most other drivers are already driving boats, as far
as the engine is concerned. The difference is that their cars cruise
at 10 to 20% power much of the time, and maybe 20-30% torque. And of
these drivers, it is the rare driver indeed who would need to run at
2/3 throttle, generating upwards of 2/3 torque, for more than a few
seconds' stretch. ***But most drivers would*** hop in a boat and think
nothing of doing just that for hours at a time, in an I/O-powered
planing pleasurecraft.
--
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> Marcus,
> Ahh... umm... er..., sorry it's me again. (you're not trying
> to bait me are you? I thought you guys had finished with "how to
> kill a cat")
Just trying to get at the bottom of an interesting issue :-)
> I agree O/Bs are designed from the beginning for the purpose
> but I don't think it follows that the I/O is inferior, nor have I
> conceded as a tech. fact, in planing or any other hull that they
> work harder than their land locked cousins, but of course I respect
> your opinion.
I think our differences in opinion may come as a result of our
somewhat different predjudices about how cars and boats are most often
operated. That's OK. My horizons have been expanded now.
> As I said yesterday, I think O/B suffer most of the
> shortcomings of I/O so I'll stick with my original, It's a matter of
> opinion.
> They both use an aluminium lower unit which has incredibly
> poor reliabilty, such that whatever the outcome of who's engine is
> most reliable, the leg/drive mostly fails long before either die.
I think the I/O is the worst part of an outboard coupled to the worst
part of an inboard. That said, I agree that it doesn't make them
inferior to an outboard. Just different. Vive la difference! The
choice of outboard over/under I/O depends on the type of craft,
intended use, and lots of other things.
As almost everyone agrees, maintenance will make any propulsion last a
long time, provided the operating parameters are kept within some
margin of safety.
hidda
K Smith wrote:
>
> Marcus,
>
> Ahh... umm... er..., sorry it's me again. (you're not trying to bait me are you? I
> thought you guys had finished with "how to kill a cat")
>
> follows that the I/O is inferior, nor have I conceded as a tech. fact, in planing or any
> other hull that they work harder than their land locked cousins, but of course I respect
> your opinion.
>
> stick with my original, It's a matter of opinion.
>
> They both use an aluminium lower unit which has incredibly poor reliabilty, such
> that whatever the outcome of who's engine is most reliable, the leg/drive mostly fails
> long before either die.
>
>
<Snipped>
Well, not in all cases. I know of dozens of 20 year old Volvo outdrives
that have outlasted at least one repower. I have a 290 DPA drive that's
got 2,000 hours on it and has only required normal maintenance and shows
no signs of wear such as water or unusual amounts of metal in the oil.
Although there are a lot of dings, the bare metal shows no signs of any
corrosion damage. If I keep this boat much longer, I'm sure I'll need
to repower, but the leg will still go on.
As to the question of which engine works harder, one on a boat or in a
car, I have a question. How much horsepower is required to keep a car
running at 30 mph on a level road with a normal load and how much
horsepower is required to keep a boat that weighs the same as the car
running at 30 mph on the water?
I have another question. What about comparing a tug boat that's heading
up the river at hull speed, versus the same tug boat heading up the same
river at the same hull speed with a fully loaded tow? How does this
scenario fit in with what you've been talking about?
One final question. Why is lugging a boat engine not harmful? Take the
case of a boat with a planing hull. You operate it at just below
planing speed. Stern dug in. Bow up in the air. To go from point A to
point B, you're burning up a huge amount of fuel. Make the same run at
planing speed. You'll burn a lot less fuel. Make the run at a slow
displacement speed and you'll burn even less (assuming zero current and
wind in all examples). You're telling me that going a given distance
while burning the max amount of fuel is not harmful to an engine when
compared to running the boat at a more economical mode? Can you explain
this to the non-engineers in layman's terms?
Dennis
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> Marcus,
> I guess I'm going on about this sorry, but it has occurred to
> me that a succinct way of summing me up is;
> Most boats, regardless of hull type, performance, diesel,
> petrol, inboard, I/O or O/B, spend most of their operating hours
> between 2/3 & 3/4 of max. revs. To maintain these revs a fixed pitch
> propeller usually only requires about 1/2 throttle.
