Fuel consumption on 54-60' boats
Jaime
I am deciding on the purchase of a 54-60´ boat. The
biggest boat I´ve owned so far is a 38´. I´ve been offered some second
hand boats with all about 4 years.
The reason I am asking here is I have found a Princess
60´ (with twin 800 cats) in good shape and for a good price, but I´m a
little afraid if the maintanance and fuel consumption will be much
higher than that of a 54 with twin 620s (Astondoa, the other boat I
am deciding between). What do you think? Does anybody have numbers
(specially for fuel consumption) to be able to compare the costs? I
have been looking in the web for these numbers, but haven´t found any.
Thank you very much,
Jaime Velasco
HLAviation
>biggest boat I´ve owned so far is a 38´. I´ve been offered some second
>hand boats with all about 4 years.
> The reason I am asking here is I have found a Princess
>60´ (with twin 800 cats)
600 gallons per day econo cruise, 1600 gallons wide open.
>afraid if the maintanance and fuel consumption will be much
>higher than that of a 54 with twin 620s (Astondoa, the other boat I
>am deciding between).
450 econo- 1350 wide open.
This is based on a general rule of thumb of 1 gallon per day per horsepower
produced. Check with the nautical architect for the speed hp. graph for the
boat to find the optimum speed for your needs.
http://hometown.aol.com/hlaviation/
Brian Mitchell
"HLAviation" <hlavi...@aol.com> wrote in message
news:20020412111443...@mb-cl.aol.com...
> > The reason I am asking here is I have found a Princess
> >60´ (with twin 800 cats)
>
> 600 gallons per day econo cruise, 1600 gallons wide open.
Cor - just realised why I have a sailboat :-)
Cheers, Brian
Steve
starts howling).
And I think my little 25 hp diesel does a little better that HLs rule of
thumb. Like 1/2 to 3/4 gal/hr depending on rpm or about 12 gal/day.
Steve
s/v Good Intentions
Larry W4CSC
Flowscans, the ones with two needles pointing towards each other just
to see how high they'll go....(c;
The ragbaggers are gonna LOVE this thread...hee hee.
Larry
Rich Hampel
to $5.00 gallon too..... then let see how you enjoy WOT.
Rick
Specific fuel consumption is the magic term. You can go to the
manufacturer and obtain the specification for "specific fuel
consumption" for a specific engine.
As a rule of thumb a modern high speed diesel will consume anywhere
between .4 to .5 pounds of fuel each hour for each horsepower it
produces. Some engines are better, some are worse but for the type of
information you want a figure for a modern Cat is around .4 lb/hp/hr.
Each of your 800 hp engines should burn about 50 gallons per hour at
maximum output and just over 30 gph at 65 percent power.
The actual figure will depend on the propeller curve since that
determines just how much power the engine delivers at what rpm. You will
need the designer's or builder's sea trial data to narrow it down
further - assuming the propeller pitch or diameter has not been changed.
You may or may not be extracting full rated power at the rpm which
equates to full power on the engine output graph. - If that seems
confusing, just because the engine spins up to "full speed" doesn't mean
that it is fully loaded. Fuel consumption is related more to load than
rpm and the load on your engine at a given rpm will depend on the
propeller.
Rick
Larry W4CSC
>Yeah great..... and I hope and pray that the cost of Marine fuel goes up
>to $5.00 gallon too..... then let see how you enjoy WOT.
>
Shhh....marina operators watch these threads very carefully...(c;
Larry
Jere Lull
He DID say "per HP produced". You're not using all that 25 hp; more
likely 7-12 hp. We have been cruising at .33 gph (about 5 hp) and use
about 5 gallons a day, so I think HLAviation is quoting a rule of thumb
that comes out about right.
>This is based on a general rule of thumb of 1 gallon per day per horsepower
>produced.
>
--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 sailing from Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ annotated pics) http://members.dca.net/jerelull/BVI.html
Jim Hollenback
: "HLAviation" <hlavi...@aol.com> wrote in message
Yeah, but you can't toss a wake like this puppy ;-)
--
Jim Hollenback
jho...@cup.hp.com
my opinion.
Bill Kiene
This is a good example of what is so wonderful about this boating news
group.
Normally, we could never talk to someone like Rick, that has a professional
knowledge of marine engineering, for less than about $100/hour.
I want to thank all the boat people out there that are willing to share
their knowledge with others.
Bill Kiene
"Little boat lover"
"Rick" <tu...@earthlink.net> wrote in message
news:3CB758E3...@earthlink.net...
Jaime
conclusions from your information. I really appreciate it.
Best regards,
Jaime Velasco
Larry W4CSC
wrote:
Don't forget. The dock boys take any credit card, huge piles of cash
and some will take gold bullion if it's stamped "Credit Suisse" on
top....
