Bowrider weight
Rick Haslip
I'm thinking of buying a fairly small boat for skiing, fishing and
shoreline camping. The lake we generally camp on is fairly deep and there
are areas on shore where I can glide up right to the beach for disembarking. I
have to be careful when doing this because a few feet on either side of the
'safe' approach line are some submerged rocks. This isn't a real problem
when using our 15 foot aluminum boat and 15hp motor, but could be scary
with a fiberglass hull.
My real question is weight. My car has a towing capacity of about 2200
pounds and I'd always be towing the boat to the lake for the day.
There is a boat launch but no docking facilities on this lake. I'm
looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
appropriate trailer. The boat needs to be able to carry 3 people plus my
dog. Does anyone have an estimate of how much this setup would weigh
(minus the humans and dog)? If this is too much for my car to handle, I'll
have to re-think the type of boat I can get.
Thanks.
Rick.
David James Miller
|>
|> I'm thinking of buying a fairly small boat for skiing, fishing and
|> shoreline camping. The lake we generally camp on is fairly deep and there
|> are areas on shore where I can glide up right to the beach for disembarking. I
|> have to be careful when doing this because a few feet on either side of the
|> 'safe' approach line are some submerged rocks. This isn't a real problem
|> when using our 15 foot aluminum boat and 15hp motor, but could be scary
|> with a fiberglass hull.
Why limit yourself to fiberglass?
|>
|> My real question is weight. My car has a towing capacity of about 2200
|> pounds and I'd always be towing the boat to the lake for the day.
|> There is a boat launch but no docking facilities on this lake. I'm
|> looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
|> appropriate trailer. The boat needs to be able to carry 3 people plus my
|> dog. Does anyone have an estimate of how much this setup would weigh
|> (minus the humans and dog)? If this is too much for my car to handle, I'll
|> have to re-think the type of boat I can get.
I think you're a little over 2K towed weight for most packages that are
fiberglass/OB in the 17' range. Some tend to be lighter (Bayliner - both the
boat and the trailer are light) while some tend to be heavier (4Winns).
Have you considered aluminum boats in this range? They're much lighter than
fiberglass, and require smaller engines and therefore even less weight.
My 17' 4Winns, on it's shorelander trailer with 115HP OB, with gear, is around
2500 pounds. A Volvo wagon rated for 3300 pounds couldn't take steep grades,
and was shakey while towing. On the other hand, the Suburban can pull it
up anything, at reasonable speed, and doesn't shake one bit :) Bottom line,
I'd try to stay under the tow capacity by a reasonable margin.
Dave
--
David James Miller Delivery Systems Architecture
Mead Data Central, B6F3 (513) 865-7441
PO Box 933 dav...@meaddata.com
Dayton Ohio 45401 I speak for me, not MDC
Rick Haslip
In a previous article, dav...@meaddata.com (David James Miller) says:
>In article <CDCML...@freenet.carleton.ca>, ad...@Freenet.carleton.ca (Rick Haslip) writes:
>|>
>|> I'm thinking of buying a fairly small boat for skiing, fishing and
>|> shoreline camping. The lake we generally camp on is fairly deep and there
>|> are areas on shore where I can glide up right to the beach for disembarking. I
>|> have to be careful when doing this because a few feet on either side of the
>|> 'safe' approach line are some submerged rocks. This isn't a real problem
>|> when using our 15 foot aluminum boat and 15hp motor, but could be scary
>|> with a fiberglass hull.
>
>Why limit yourself to fiberglass?
Purely ignorance on my part. I didn't know an aluminum boat might fit the
bill. I guess I automatically associate aluminum boats with small ugly
fishing boats. My mistake. Any opinions or advice on aluminum boats is
very welcome indeed.
>|> My real question is weight. My car has a towing capacity of about 2200
>|> pounds and I'd always be towing the boat to the lake for the day.
>|> There is a boat launch but no docking facilities on this lake. I'm
>|> looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
>|> appropriate trailer. The boat needs to be able to carry 3 people plus my
>|> dog. Does anyone have an estimate of how much this setup would weigh
>|> (minus the humans and dog)? If this is too much for my car to handle, I'll
>|> have to re-think the type of boat I can get.
>
>I think you're a little over 2K towed weight for most packages that are
>fiberglass/OB in the 17' range. Some tend to be lighter (Bayliner - both the
>boat and the trailer are light) while some tend to be heavier (4Winns).