> A marine engine operated at mostly 1/2 throttle, with correct
> oil, coolant temps & maintenance should potentially last a long
> time.
Yup yup. I think that's all fine and good.
But most automobiles and light trucks here (US) are "overpowered" by
other standards and will seldom see sustained 1/2 throttle, especially
when coupled to an automatic transmission. But versions of these
engines *will* see these conditions regularly on a boat. That's where
I'm coming from.
This by itself doesn't necessarily mean the I/O engine will blow up
faster than an outboard, as probably I implied earlier. So I amend my
previous remark on that. It's just food for thought, I guess.
> I know it's off subject but, auto transmissions are designed
> to get the best performance or economy as set, but they extract,
> (particularly when set to economy) alot of load/torque from the
> engine. This is readily seen in a manifold vacuum gauge. Autos
> usually won't "kick down" above a modest speed (110ks or 65mph) &
> there is no trouble "lugging" an engine, particularly rec. boaters
> towing.
The population of folks towing with their overpowered cars and light
trucks is small, and the engines are probably designed for only
intermittent high load and priced accordingly. Most auto trannys do
not have selectable performance and economy modes, and are geared and
programmed for a tradeoff of economy and performance, since the public
hates to tromp the pedal and feel no accelleration. You can achieve
this by gearing it tall, but allowing it to downshift freely by
sensing engine load. The majority of auto-tranny cars I've had the
misfortune to drive will kick down with sustained load even above 65
MPH, often because the throttle position triggers a kickdown actuator.
Where there is a torque convertor lockout, a modest increase in engine
load will often disable the lockout and allow RPM to "float" upwards
till the load decreases again. The downshifting especially will lead
to "hunting" since the unloaded hiher-revving engine will now require
less throttle, which increases manifold vacuum, which lets the tranny
upshift again which increases load, and the cycle repeats. "Smart"
controllers are reducing this, but it's still a ways from the general
case. The bigger engines upon which many I/O powerplants are based
were developed years ago for the old style slushbox.
Rob
Let's try this definition:
"Cavitation" refers to the formation and the subsequent dynamic life of
bubbles in liquid. These bubbles can be either gas or vapor filled and form
in a wide variety of liquids under a wide range of conditions. It may be
hydrodynamic, thermal, or acoustic in origin and occurs where the tensile
strength of the liquid is exceeded. It is unlikely that the true tensile
strength of the liquid is ever reached because most liquids contain nuclei
about which cavitation bubbles originate - dispersed dust particles,
prominences on immersed surfaces, or minute gas bubbles.
There may be two of these forms at work here; hydrodynamic due to "bulk
flow of coolant in the tortuous water passageways", and acoustical due to
the combustion event. I suspect the latter is responsible for the pin-holes
that develop in certain motors. Karen pointed out that these pin-holes tend
to form 90 deg from the wrist pin which makes sense. This area of the
cylinder wall is less supported and thereby more likely to resonant
increasing the possibility of cavitation at this point. Of course any form
of cavitation lowers the ability of the coolant to transport heat - not
good.
Do you think the outboard designers pay attention to this stuff, or have
they just been lucky?
Rob
Marcus G Bell wrote in message <6kiog1$8nh$1...@netnews.upenn.edu>...
Rob
Why don't you look at it in terms of fuel consumption. My boat gets about 3
MPG cruising while my van gets about 15 on the highway (except when I am
towing the boat, then maybe 10). Lets see, my outboard is rated 200 HP and
my van about 180 HP - that's close enough. Who's working more? I think my
boat motor is always working more and it will never do better than 3 MPG.
You could look at it as GPH - same thing. I can't tell anymore but is that
what this discussion is about?
Rob
Mark75H
>On 27 May 1998 23:31:17 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
>~I was describing power and torque in an arbitrary system of units
Thanks for the clarification, it did look like you were using arbitrary units
to me, but I wanted everyone to know this, and that it did change the math
somewhat from other descriptions. "Arbitrary" is a super word here, from the
same root that Germans still use for their word for "work". Sometimes the
simpler "working" units are easier to use in brief examples.