God I love to pull that Hatteras 56 into the fuel dock and tell the
pump boy to 'FILL ER UP' on my buddy's Platinum card....(c;
Larry
Richard
up to a 30'-34' w/twins. Diesel is very spendy at this price point, and I'm
not impressed with Volvo (Peugeot) or Hino diesels.
I put up an article some time back and got spanked for even suggesting that
the Chev diesel be used to repower older gas boats. So what's the figures
here?
I hear about diesel longivity, but I also hear about way spendy stuff like
starters and minifolds.
Any takers on this topic?
R
<snip>
"Jere Lull" <jere...@BellAtlantic.net> wrote in message
news:3CB76B9A...@BellAtlantic.net...
doug dotson
Is that figure for diesels for a particular type of diesel? I get
1 gph from my 85HP Perkins and I'm pretty sure I'm getting
more than 18HP or so out of it.
doug
"Karl Denninger" <ka...@FS.Denninger.Net> wrote in message
news:a9mknn$k2f$0...@pita.alt.net...
> 1 gph per 10hp actually developed.
>
> If the boat is powered correctly, and is a planing hull, you will cruise
at
> roughly 50-60% of rated power.
>
> So if you have two 300HP gas engines, for example, you would be using
> roughly 150HP (each), or 300HP total, at cruise.
>
> That would translate into about 30gph.
>
> Diesels burn roughly 0.6gph per 10hp actually developed.
>
> --
> --
> Karl Denninger (ka...@denninger.net) Internet Consultant & Kids Rights
Activist
> http://www.denninger.net Cost-effective Consulting
> http://childrens-justice.org SIGN THE UPREPA PETITION TODAY
>
> In article <iazv8.191$Xz.2...@news.uswest.net>,
Karin Conover-Lewis
running at 2000 rpms for 5 knots. Sound about right? Seems like I'm getting
some free "push" from somewhere, but this holds pretty true whether I'm
going up or down the left coast.
--
Karin Conover-Lewis
klc dot lewis at gte dot net
1963 Rawson 30 ketch "Escapade"
"Karl Denninger" <ka...@FS.Denninger.Net> wrote in message
news:a9nhfa$nqc$0...@pita.alt.net...
> All diesels.
>
> If you're burning 1gph then you're pulling only about 18-20hp out of it -
> believe it or not.
>
> (There is only so much energy in the fuel, and volumetric efficiency is
one
> of those things you can't do much about. Computer control is primarily
> about emissions and controlling fuel waste at low throttle settings, not
> top-end efficiency.)
>
> --
> --
> Karl Denninger (ka...@denninger.net) Internet Consultant & Kids Rights
Activist
> http://www.denninger.net Cost-effective Consulting
> http://childrens-justice.org SIGN THE UPREPA PETITION TODAY
>
> In article <d7Bv8.16583$A%3.14...@ord-read.news.verio.net>,
Rick
Perhaps you meant thermal efficiency. Volumetric efficiency is one of
the few parameters that designers can do a great deal about. Simply
adding a turbo or a scavenging air blower (ala GM) can put volumetric
efficiency above 100 percent.
This discussion of quarts and gallons per hour is a waste of time since
even if all parties are talking about the same gallon the number of
BTU's in that gallon will vary considerably with temperature. Very few
small boat operators really know how much power their powerplant
produces at any given rpm, the information they need to determine that
is not readily available to most small boat users.
How many here have shaft horsepower meters installed? How many have a
torque meter installed? How many know the propeller curve for their
installation? How many have bothered to check the documentation for
their engines or contact the manufacturer and simply ask what the brake
specific fuel consumption figure is for their engine?
It is amazing to me that there is so much effort spent on ridiculous
home-made specifications like "gallons per 10hp per hour." The real
figure exists, the manufacturers are pleased to supply it and the figure
is accepted world wide as a valid engineering unit. The number enables
apples to apples comparisons. Most boaters are happy to use knots and
fathoms, why is there so much resistance to using legitimate, and
universal, engineering units when talking about fuel consumption?
Lacking the instrumentation to measure instantaneous horsepower output,
if fuel consumption metering is installed, a boater with the engine
manufacturers brake specific fuel consumption figure can use that
information to closely approximate the horsepower produced at a given
rpm. You guys are trying to work backwards without a real starting
point.
Rick
Karin Conover-Lewis
I don't know about anyone else, but I've been trying to find an owner's
manual for my engine since I bought the boat in December, and have yet to
find one. My engine is a 1979 Universal 5416, which is obsolete. Two other
engines have replaced it, but they are not the same engine regardless of how
similar they may be. Don't shoot people for trying to find whatever scrap of
information that might be available, okay?
And I must take exception with the idea that engineering terms like "BTU's
per hour per torquemada unit (g)" are more useful, to the average boater in
real life, than "So many quarts (or gallons) per hour at a given engine
rotation speed." Maybe it will turn out to be a little different at
different temperatures -- but a base figure upon which to make simple
estimates is not unreasonable. Maybe shaft RPM's (or actual torque) would be
a better constant for such estimates -- but I don't know of any boats which
have shaft speed (or torque) gauges. Mine sure doesn't.