>Have you considered aluminum boats in this range? They're much lighter than
>fiberglass, and require smaller engines and therefore even less weight.
(stuff deleted)
I guess my next question is what size outboard engine would be required on
a 17-18 foot aluminum boat to ski, etc. and how much may a package such as
this weigh? Any suggestions on makes, models?
Thanks for the advice.
Rick.
Bob Rusk
>My real question is weight. My car has a towing capacity of about 2200
>pounds and I'd always be towing the boat to the lake for the day.
>There is a boat launch but no docking facilities on this lake. I'm
>looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
>appropriate trailer. The boat needs to be able to carry 3 people plus my
>dog. Does anyone have an estimate of how much this setup would weigh
>(minus the humans and dog)? If this is too much for my car to handle, I'll
>have to re-think the type of boat I can get.
If you go aluminum, you can drop down to an 80-90 hp motor witih the same
performance. My old 16' aluminum Starcraft bowrider with an 85 hp motor
weighed less than 1500 lbs on the trailer and would reasonably carry 6 people.
I could slalom behind it with a 50 hp motor, and the 85 would pull a 250 lb
friend up from a deepwater slalom start. My Starcraft's hull weight was ~650
lbs. Don't knock it 'till you try it -- mine stood up to 11 summers' hard use
by teenagers before I sold it. It still had no leaks, but was ready for some
work. Today I would look at Lowe, Lund, Sea Nymph, and maybe a couple of
others.
Many fiberglass boats will still squeak in under your weight limits. Watch
out, though, as many boats of this size are pretty heavy. I figure you want
to keep the hull weight under 1200 lbs on a lightweight trailer and under 1000
lbs on a heavy one. I've been amazed to see 15' fiberglass runabouts that
weighed more than that, while my Dad's 17' Boston Whaler has a hull weight
of ~950 lbs.
--
Bob Rusk
rr...@ssd.csd.harris.com
My thoughts, probably not Harris'.
acss...@acs.eku.edu
I would think you could find something that would fit that bill, but you
might have to sacrifice something else (freeboard, ride, taking guests,
storage space, etc.). For instance, a 17 ft. Checkmate Diplomat with a
115 outboard would probably be close to perfect. There seem to be alot of
them for sale in this area. They are fast, low freeboard boats though
still deeper that bass boats. They seat 6 comfortably for a ride, but
unless you are going a shore, I wouldn't take more than 4 for a whole
day. Also, something from Baja in the early to mid 80s would probably be
ok. If you want brand new Baja could and probably would build something from
previous model years that would suit you as well. And there is the
possibility of almost any 15-17ft. dual console bass boat, if that's
your sort of thing? Anyway, I think you have some options...
Dudley Cornman
acss...@acs.eku.edu
Mark Crafts
I think many bowriders, especially if they're I/O will exceed that weight.
OTOH, I had a 17' Wahoo (clone to the Boston Whaler Montauk) with a 90 hp
outboard on the back, that - with the trailer, weighed out at 1400 lbs.
That boat had enough power to pull up 2 slalom skiers (numerous times :)
Admittedly, the seating was a bit sparse, but then I used it primarily
for fishing..
Mark
--
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
Mark Crafts :: mcr...@dale.ksc.nasa.gov
Harris Space Systems :: Melbourne, FL
Torsten Weirich
I'm thinking of buying a fairly small boat for skiing, fishing and
shoreline camping. The lake we generally camp on is fairly deep and there
are areas on shore where I can glide up right to the beach for disembarking. I
have to be careful when doing this because a few feet on either side of the
'safe' approach line are some submerged rocks. This isn't a real problem
when using our 15 foot aluminum boat and 15hp motor, but could be scary
with a fiberglass hull.
Well, if you hit a submerged rock hard enough to put a hole in a fiberglass
boat, the same scenario would probably also pop a few rivets and consequently
put a hole in your aluminum boat as well. I think if you're careful,
at most you'd end up scratching the gelcoat.
My real question is weight. My car has a towing capacity of about 2200
pounds and I'd always be towing the boat to the lake for the day.