Sam
Big Smoke
Depends on which O/B you're talking about. I can site one particular case that
backs that up. My friend and his cousin both bought boats ~10 ears ago. One a
110 hp Evinrude, the other a 135 hp Merc. Both were set up properly, propped
accordingly etc. Both were maintained well. The Merc has no where near the
hours the Evinrude has and now, ten years later, the Merc's spitting pistons.
The OMC looks very clean inside and, with the exception of the usual wear and
tear, is in exceptional condition considering the mileage. He's the first in
and last out every season and boats virtually every weekend in the summer. Once
at the cottage for the weekend the boat is the major mode of transportation for
him. The Merc is used far less frequently.
Don't get me wrong, Merc makes a good product. The people I've talked to
indicate that the problem with Mercs performance motors is life span. Getting
more from less costs in the long run. Squeeze 260 hp out of a 2.5 litre motor
running a 7500 rpm and it's not gonna last as long as a 3 litre kicking out 250
hp at 6000 rpm, no matter what the care taken in maintainence. Approx 5% more hp
with 20% less displacement turning 25% faster, you're gonna have problems
sooner. The fact alone that the 80's 135 hp Merc is a detuned 200 block should
account for increased life as the motor is not working to produce its full
potential. The V4 on the other hand is running at full power since the most
that comes out of that block is 110hp.
IMHO, the bottom line is, if you want performance go with Merc, if you want life
span go with OMC.
As far as the question between I/O vs. O/B, my preference goes with O/B for
sure. Compare the power to weight ratios on equal hp I/Os vs. O/Bs. Both at
300 hp the Merc ProMax 300 O/B weighs in at 467 lbs vs. the Merc 350 Magnum MPI
Gen+ I/O at over 1000 lbs. What you are looking for depends on what the
application. I'm quite sure that 4-stroke I/Os make torque at lower rpms making
it better siuted to heavier loads. If your boat is under the 20' mark then a
O/B is definately the way to go (IMHO). Some say that they are equally easy to
maintain. I prefer to be outside my boat staning on the ground when wrenching
my motor than in a cramped engine compartment. The upgrade possibilities are
easier with an O/B also.
I'm not a mechanic or salesman, just an average joe, so don't jump on me guys if
I got something wrong. Just going with mine and other boaters experiences. I
could be dead wrong and would gladly accept any CONSTRUCTIVE critique of what
I've said.
Happy Boating,
Big Smoke.
Marcus G Bell
> >On 27 May 1998 23:31:17 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
> >~I was describing power and torque in an arbitrary system of units
Mark75H (Mar...@AOL.com) wrote:
> Thanks for the clarification, it did look like you were using
> arbitrary units to me, but I wanted everyone to know this, and that
> it did change the math somewhat from other descriptions.
I dunno, 50% torque is 50% torque regardless of units, which is as far
as I ever took the math except for a single calculation.
If what you mean is
"power = torque X rpm" does not imply "HP = ft-lb X rpm"
then yes, we need to make that distinction. In the first relation,
units of power and torque are never specified, and in the second, the
magic 5252 conversion factor is missing.
> "Arbitrary" is a super word here, from the same root that Germans
> still use for their word for "work". Sometimes the simpler
> "working" units are easier to use in brief examples.
Yes, when you're talking relative numbers, units can be left
arbitrary. Then it may become time to relate it to something real,
like "10 HP and 22 ft-lb to go 50 MPH at 2400 RPM."
hidda
K Smith wrote:
>
> Dennis,
>
> I definitely wasn't casting aspersions on your Volvo leg, apologies if you took
> offence, it was a generalised comment on the state of the technology, rather than any
> particular units/brands.
>
> I'm not sure about how much HP is required to maintain a car @ 30mph, there are
> heaps of variables, but a good conceptual thing I use is that a new slippery shape US
> compact (Ford, GM) requires about 30 hp continuous to maintain 100 kph (65mph) on flat
> road, no wind etc. etc. whereas a pantec (not the big ones the mid size, we call them 8-12
> tonners) requires over 100hp in the same situation.