--
Karin Conover-Lewis
klc dot lewis at gte dot net
1963 Rawson 30 ketch "Escapade"
"Rick" <tu...@earthlink.net> wrote in message
news:3CBF7BAC...@earthlink.net...
Rick
>at a given engine rotation speed."
That is a valid number only if you obtained it from another operator of
the same hull of essentially the same weight with the same engine,
reduction gear and propeller installed.
Trying to calculate "a boat's" future fuel consumption based solely on
the max rated horsepower of the installed engine with no regard for any
other factor is a waste of time.
I stated very clearly that the only valid number available for the vast
majority of boaters is the engine manufacturer's specification for brake
specific fuel consumption. If it is not in the engine manual it may be
obtained from the manufacturer, if the manufacturer is no longer in
existence and the number is unavailable then you can use the general
figure of .4 lb/hp/hr and use 7 pounds per US gallon (at around 60
degrees F) and a fuel flow totalizer to determine the power output of
your engine in your boat at whatever rpm you collected the data.
Asking someone on the internet how much fuel your engine burns or how
much power it produces in your boat is a pointless exercise unless, as I
stated, you ask the operator of an identical vessel.
You may not find the use of BSFC "useful" but it is the only figure you
have available to reduce the gallons burned in real life to a measure of
the power needed to move your boat at a given power setting. If you
record the fuel burned and the time at a given rpm and repeat the
exercise at different power settings, you can then develop a graph of
the power output vs fuel consumption vs boat performance at various
rpms. Then you will have real numbers which apply to your boat and your
powerplant.
Rick
Karin Conover-Lewis
If you will note, I did not *ask* anyone what my engine burned, I *stated*
it. Approximately one quart per hour at 2000 rpms, which yields 5 knots
average speed over ground (without unusual currents). My question whether or
not that sounded about right. I would like to know how it compares with
other's experience, whether that makes sense to you or not. I have also
stated that I don't have a manual, and that I am looking for one but can't
find it. I will continue looking. But that I have not looked it up is hardly
a failing on my part.
Sorry that this question annoys your inner engineer. ;-)
--
Karin Conover-Lewis
klc dot lewis at gte dot net
1963 Rawson 30 ketch "Escapade"
"Rick" <tu...@earthlink.net> wrote in message
news:3CBF88DE...@earthlink.net...
Rick
What you got is what you got for your boat. No one else except the
operator of an identical boat could possibly answer your question. No
one else can say that your number is "right" or not, who knows, you
might have a watermaker pump that consumes 15 hp attached to a PTO on
the engine.
The subject line tells it all. Someone wanted to compare the fuel
consumption between two boats with different engines, the only number
anyone, aside from the operator of the specific boat in question, could
possible provide a meaningful response. The only information anyone else
could provide would be the BSFC of the particular engines installed. How
much power the boat absorbs at a given rpm could be calculated after
measuring the actual fuel consumption. Or, if the actual power consumed
at a given rpm is known then fuel consumption could be calculated for a
given power setting.
>"I did not *ask* ..."
I tried to show that with the information you have and the BSFC figure
you can calculate the horsepower used at the power setting which burned
the gallons/quarts you measured.
You did ask if the figure you gave was "about right." Again, only the
operator of an identical boat can tell you if it is "about right" or at
least similar for that installation, no internet diesel guru can tell
you. If you want to know how much power that represents or if your
efficiency is anywhere near "normal" then you need more information.
My "inner engineer" and my outer one cringes at posts which purport to
provide information based on homemade terms that have no foundation in
fact or application or which claim to tell a poster what kind of
performance should be expected from an unknown system.
Rick
Karin Conover-Lewis
Exactly the sort of information I was looking for -- thanks! Still trying to
track down a manual for the engine, but I don't have much hope of actually
finding one. I'm sure that the manual would have a power and fuel
consumption curve in it, somewhere. As it stands right now, it seems to be
running a little hot (though not smoking at all, and plenty of water is
going through it) and I'm going to have a diesel-type look it over. I won't
feel good about running it at higher rpm's until I know it's operating in
the right temperature range.
--
Karin Conover-Lewis
klc dot lewis at gte dot net
1963 Rawson 30 ketch "Escapade"
"Karl Denninger" <ka...@FS.Denninger.Net> wrote in message
news:a9o4d8$l8$0...@dosa.alt.net...
> Yep. You're probably only pulling about 5-6hp out of it at 2000 RPM.
>
> Prop demand curves are pretty much logrythmic things. At 1900 RPM I pull
> about 270 HP per engine out of my 500HP diesels and burn 32 gph. At WOT
> (2300) I guzzle nearly 60 gph!