There is a boat launch but no docking facilities on this lake. I'm
looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
appropriate trailer. The boat needs to be able to carry 3 people plus my
dog. Does anyone have an estimate of how much this setup would weigh
(minus the humans and dog)? If this is too much for my car to handle, I'll
have to re-think the type of boat I can get.
I'd recommend going to a larger aluminum boat. Two of my friends have
17' and 19' Smokercrafts...they're pretty nice boats and don't weigh
a whole lot.
Hope this helps.
Torsten Weirich
+---------------------------------------------------------------+
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+---------------------------------------------------------------+
000200 Lynch
stuff deleted
|>My real question is weight. My car has a towing capacity of about 2200
|>pounds and I'd always be towing the boat to the lake for the day.
|>There is a boat launch but no docking facilities on this lake. I'm
|>looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
|>appropriate trailer. The boat needs to be able to carry 3 people plus my
|>dog. Does anyone have an estimate of how much this setup would weigh
|>(minus the humans and dog)? If this is too much for my car to handle, I'll
|>have to re-think the type of boat I can get.
I suspect that for the boat you want your car might be marginal.
Here is something you can try to get a _ROUGH_ approximation of the
weight of the boat and trailer.
Weigh all of the equipment you are likely to put in your boat.
Add to that weight an estimate of the weight of a tank of gas.
Call this the load weight.
When you visit a prospective boat take your bathroom scales
along. Place the tongue jack of the trailer on the scales
with the trailer level. If the tongue weight plus 1/10th
of the load weight is greater than 220lb the boat/trailer
is too heavy for your car.
The tongue weight of a trailer is generally around 10% of
the total weight of the boat/trailer. This technique
probably won't work for a tandem trailer but that shouldn't
be a problem in your case.
The only way to be absolutly sure is to weigh the boat/trailer. Make
sure the boat has a full tank and all equipment you are likely to
put in it on a trip to the lake.
--
Hal Lynch
US Mail: Utah State University Internet: H...@cache.declab.usu.edu
Office of Computer Services Fax: (801)750-2268
Logan, Utah 84322-4410
David James Miller
|> The tongue weight of a trailer is generally around 10% of
|> the total weight of the boat/trailer. This technique
|> probably won't work for a tandem trailer but that shouldn't
The tongue weight SHOULD be around 10% of the total trailer weight. However,
this isn't always the case. Many trailers are set at 5% so the back end of
the car doesn't sag so much. Of course this adds to instability on the road
though.....
|>
|> The only way to be absolutly sure is to weigh the boat/trailer. Make
|> sure the boat has a full tank and all equipment you are likely to
|> put in it on a trip to the lake.
Good advice... but tough to do before purchasing, and then it's too late.
acss...@acs.eku.edu
> sure the boat has a full tank and all equipment you are likely to
> put in it on a trip to the lake.
> --
And make sure that you account for any people riding in the car and any
gear that you will have in the car. Weigh the car, boat and trailer to
check the combined gross weight.
As someone pointed out boat/trailer weights can be hard to guess. For
example I had an old Sea Ray 16'8" with a 6 cyl motor and on the single
axle trailer weighed 3700+ pounds (full tank/nogear). My new rig, 19'6"
350 V8 with tandom axle trailer weighs 3700+ pounds (full tank/nogear).
I would have guessed my old rig at around 3250 and I would have guessed
my new rig about right. The specs on my new boat were close. They listed
the boat at 2500# dry with a 4.3 engine. I figure 2650 dry with the V8
The trailer adds another ~1050 pounds. I think that is about as close as
you can ask them to get.
Dudley Cornman
acss...@acs.eku.edu
John F. Hughes
>In article <1993Sep15....@cc.usu.edu>, h...@kaos.declab.usu.edu (000200 Lynch) writes:
>|> The tongue weight of a trailer is generally around 10% of
>|> the total weight of the boat/trailer. This technique
>|> probably won't work for a tandem trailer but that shouldn't
>|> be a problem in your case.A
>
>The tongue weight SHOULD be around 10% of the total trailer weight. However,
>this isn't always the case. Many trailers are set at 5% so the back end of
>the car doesn't sag so much. Of course this adds to instability on the road
>though.....
OK, it's finally time to ask the question. I've heard the "10% tongue weight"
advice for years, and have doggedly followed it (although my iceboat
trailer's probably nearer the 15% mark), but I've always wondered "Why?"