>
> Equally I don't know how much HP is required to hold your boat on the plane at a
> particular speed, the "variables" go through the roof.
>
> You can work it out yourself. (N.B.there is absolutely no accuracy here, very
> rough but it is a good indicator) You'll need a vacuum gauge or absolute manifold
> pressure gauge, (probably one of those K mart tune up vacuum types will do.) Temporarily
> install to a vacuum source (there are lots of spare unused inlet manifold plugs on marine
> conversions, go for one closest to the carb.) take the boat to the desired revs, & open
> the throttle fully & quickly note the lowest vacuum reading, then note the reading again
> when you are back at the same cruise setting (say 1/2 throttle, 2/3 to 3/4 revs) Get a
> power graph for your engine, usually somewhere in the owners manual, but if not don't use
> say a GM one for their auto engines it will be different. With the power curve graph,
> check the max HP available at your cruise revs, I'm only guessing but say 120-140 hp then
> reduce that by the amount the vacuum reading increased from the max throttle reading, as a
> percentage of say 30 inches. (Say at full throttle it read NIL, it won't but, then at
> cruise it read 15 in. that would be about a 50% power reduction or 60-70hp, if you or a
> friend fly light planes they'll know exactly what to do, although they usually work on
> absolute manifold pressure)
>
> The unrestrained tug boat, at hull speed is usually not at full throttle & the
> same comments apply, but when it is towing the throttle is usually open further, maybe at
> times fully open & yes the engine is loaded, but not when the throttle is at say 1/2.
>
> Lugging a boat engine is possible in the circumstances you describe & yeah I guess
> it's just as harmful as any other type of "lugging", in the context I just assumed most
> rec. boaters don't spend too much time as a percentage of the total in that situation.
>
> Karen Smith.
>
<Snipped>
Karen,
I just wanted to point out that you can make generalizations, but there
are exceptions and I pointed out a few. I guess I still don't buy some
of what you're saying, hence the cited exceptions.
I'll be the first to admit that I'm not an engineer and I barely passed
calc in college. On the other hand, I do have a lot of questions and I
like to find the answers.
I used the example of a car going 30 mph and a boat going 30 mph because
both speeds are easily attainable. I'd guess that a large number of
boats spend a significant amount of time below 30 mph. I'd bet a car
going 30 uses 10 hp or less. The same weight boat on the other hand
would use more than 10 hp. How do I know that? Because I've been on
4,000 lb boats with 15 hp. kickers that could barely maintain 10 knots!
Anyway, I still believe anything that's operating under a big load will
have a shorter life than the same thing loafing along at 1/2 load. I
could see where in a frictionless environment, it would take the same
amount of energy to keep an object going at a certain speed as it would
to keep an object infinitely bigger going at the same speed. On the
other hand, to accelerate to that speed is another story.
In the real world, a car on flat land mostly has wind and road friction
to deal with. Doesn't take much energy to keep it rolling at 30 mph.
However, in a boat, I still think the engine is working a lot harder
than a car's engine is. The boat is actually pushing it's weight in
water out of the way. That alone has to account for a bigger load on
the engine.
I think what you're trying to say is if you match the car's rpm with the
boat's, both will be under similar loads. So, if a car goes 60 mph at
2,000 rpm, I can tell you the same weight boat with the same engine at
2,000 rpm will not be going anywhere close to even 30 mph. From one
minute to the next, both engines could be receiving the same amount of
wear and tear. However, the boat will take more than twice the amount
of time and way more fuel to go the same distance. So, now the question
is, which engine will wear out first? After all, in the real world, we
don't really care about time as much as we care about getting from one
point to another. Put another way, distance for distance, same engine,
same weight of car and boat, the boat will use a hell of a lot more
energy to go the same distance either at the same rpms or the same
speed.
Actually, I give up. My head is sore. Why don't we talk about the
stock market instead? Or talk about what kind of lures I'm going to run
this weekend?
Like I said, I have a lot of questions.