>
> I'm at 82% of maximum RPM but at only 54% of output. You're at 69% of
> maximum RPM and I bet you're pulling no more than 33% of maximum output.
>
> --
> --
> Karl Denninger (ka...@denninger.net) Internet Consultant & Kids Rights
Activist
> http://www.denninger.net Cost-effective Consulting
> http://childrens-justice.org SIGN THE UPREPA PETITION TODAY
>
> In article <c3Iv8.6198$93....@nwrddc04.gnilink.net>,
Rick
>between different diesel engines."
Anywhere from .25 (or even less on some new slow speed engines) to .5,
that's a fair degree of variation but irrelevant to this discussion. I
suggested the average small boater can use .4 and find satisfaction with
the results.
>"Oh sure, there is some variation, but nowhere near the kind of
>claims that I've seen."
I don't know what you have seen but the installed specific fuel
consumption will be slightly greater than the manufacturer's published
BSFC because that does not include the power used to drive the reduction
gear, the raw water pump, alternator, or other engine driven
auxiliaries. That is why the .4 figure or even a .5 figure works as a
ballpark number for small engine installations, it includes all the
power produced in less than a perfect installation, not just that
delivered to the propeller.
>"If you run to maximum RPM at maximum throttle and do NOT hit
>the governor then you are getting all the power your engine is
>capable of delivering at that RPM. If the engine turns up to the
>rated RPM you can reasonably assume you're getting maximum output ..."
That is a bit simplistic and possibly misleading. The throttle control
adjusts the speeder spring on a simple speed limiting governor so the
governor is always "hit." If the governor has not reduced the fuel by
way of an overspeed limiter then a different condition exists. If you
have a torque limiting governor that is a different matter as it will
reduce fuel at a certain load regardless of the rpm. If the engine turns
up to the rated rpm then all you can assume is that it is not
overloaded. If max rated rpm is reached the engine is only producing the
horsepower that is consumed by whatever is attached to the output shaft.
It may or may not be the maximum rated power.
Rick
doug dotson
at 6 kts and run refrigeration and the entire electrical
system of the boat on only 18HP.
doug
"Karl Denninger" <ka...@FS.Denninger.Net> wrote in message
news:a9nhfa$nqc$0...@pita.alt.net...
> All diesels.
>
> If you're burning 1gph then you're pulling only about 18-20hp out of it -
> believe it or not.
>
> (There is only so much energy in the fuel, and volumetric efficiency is
one
> of those things you can't do much about. Computer control is primarily
> about emissions and controlling fuel waste at low throttle settings, not
> top-end efficiency.)
>
> --
> --
> Karl Denninger (ka...@denninger.net) Internet Consultant & Kids Rights
Activist
> http://www.denninger.net Cost-effective Consulting
> http://childrens-justice.org SIGN THE UPREPA PETITION TODAY
>
> In article <d7Bv8.16583$A%3.14...@ord-read.news.verio.net>,
> doug dotson <ddo...@digidata.com> wrote:
doug dotson
> Doesn't surprise me all that much.
>
> BTW, my 8kw generator has a 14HP Yanmar engine - fairly "new" technology
as
> far as these things go. It pulls about 0.8gph at full load. In real,
> typical use on the water over a full day's use its well under half of
that.
My new 4.2Kw generator has a 7.65HP Ferriman engine and reportedly burns
1/6 gph at half load. Don't have enough empirical evidence yet to know
how it actually does. Sounds in the same ballpark though.
> Your figure doesn't surprise me all that much, particularly for a sailing
> vessel in good conditions.
When we measured the fuel consumption most of the time we were motoring
in good conditions. Heading up the coast we did 22 hrs into 20kt headwinds
and 4 ft seas so it was working a bit harder and a little slower, maybe 5 to
5.5 kts. Overall we motored 73 hours on 72 gallons. Same RPMs the
total time.
> What RPM do you turn up to, what RPM are you typically running at with
this
> consumption.
The tach says 2500 but it is wrong. When we first bought the boat the survey
measured the speed with an optical tach at a few speeds and I made up a
graph to convert from indicated to actual. I believe we run at 1800 or so
but I'd have to check.
> and if you take the engine out of gear what is the no-load
> full-throttle RPM? That will shed quite a bit of light on what you're
> actually pulling out of the engine.
Don't know that one. Might be in the initial survey as well. I need to
fix that tach at some point.
> --
> --
> Karl Denninger (ka...@denninger.net) Internet Consultant & Kids Rights
Activist
> http://www.denninger.net Cost-effective Consulting
> http://childrens-justice.org SIGN THE UPREPA PETITION TODAY
>
> In article <J7Uv8.16663$A%3.14...@ord-read.news.verio.net>,
Rick
>what you're actually pulling out of the engine."
A pretty dim light. Please explain what this will indicate other than
the governor high speed setting?
If the engine is out of gear the only power developed will be that
required to rotate the engine, its auxiliaries, and the input side of
the reduction gear.