Can some bright soulout there enlighten me? Clearly if the tongue weight
were negative I could see some problems (like my rear tires being lifted
off the pavement :-( ), and if it's too big, in absolute terms, then
my front wheels start running light on the pavement, and with fast acceleration
I'll pop a wheelie, so to speak. But I'm not at all clear on why 10%
is such a magic number...
-John
--
______________________________________________________________________________
John F. Hughes | I was in this prematurely airconditioned supermarket,
j...@cs.brown.edu | and there were all these ... aisles.
...!brunix!jfh | -Lucinda Childs
David James Miller
|> In article <279ksg$4...@meaddata.meaddata.com> dav...@meaddata.com (David James Miller) writes:
|> >In article <1993Sep15....@cc.usu.edu>, h...@kaos.declab.usu.edu (000200 Lynch) writes:
|> >|> The tongue weight of a trailer is generally around 10% of
|> >|> the total weight of the boat/trailer. This technique
|> >|> probably won't work for a tandem trailer but that shouldn't
|> >|> be a problem in your case.A
|> >
|> >The tongue weight SHOULD be around 10% of the total trailer weight. However,
|> >this isn't always the case. Many trailers are set at 5% so the back end of
|> >the car doesn't sag so much. Of course this adds to instability on the road
|> >though.....
|>
|> OK, it's finally time to ask the question. I've heard the "10% tongue weight"
|> advice for years, and have doggedly followed it (although my iceboat
|> trailer's probably nearer the 15% mark), but I've always wondered "Why?"
|>
|> Can some bright soulout there enlighten me? Clearly if the tongue weight
|> were negative I could see some problems (like my rear tires being lifted
|> off the pavement :-( ), and if it's too big, in absolute terms, then
|> my front wheels start running light on the pavement, and with fast acceleration
|> I'll pop a wheelie, so to speak. But I'm not at all clear on why 10%
|> is such a magic number...
|>
I think 10% is actually considered the minimum safe weight to prevent
excessive swaying. I think more is better, provided the tow vehicle can
handle it. I've read some articles about it in Trailerboats - I'll see
if I can dig them out tonight.
Robert Hanners
>Can some bright soulout there enlighten me? Clearly if the tongue weight
>were negative I could see some problems (like my rear tires being lifted
>off the pavement :-( ), and if it's too big, in absolute terms, then
>my front wheels start running light on the pavement, and with fast acceleration
>I'll pop a wheelie, so to speak. But I'm not at all clear on why 10%
>is such a magic number...
John, I've meant to do the analysis on this for years, but never found
a convenient time while it was still on my mind. So this is just
speculation tempered with some experience. I'm sure you know that the
10% recommendation is not for either of the above (though they could
pose a bit of trouble :-) ), but rather to prevent the auto and trailer
from going into dynamic instability (uncontrolled sway) at higher speeds.
In order to really understand the problem, one has to look at the dynamic
equations involving the auto and trailer mass centers-of-gravity, their
moments-of-inertia, the relative tire and hitch locations, the suspension
spring-rates, and the (very non-linear) tire angle-to-lateral force/
velocity profile. A relatively simple problem with today's computers,
but quite difficult before at least the arrival of analog computers.
Anyway, it is apparent that a positive feedback occurs with too light
of a tonque "weight", where a side sway (and rotation) of the trailer
feeds back a force at the hitch which throws the car into an attitude
that reinforces the trailer sway. The process repeats in a resonant
manner which in extreme cases can cause the vehicle tires to break free
and jack-knife. Generally there is enough frictional dissipation in
the lateral tire scrub to prevent disaster. Scrubbing usually provides
enough damping to allow recovery (by slowing) before the periodic
deflections build to bad day proportions.
Insofar as why 10%, I can't say without pushing the numbers, but I suspect
its due primarily to that being a good balance between too much weight on
the car hitch causing the car to be unstable (the automobile equivalent
of tail heavy aircraft) and too little weight causing the mentioned
trailer positive feedback effect. I believe the feedback is positive
when the trailer tires are in front of the trailer center-of-percussion
for trailer rotation about the hitch.
Taking this a bit further, visualize the trailer as a baseball bat.
When you hit the ball outside the "sweet spot" (center-of-percussion),
the bat is kicked *forward* in your hands. Hit the ball on the sweet
spot and there's virtually no kick or sting at the hands. Now, hit
the ball inside the sweet spot; the bat is kicked backward. This last
situation is analagous to unstable positive feedback condition caused
by the trailer tires being too far forward relative to the trailer
center-of-gravity.