Dennis
Marcus G Bell
> On 28 May 1998 14:55:33 GMT, be...@mail.med.upenn.edu (Marcus G Bell)
> wrote:
> >In other words, most other drivers are already driving boats, as far
> >as the engine is concerned. The difference is that their cars cruise
> >at 10 to 20% power much of the time, and maybe 20-30% torque. And of
> >these drivers, it is the rare driver indeed who would need to run at
> >2/3 throttle, generating upwards of 2/3 torque, for more than a few
> >seconds' stretch. ***But most drivers would*** hop in a boat and think
> >nothing of doing just that for hours at a time, in an I/O-powered
> >planing pleasurecraft.
Big Jim (jul...@compuserve.com) wrote:
> I guess you've never driven a 4 cylnder Jeep in Colorado, have you?
No, I haven't, and probably neither have "most drivers", which is the
market for which "most auto engines" are designed and built.
vacuo
On Thu, 28 May 1998 16:51:12, Big Smoke <air...@sprynet.com> wrote:
> Both were maintained well. The Merc has no where near the
> hours the Evinrude has and now, ten years later, the Merc's spitting pistons.
> The OMC looks very clean inside and, with the exception of the usual wear and
> tear, is in exceptional condition considering the mileage. He's the first in
> and last out every season and boats virtually every weekend in the summer. Once
> at the cottage for the weekend the boat is the major mode of transportation for
> him. The Merc is used far less frequently.
Regularity of use is a plus, as is the consistency of other variables
such as
maintenance and a more-practiced performance profile. In short, the
more
used boat is a happier boat and will wear less/ last longer.
To verify, you should find another pair of boaters with the regular
user running
a Merc and the sporadic having the OMC. Or better yet, have the
original two
switch boats for the duration (until the OMC becomes as crapped out as
the Merc).
In real life its hard to avoid the apples/oranges comparisons.
Regards,
Vacuo
-. ..--- -.- --.- .-
Marcus G Bell
Rob (r...@deltanet.com) wrote:
Yes, the discussion was along those lines.
The problem with using MPG to equate to "how hard" an engine works is
there are all kinds of things that can reduce MPG but don't
necessarily "load" the engine any more. You could be idling along and
only get 3 MPG for instance. GPH is probably the more relevant
descriptor of engine load than is MPG.
I believe one of Karen's main points has been that the boat engine
does not see the combination of low RPM and high torque that is
possible with an auto engine coupled through a transmission set up to
achieve that combination. High torque and low RPM stresses the engine
in many ways.
An interesting exercise is to compare the HP and torque figures that
accompany typical use for your boat and van.
Based on the 15 MPG at perhaps 60 MPH, you are burning 4 GPH in your
van. This works out to around 40 HP. At 2100 RPM, that's 100 ft-lbs of
torque. It would be good if we knew what speed and RPM you usually run
at, so we could clean up the math, and also how the torque figures
relate to the max torque of your engine.
Now, you will most likely run your outboard at around 2/3 revs and
half power: 100 HP, 3750 RPM. This works out to 140 ft-lbs torque. Max
torque for such a beast is in the neighborhood of 220 ft-lbs.
Using similar math, my wife's Escort wagon fully loaded needs on
average 22.5 HP, 41 ft-lb, to do 72 average MPH at 2880 RPM and 32
MPG. When we tow the boat as well, it drops to 28 MPG, with
adjustments to the other numbers. We dip into the "upper half" of the
1.9L 4-banger's 88 HP only seconds at a time, preferring to downshift
rather than stand on the throttle for extended uphill runs. I don't
have the torque figure for this engine handy, but it probably does
around 100 ft-lb peak at around 2600 RPM. The 16-valve 1.8L GT version
is more torquey at higher revs.
K Smith
Marcus,
I agree, so using my admittedly very rough numbers, say your Honda at
steady 100kph (65mph) gets over 40 mpg or uses 6.16 lpHOUR X 3 = 18 HP.