Stick to your computer consulting, Karl. Most of what you have posted in
this thread is nonsense or applies only to your specific engine and
boat. You have learned a bit of the vocabulary but your understanding of
marine diesel propulsion systems leaves much to be desired for someone
so ready to dispense advice to all comers.
Rick
Richard
15% error for drag and windage in real world conditions -- to my actual
mileage.
24' planing hull. On step @ 18 mph, cruise @ 26, top out @35. 200hp gas,
burns about 10-12 gph cruise, 18-19 flat out. There is a 'sweet spot' on
planing, near full throttle, where the boat seems to like to run, but you
can't run it there for long, it's about 3900-4100 rpm, just too fast for a
safe (wear and tear wise) cruise.
I fiddle witht the prop, tabs and fins every year, prior to launch, and it
gets a little better. When I get real close to optimum, I can go with a SS
prop for the last little bit of push.
R
<snip>
"Karl Denninger" <ka...@FS.Denninger.Net> wrote in message
news:a9nhfa$nqc$0...@pita.alt.net...
> All diesels.
>
> If you're burning 1gph then you're pulling only about 18-20hp out of it -
> believe it or not.
>
> (There is only so much energy in the fuel, and volumetric efficiency is
one
> of those things you can't do much about. Computer control is primarily
> about emissions and controlling fuel waste at low throttle settings, not
> top-end efficiency.)
>
> --
> --
> Karl Denninger (ka...@denninger.net) Internet Consultant & Kids Rights
Activist
> http://www.denninger.net Cost-effective Consulting
> http://childrens-justice.org SIGN THE UPREPA PETITION TODAY
>
> In article <d7Bv8.16583$A%3.14...@ord-read.news.verio.net>,
> doug dotson <ddo...@digidata.com> wrote:
doug dotson
did during the sea trial to determine of the boat was propped
properly.
doug
"Rick" <tu...@earthlink.net> wrote in message
news:3CC03B46...@earthlink.net...
Rick
Karl did:
>"... if you take the engine out of gear what
>is the no-load full-throttle RPM?"
I will address that and the rest of the issues in a post later today.
I have to go suck some union wages out of the economy. <G>
Rick
doug dotson
Jere Lull
>I just find it amazing that I can push 25,000 lbs of boat
>at 6 kts and run refrigeration and the entire electrical
>system of the boat on only 18HP.
>
>doug
>
Yeah, ain't it great! Displacement hulls are quite efficient,
particularly considering the "draggy" medium they operate in. That 6
knots is well down from your hull speed. If you pushed it at 90+% of
hull, your mileage would definitely degrade.
In our case, we burn a quarter of a gallon an hour at about 5.5 knots, a
third of a gallon at 5.8, with only a 200 rpm change. It feels good to
get 25 mpg with a 7000+# vessel, though I worry a bit that we're only
using a quarter of rated output -- seems we might be loading the engine
too lightly.
Rick
Karl wrote:
>"... if you take the engine out of gear what is the no-load
>full-throttle RPM? That will shed quite a bit of light on
>what you're actually pulling out of the engine."
Rick:
>Please explain what this will indicate other than
>the governor high speed setting.
Karl:
>"That you're not running into it provided the full-load
>RPM is significantly lower (it usually is)"
When the engine stabilizes at the no-load full-throttle rpm it does so
precisely because the governor limits the speed to its high speed
setting. It is "running into it" - whatever that is supposed to mean. As
a matter of fact, the limiting rpm will be reached long before the
throttle reaches its mechanical stop if no load is connected to the
engine.
A governor is not a third party that just sits passively on the sideline
until it is called into play by overspeed or some other mysterious
parameter. In the simple speed limiting flyball governor as fitted to
most small diesels, the throttle lever adjusts a speeder spring in the
governor and this sets the engine rpm. If rpm drops due to an increased
load the governor will increase the fuel admitted to the engine,
increasing the power to match the new load. As the load is taken up the
engine speed will return to the previously set speed. This engine may
only be producing 30 percent of its rated load or speed but it is "on
the governor" or "running into it" or whatever euphemism you choose to
use. The governor manages all the speed control all the time.
Karl:
>"... If you are UNDERPROPPED, you will run into the governor."
If you are "underpropped" you will not deliver all the available
horsepower to the water. The engine will easily reach the high speed
limit setting on the governor at less than full "rack" or maximum volume
of fuel flow, just as it will if not in gear. The engine can't "run
into" the governor, it was already governed from idle all the way up to
the high speed limit.
If the boat is "propped" correctly, the propeller will operate at its
most efficient speed at around 80 percent of the engine's max rated rpm.