We could go on, but too much speculation without some number crunching
could prove embarrassing for someone who supposedly is in the dynamics
arena. :-) Besides everyone including purhaps you, John, have hit "n"
already anyhow. :-)
-- Bob
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Robert J. Hanners Carderock Division
han...@oasys.dt.navy.mil Naval Surface Warfare Center
-the dry dB game- Annapolis, Maryland
acss...@acs.eku.edu
>
> Can some bright soulout there enlighten me? Clearly if the tongue weight
> were negative I could see some problems (like my rear tires being lifted
> off the pavement :-( ), and if it's too big, in absolute terms, then
Long before your tires are lifted of the pavement light tounge weight
will cause your trailer to sway at highway speeds. Unless your tow
vehicle greatly outweighs your boat... you will want to wake up Henry...
cause Henry's never seen a wreck like your'ea fixin ta have.
Heavy tounge weight is most likely to cause the toung of the trailer to
"bounce" the rear of the vehicle which reduces the front tires ability
to maintain directional control. Generally, I would guess that a bit
heavy is FAR safer that a bit light undermost circumstances.
I don't know exactly why you hear so much about 10% and 15%, except that
it works. I am sure there are some physics and impressive math behind it
somewhere though. Generally, 10% +\- is recommended for single axles,
15% +\- for tandoms. If the trailer is equal or greater to the weight of
the tow vehicle and/or if the tow vehicle is very short and the trailer
long, tounge weight can be very critical and there may be less room for
error. Multiple axle setups tend to be more forgiving than singles.
There are sway control devices that you can buy if for some reason you
just can't get it balanced right.
Does anybody know if this pattern continues for triples and quads?
Dudley Cornman
acss...@acs.eku.edu
Rod Mc Innis
>In rec.boats, j...@cs.brown.edu (John F. Hughes) writes:
>
>>Can some bright soulout there enlighten me? Clearly if the tongue weight
>>were negative I could see some problems (like my rear tires being lifted
>>off the pavement :-( ), and if it's too big, in absolute terms, then
>>my front wheels start running light on the pavement, and with fast acceleration
>>I'll pop a wheelie, so to speak. But I'm not at all clear on why 10%
>>is such a magic number...
>
>Insofar as why 10%, I can't say without pushing the numbers, but I suspect
>its due primarily to that being a good balance between too much weight on
>the car hitch causing the car to be unstable (the automobile equivalent
>of tail heavy aircraft) and too little weight causing the mentioned
>trailer positive feedback effect. I believe the feedback is positive
>when the trailer tires are in front of the trailer center-of-percussion
>for trailer rotation about the hitch.
>
It seems to me that there are two issues getting confused. Tongue weight does not have a direct
relation to trailer sway, except that how the boat is sitting on the trailer will deteremin both.
Roberts post refers to the trailer springs, cars springs, tires, and a lot of other factors that
determine the characteristics of the combined vehicles. This is all very true, but tongue wieght is
very simple, it is the ratio of where the center of mass is in relation to the center of axel (I Know
this is not the proper term, but I *don't know the proper term for center of rotation when dual axels
are in use).
Take the case of a trailer (not a boat, just a simple box trailer) loaded with a 500 pound weight.
You put this weight directly over the trailers wheels, and you could have little or no tongue weight,
yet it will pull very nicely. Move it forward a foot, and you have positive tongue, move it back, and
negative tongue weight.
Now take the same trailer with two 250 pound weights, one in the front, one in the back. If they
are both the same distance from the axel, there will be no tongue weight. However, the trailer will
*not* tow well, due to the moment of inertia the mass has over the trailer wheels/springs.
Furthermore, adding weight to the front (to give tongue weight) will not help.
It is very easy to make the false connection between tongue weight and towing well simply because
people with stern engine boats (outboards, I/Os) may notice it tows better when the boat is loaded
farther forward. But it is not because you have more tongue weight, it is because you go the mass
(the engine) closer to the trailer wheels. It just so happens that you added tongue weight at the
same time.
Rod
Jeff Huntington
> In article <279ssu$d...@cat.cis.Brown.EDU>, j...@cs.brown.edu (John F. Hughes) writes:
> >
> Multiple axle setups tend to be more forgiving than singles.