The standard full size, slippery US Ford or Gm I spoke of earlier on a
highway at 100 etc. gets about 22-25 mpg or say 10 lph X 3 = 30HP (this number
is accepted in the auto industry as right)
Rob's van I'm guessing a standard "van" has much more resistance, so his
15mpg at 100kph etc is 15.16 lph X 3 = 45 HP (Rob's analogy with his O/B isn't
fair because the discussion is about auto 4 strokes used in I/Os)
So an I/O running at a steady throttle setting, with a
constant/unchanging load regularly uses 6-7 gpHour at cruise, so 23- 27 lph =
69-81 HP, a doddle for the average US based I/O (Ford, Chevy small or big block)
They are designed to rev & have stirling angles which almost demand it.
I don't expect anyone will change their view & as I have said I think it
is really just personal opinion, but I don't think the I/O situation overloads
an auto based motor, such that it's potential longevity is compromised from the
power output demanded.
As an aside the O/Bs get the same rest at cruise.
Karen Smith.
Marcus G Bell
K Smith (drif...@nospamwebrider.net.au) wrote:
> I don't expect anyone will change their view & as I have said
> I think it is really just personal opinion, but I don't think the
> I/O situation overloads an auto based motor, such that it's
> potential longevity is compromised from the power output demanded.
I agree with this.
Actually, I have modified my view a bit over the course of this. I
still think that on average, the I/O engine works harder than the car
engine of similar size, but the work is different and the engine can
take it. Sort of a sprinter vs. distance runner kind of thing--the car
sprints then walks, sprints then walks, but the boat motor plugs away
at intermediate output. A well maintained auto or I/O engine will give
many years of great service. Same for the outboard.
MMB...@my-dejanews.com
Karen My name is Dan and I have read some of your replys regarding marine
volvo engines and thought I would ask your opinion about a boat I am
considering buying.
The boat is a 1970 model Sea Ray with a 1988 re-power using a Volvo AQ125P
4-cylinder engine. My friend who is a marine mechanic says parts are hard to
come by. Do you have any Idea if this is true?? Also he has seen these models
experience overheating problems which have resulted in warped heads and other
nasty things. FYI the outdrive is a model 270 Volvo and seems in good shape.
I feel the boat has been well maintained which could account for the fact the
motor and boat seem in good shape. I guess I am looking for any hidden design
gremlins lurking around waiting to pop out as soon as I lay down the cash!!!
Thanks for any help you can provide. Dan
>
> Marcus,
>
> Well yes & no. Yes; a converted car engine hooked onto a fixed pitch propeller
> does "get a workout" but no; not so it is bad for it or will effect it's reliability as
> per Harry's original post.
>
> As I've said, revs. don't bother an engine so long as it is within the OEM limit.
> It's load that kills.
>
> The "problem" as I see it in car engines being used in boats (mercruiser, volvo
> etc,) is the so called conversion, not the power required of the motor.
>
> Most are raw water cooled, which is a disaster, the consequences are;
>
> (i) The oil never gets to proper temp. & degrades/contaminates much quicker than in an
> auto, it's like a constant run at partial warmup,
>
> (ii) The oil additives are designed to reduce carbon build up in the top of the engine,
> rings & valves especially, constant mid temp (150-160f) operation allows much quicker
> deposit build up. (I guess you can see why I have a thing about your pal Ralph)
>
> (iii) Modern engines like Chev. use very light ring pressures (that's one of the reasons
> they last much better these days) & rely heavily on combustion pressure behind the rings
> to seal, obviously any premature carbon build up in the ring lands stops their proper
> operation/sealing & then the blowby compounds the problem quickly.
>
> (iii) The engines corrode, but this is not "rust" in the conventional sense (whilst hot
> salt water is extremely corrosive) it is cavitation, the combustion, (explosions if you
> like) set up shock waves through the bore (some say the bore actually flexes, I don't but
> some do) the shock waves go into the coolant which sees a high frequency alternating high
> & low pressure. Just like a cavitating prop the imploding bubbles so created actually
> erode the metal of the bore, block, head whatever, that is why raw water cooled engines
> usually suffer pin hole corrosion (usually at 90 deg. to wrist pin, why there?) much more
> than the same coolant cooled auto engine. The "inhibitors" in modern auto engines, coat
> the water jacket with a protective coating, which also succumbs to erosion by the
> cavitation but so long as it is changed regularly it will self repair & protect the
> underlying metal. Further the "pressure cap" subjects the cooling system to pressure, one
> reason being to increase the boiling point of the coolant, but the main reason is to
> suppress cavitation/erosion.