If an engine is selected which has sufficient power to provide the
desired cruise speed at about 80 percent rpm then a reserve of power
will be available to compensate for weather or other transient needs by
increasing rpm to the max rated speed. So a carefully
matchedboat/propulsion system should allow the engine to reach max rated
or governor limited rpm. Best cruise speed will still leave some
throttle travel available. If the rpm's stop increasing before the
governor's high speed limit or full rated rpm (they can be and probably
are different) is reached the engine is overloaded or "over propped."
Rick:
>If the engine is out of gear the only power developed will be that
>required to rotate the engine, its auxiliaries, and the input side of
>the reduction gear.
Karl:
>"Correct. Measuring that is not the point of such a test."
Well then, what IS the purpose of this "test" ?
Karl:
>"You continue to preach about the need to get figures that some people
>simply don't have (particularly propellor demand curves) and that analyzing
>engine output and fuel burn without them is impossible."
Where do you get that idea? Perhaps a review of my statements is in
order:
>Very few small boat operators really know how much power their powerplant
>produces at any given rpm, the information they need to determine that
>is not readily available to most small boat users.
>Lacking the instrumentation to measure instantaneous horsepower output,
>if fuel consumption metering is installed, a boater with the engine
>manufacturer's brake specific fuel consumption figure can use that
>information to closely approximate the horsepower produced at a given
>rpm.
Even if that metering is just recording how much fuel you bought vs how
long you ran at an average rpm.
>the only valid number available for the vast majority of boaters
>is the engine manufacturer's specification for brake specific
>fuel consumption.
>it is the only figure you have available to reduce the gallons
>burned in real life to a measure of the power needed to move your
>boat at a given power setting.
>If you record the fuel burned and the time at a given rpm and repeat the
>exercise at different power settings, you can then develop a graph of
>the power output vs fuel consumption vs boat performance at various
>rpms. Then you will have real numbers which apply to your boat and your
>powerplant.
That graph is - ta da - a propeller curve! A boat owner armed with a
tachometer and the BSFC of the engine can develop a rare and mysterious
chart that will make "analyzing engine output and fuel burn" very simple
and possible for most boaters who care to understand their systems. Now,
what part of all the above was "preach(ing) about the need to get
figures that some people simply don't have ...?"
>I stated very clearly that the only valid number available for the vast
>majority of boaters is the engine manufacturer's specification for brake
>specific fuel consumption. If it is not in the engine manual it may be
>obtained from the manufacturer, if the manufacturer is no longer in
>existence and the number is unavailable then you can use the general
>figure of .4 lb/hp/hr and use 7 pounds per US gallon
Karl:
>"Applying the 0.6gph/10hp figure to this, ..."
That equates to about .42 lb/hp/hr IF the gallons are US gallons. You
could have stated it in terms of cubic station wagons per lunar
occultation per kilowatt if you chose, they are all valid measures but
when you write about boats you use nautical terms, when you write about
engines then use engine terms. Boaters, especially sailboaters, love to
use bizarre ratios of waterline to halyard diameter and such in an
attempt to be able to compare apples to apples, why then is it so
difficult to use universally recognized measures when discussing engine
performance? Most new engine spec sheets provide the SFC figures in
metric units, grams/kilowatt/hr, so that everyone in the world has the
same unit of measure.
Karl:
>"Nobody in a recreational application has engines burning bunker fuel,
>for example, so the variability that you're indicating that includes
>such applications simply does not apply."
>"BSFC numbers are not widely different between different diesel engines."
Rick:
>Anywhere from .25 (or even less on some new slow speed engines) to .5,
>that's a fair degree of variation but irrelevant to this discussion. I
>suggested the average small boater can use .4 and find satisfaction with
>the results.
And what has any of that got to do with bunker fuel or anything else? It
showed that there is indeed a wide variation in specific fuel
consumption among different diesel engines (contrary to your statement)
and included the disclaimer that for the readers of this newsgroup the
lower extremes are irrelevant.
Karl:
>"There are only so many BTUs per pound of fuel consumed. There are limits
>to the efficiency of conversion imposed by the fact that you exhaust hot
>gas (the thermal energy that goes out the exhaust, or that which you
>radiate away from the heat exchanger, or that which is rejected into the
>engine room, is energy you LOST!)"
And spherical objects may appear round when viewed in sunlight. A truism
but what has that got to do with anything? It comes across like a
smokescreen of useless and incomplete information added to obfuscate the
issue under discussion.
Karl:
>""medium speed" diesels with WOT ranges in the 2300-2500 rpm arena ..."
That is a high speed diesel, Karl. Medium speed is generally between 400
and 1000 rpm. If you are going to talk the talk at least try and get it
right.
Rick
Rick
>"Which you may not have."
Read the paragraph again, Karl. If a boat operator calculates hp vs rpm
and fuel flow he will generate a propeller curve. Why are you having
such a difficult time with this concept? How can I make it simple enough
for you to understand?
>"Determining if the full-load and no-load RPMs are the same.
>If they are you may well be underpropped."