>
> (iv) So fresh or saltwater, raw water cooling is a big no no.
>
> The outcome of all this is that the I/Os don't last as long as they should,
> usually the bore/pistons give up, not through "wear" because they're worked hard, (because
> I say they aren't) but because of the oil degading & not keeping the pistons/rings clean,
> to a lesser extent the same happens to the valves, sludge builds up because the oil
> dispersants can't keep the contaminants in suspension etc. etc.
>
> Now if all car engines were properly converted, with heat exchangers & in most
> cases proper oil coolers, most of these problems would go away & I think they would at
> least match if not beat their auto brothers for longevity. I know the closed cooling is an
> "option" but it is priced such that you are perilously close to the same pricing as a
> proper marine diesel, then why not get a proper gearbox/drive & so on & so on.
>
> These things are essentially designed for the rec. boater, down to a price with
> high retail margins built in, to support small seasonal dealers, like alot of other
> hobbies. sporting equip, & other optional expenditure. (Harry saved $2000 in 6,800 & I
> guess the dealer was still happy with the deal)
>
> I guess I sound critical of the I/O but the good news is everything I say is wrong
> with them applies equally to O/Bs, hence I said it's "opinion"
>
> Sorry for any typos.
>
> Karen Smith.
>
> On 27 May 1998 05:14:39 GMT, be...@mail.med.upenn.edu (Marcus G Bell) wrote:
>
> >K Smith (drif...@nospamwebrider.net.au) wrote:
> >
> >> Marcus,
> >
> >> Yes I would agree.
> >
> >We agree that the I/O engine gets a workout, as originally said?
> >
> >This other stuff about comparing the commercial truck engines to
> >commercial inboards was great. I hope we get lots more like it.
> >
> >--
> >--
> >Marcus. ( be...@mail.med.upenn.edu )
>
>
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
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K Smith
Dan,
A bit embarrassed, but I'm afraid I'm probably not much help.
We had lots of AQ115 & AQ120 but not so many AQ125 I have no first hand
experience, regardless my suggestion is;
(i) You say it was re-powered with the AQ125 seems a little old to be new in
88 so I'm assuming it was actually rebuilt in 88.
(ii) On the port side of the motor you'll find a 6 or 8 digit number, give it
to Volvo themselves & they will deffinitely ID it for you, I suspect mid 70s at
latest, so it is old which of itself is not all bad.
(iii) The dreaded manifold/riser question has to be asked, has/when was it
replaced, at the rebuild? they are very expensive (here about $1500).
(iv) It is difficult these days to get a written "appraisal" done on an older
engine/drive, because of the risks & the work to do it properly, so I suggest
you say to the seller that you get it serviced by a reputable independent Volvo
franchise. Try for one on the water so they can have a run in it. (here that
will cost $300-$500 if nothing too bad is found) You pay for the service if all
is well & the sale is completed & you say split the cost if a serious problem
arises such that you don't wish to proceed. A proper service, will check
compressions, replace filters, plugs, tune etc all stuff you will need anyway
but they will also check/service the leg, coupling bellows, uni joint etc, a
good service should be able to talk sensibly about the likely manifold/riser
condition, based on what else they find.
(v) The boat is a 70 model, again not a problem of itself but it's old, so
I'm guessing this is reflected in the asking price. The obvious applies, just
have a real good look at it, take your time & write what you find, play in the
steering, instruments that don't work, tatty wiring hanging,
chipped/scratched/crazing of gelcoat, missing/out of date safety equip., old
battery date stamp, oil leaks, go for a long run & note any excess water
drained from under the floor after, at the least it might help when negotiating
price with the seller.
Sorry I couldn't be of much help.
We'll get into trouble from Marcus, for re-activating such an old thread
he's already got Harry picking up papers in the playground for bagging Skipper.
Karen Smith