Or perfectly propped. You cannot tell another boat operator if it is or
is not without more information. And that is precisely why I am
bothering to write this stuff, it bugs me to see people giving bad or
ill founded advice on subjects which they themselves lack a sound
understanding.
>"Most engines are rated DIFFERENTLY under load and no-load in
>terms of RPM expected. As an example, mine are rated at 2300 RPM
>full-load, but 2500 RPM *NO LOAD*."
Your engines are rated to produce X hp at Y rpm. Your boat is propped to
extract power from the engine at an rpm that is lower than the maximum
rated rpm because (forgive me for having to enter this into the
discussion as it will lead you to who knows where) the torque is higher
at less than maximum rpm and that is the speed where your propellers are
at their most efficient. If you cannot exceed 2300 rpm with those props,
unless you have torque limiting governors you "may" be "overpropped." If
the engines cannot spin up to develop their full rated horsepower which
occurs at a higher rpm than the max torque and the rpm at which the
propeller is most efficient, there is a mismatch somewhere. Have you
been doing your own maintenance? The 2300 rpm figure is a design
compromise between fuel efficiency and cruise power. Your boat may be
slightly underpowered or at least it might benefit from more horsepower
so that you can cruise at a high power that is comfortably less than the
maximum available. This will equate to longer engine life. These may be
subtleties that are beyond your level of understanding, Karl, but they
exist and you can, if you stop posting nonsense long enough, learn the
art.
>"Not in recreational applications its not."
Karl, a 2300 rpm diesel is a high speed diesel no matter where it is
installed. Just like all the other terms you refuse to acknowledge or
use a high speed diesel is one that is universally accepted by
manufacturers and engineers the world over as one which operates above
1000 rpm. A medium speed diesel is one which operates between about 400
and 1000 rpm. A slow speed diesel is one which operates up to 200 rpm,
the speed range between 200 and 400 is up for debate as to slow or
medium. If you will not believe me then please ask any manufacturer of
diesel engine for a catalog of their medium speed diesels, commercial or
recreational. Let us know what you receive.
>"Find me someone with a 400-1000 RPM diesel in a boat under 100
>feet in recreational service."
>"Good luck"
No "luck" required, I and several of my friends and acquaintances do
just that. We own and operate old converted tugboats and vintage yachts.
For many years most larger motor yachts were powered by medium speed
diesels. Like I said, Karl, if you want to talk the talk try and get it
right.
>"(The issue there ends up being displacement and, more precisely,
>reciprocating mass and stroke. As they increase the maximum rational
>RPM comes down. However, weight goes WAY up for the engine.)"
WTF are you talking about? What has this got to do with the topic? Are
you reading some diesel book and feel a need to paraphrase something
from Chapter 1? Stay on topic and stop "smokestacking."
Rick
Rick
Nice job of editing out the yacht(s) part ... was that an attempt to
prove something?
>"For diesels, such flow meters can cost many thousands of dollars.
>For example, to put flowscans on my twin diesels would cost me over
>$4,000 in PARTS. That does NOT include installation!"
Geez, Karl, that doesn't seem to have stopped you or anyone else in this
thread from calculating their fuel consumption down to the pints per
hour ... first you claim precise knowledge of your fuel consumption
across a wide range of speeds and now you claim it is too costly to
obtain fuel flow data. Make up your mind. Does the statement "Even if
that metering is just recording how much fuel you bought vs how long you
ran at an average rpm" sound familiar to you? I wrote that so other
readers would not think an expensive fuel flow totalizer was the only
way to obtain the data.
>"But if you don't, and most smaller (or older) engines don't, then
>you cannot get ACCURATE numbers easily."
Make up your mind, Karl. In other posts you even cited the fuel
consumption for your generator down to the tenth of a gallon. You stated
various fuel flows for your boat at varying percentages ... now you
claim: "... you cannot get ACCURATE numbers
easily." Which one is it Karl, are you the only one who can generate
good numbers or are you just reading some paperwork that came with your
boat? I don't think you KNOW how much power your props absorb or how
much power your engines produce at a given rpm in your boat. So far your
last post has contradicted nearly everything you wrote earlier ... which
of your posts are we to believe Karl, the last one or the others?
>"Oh, so the mass of the engine doesn't matter?"
Not in the least for the purposes of this discussion. Stick to the
topic.
>"Stop trying to make this tougher than it is with technical details that,
>while correct, are not necessary to answering the question - which is
>what kind of fuel consumption you can expect and what a given fuel
>consumption implies about the power actually developed by your engine(s)."
Oh, you mean things like the mass of the engine or rotational speed and
stroke? Karl, do you even read your own writing?
You've obviously reached the limits of your ability to rationally
discuss this issue. There is little to gain by beating up on you about
this stuff since it is embarrassingly clear that your understanding of
the subject is very shallow. Good night, Karl.
Rick
Rick
>little to zero application to recreational boaters (converted tugs
>and the like) is beyond silly - its an attempt to obfuscate with
>corner cases that are irrelavent to virtually ALL of those who want
>that information, INCLUDING MOST SPECIFICALLY the person who originally
>asked the question!"
Sure, Karl, you're right, you're an expert. You have done an excellent
job of showing your competence in this thread. There is little more I
can add to your excellent paragraph above.
Rick
doug dotson
"Jere Lull" <jere...@BellAtlantic.net> wrote in message
> doug dotson wrote:
>
> >I just find it amazing that I can push 25,000 lbs of boat
> >at 6 kts and run refrigeration and the entire electrical
> >system of the boat on only 18HP.
> >
> >doug
> >
> Yeah, ain't it great! Displacement hulls are quite efficient,
> particularly considering the "draggy" medium they operate in. That 6
> knots is well down from your hull speed. If you pushed it at 90+% of
> hull, your mileage would definitely degrade.
I'm sure. Hull speed in this boat is around 8.5 but if I push it up
that far under motor you can suret tell it is working harder. During
the sea trials we ran it full throttle for several minutes. Threw out
a pretty impressive wake. Felt like we could have skied behind it.
> In our case, we burn a quarter of a gallon an hour at about 5.5 knots, a
> third of a gallon at 5.8, with only a 200 rpm change. It feels good to
> get 25 mpg with a 7000+# vessel, though I worry a bit that we're only
> using a quarter of rated output -- seems we might be loading the engine
> too lightly.
25 MPG is nice compared to our 6. Always bugs me that our car gets
50.
Rick
Turbo Jetta? Hybrid?
Rick
doug dotson
Rick
275k miles on the first one with original turbo. Only sold to get the
new version turbo Jetta TDI. Could never quite get 50 mpg, 48+ but
couldn't quite make that extra mile. And for the cynics, those were US
gallons of #2 diesel and statute miles. Got a little less mileage on
Jet-A.
The new VW diesels are fantastic machines. Instant start, no vibration,
great performance. Have you tried any other VW diesels?
Rick
doug dotson
> Great cars. I never had a Golf but am on the second turbo Jetta. We got
> 275k miles on the first one with original turbo. Only sold to get the
> new version turbo Jetta TDI. Could never quite get 50 mpg, 48+ but
> couldn't quite make that extra mile. And for the cynics, those were US
> gallons of #2 diesel and statute miles. Got a little less mileage on
> Jet-A.
Ours is a TDI. Pretty phenominal engine IMHO. Never thought of
burning jet fuel in it.
> The new VW diesels are fantastic machines. Instant start, no vibration,
> great performance. Have you tried any other VW diesels?
Not personally. Had a several friends with diesel Rabbits back in the
70's and 80's. They were kind of problematic when the weather got cold,
but the TDI doesn't miss a beat.
> Rick
Lloyd Sumpter
I was looking at older VW diesels and wondering...Far Cove's engine is
getting pretty tired, and it's underpowered from the start (21hp for 36
ft). I COULD get a 25hp Westerbeke for $10K or so (plus installation), or
I could get a VW Rabbit diesel for $1K, toss the car, rebuild the engine,
and have 50hp (and probably about $5K in my pocket...).
Anybody used a VW diesel in a boat?
Lloyd Sumpter
"Far Cove" Catalina 36
Evan Gatehouse & Diane Selkirk
Lloyd Sumpter <lsum...@shaw.ca> wrote in message
> I was looking at older VW diesels and wondering...Far Cove's engine is
> getting pretty tired, and it's underpowered from the start (21hp for 36
> ft). I COULD get a 25hp Westerbeke for $10K or so (plus installation), or
> I could get a VW Rabbit diesel for $1K, toss the car, rebuild the engine,
> and have 50hp (and probably about $5K in my pocket...).
>
> Anybody used a VW diesel in a boat?
Yeah, they were (are) known as Pathfinders. Didn't really have a stellar
reputation if I recall...
--
Evan Gatehouse
doug dotson
you attend a diesel clinic. Last clinic I went to included a guy
who had one. He was not a happy camper.
I heard that Westerbeke doesn't actually make engines, they
just marinize engines made by other companies. I believe the
current models are Mitsubishi engines but years ago a WV
engine may have been the one. They just pick whatever
engine they can get in quanity and inexpensive.
doug
"Evan Gatehouse & Diane Selkirk" <cei...@prodigy.net> wrote in message
news:Lp3x8.5246$1d4.26...@newssvr16.news.prodigy.com...
Rick
What are the complaints about? Are the problems with the engine itself
or the marinization bolt-ons?
Rick
doug dotson
is one of the best diesel guys around from what I hear and the
one that taught the clinic. I hear he has retired and his son is
running the business now. Maybe someone out there can
remember the name of the business and you can talk to them
directly.
doug
"Rick" <tu...@earthlink.net> wrote in message
news:3CC569DA...@earthlink.net...