This sure has not been my experience. Single axle trailers seem to be fairly
forgiving in that they seem to have a wider range of tongue weight where nothing
too bad happens. Sure, the trailer will sway a little. But, get the load
too light on the tongue of a tandem trailer, and look out! The front and rear
wheels work together to steer the trailer all over the road - with authority!
Jeff Huntington
Dave Kinzer
>
>OK, it's finally time to ask the question. I've heard the "10% tongue weight"
>advice for years, and have doggedly followed it (although my iceboat
>trailer's probably nearer the 15% mark), but I've always wondered "Why?"
I think it is an easy way to check that the center of mass is sufficently
in front of the point that lateral force will be applied by the wheels.
This is important for preventing oscillations from occuring.
Imagine a back weighted trailer traveling straight down a road.
A small irregularity causes the trailer to shift slightly to one side.
The tire direction now causes a force be applied to the load to get it
back in line with the car. The force, being in front of the center of
mass, causes the trailer tongue to be forced even more out of line
(assuming your car is not of infinate mass, and has suspension) with
the direction of travel, further increasing the force (positive feedback.)
Depending on speed and the characteristics of the car and trailer,
the trailer can overshoot the in-line position, causing the cycle
to repeat on the other side. If severe enough it can cause a loss of
control.
-dave
Robert Hanners
>I don't know exactly why you hear so much about 10% and 15%, except that
>it works. I am sure there are some physics and impressive math behind it
>somewhere though. Generally, 10% +\- is recommended for single axles,
>15% +\- for tandoms.
This surprises me as it has been my (limited) experience that I could
get away with proportionately *less* trailer weight on the tongue for
a tandem. Less also seems consistant with your comment highlighted
below, with which I agree. This is attributed to the inherient resistance
of a tandem to lateral rotation; that is, rotation causes greater tire
scrubbing losses that damp the system.
>If the trailer is equal or greater to the weight of
>the tow vehicle and/or if the tow vehicle is very short and the trailer
>long, tounge weight can be very critical and there may be less room for
>error. Multiple axle setups tend to be more forgiving than singles.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>There are sway control devices that you can buy if for some reason you
>just can't get it balanced right.
These too induce frictional energy dissipation to damp the system.
They're remarkably effective-- worked like a charm for me. The types
that employ load leveler bars also more evenly load the towing vehicle,
placing more weight on the front tires. With them, I towed my 26 foot
ketch, which with the trailer and camping gear totalled 8500 lb, over
20,000 miles with no problem.
>Does anybody know if this pattern continues for triples and quads?
I would doubt that there would be a noticeable improvement over twin
tandem axles-- unless the wheel base really gets spectacular-- mainly
because triples and quads are generally applied to proportionately
longer trailers.
Robert Hanners
I agree with your explanation using the two 250 lb weight illustration
up to a point. But you've fallen into a trap which I'll describe in
a moment.
First though, I believe that you've done me a disservice. You speak
of my reference to "... springs, tires, and a lot of other factors",
then suggest that I'm missing the point and go into a discussion of
the importance of the mass moment-of-inertia. Well, if you review my
post, you will find that among those "a lot of other factors", I
specifically listed mass moments-of-inertia. I then went on (and on)
:-) to speak primarily of the center-of-percussion which is a function
directly of mass, the mass location relative to the rotation axis, and
(!) the *mass moment-of-inertia*. The center-of-percussion in fact
is simply the engineer's term for a value that helps quantify the
effects that you were discussing.
Now the trap. You mention that the handling of the two 250 lb mass
trailer can't be improved by adding weight to the front. Generally
speaking you're correct, precisely in fact if you're suggesting adding
the weight directly over the hitch. *But*, that is not how the boat
owner typically goes about establishing tongue weight. Usually the
first move is to adjust the position of the entire boat on the trailer
by moving the bow chock. This is *not* equivalent to simply adding
weight at the front on the trailer.
Again your point is well taken that tongue weight is not the only factor
to be considered and I was certainly not suggesting that it was. As
a practical matter however many people don't have an appreciation of
what mass m-o-i is, let alone what to do with it. The 10% tongue weight
criterion is a reasonably good measure for most trailers however and
is a value that can be often measured with but a bathroom scales.
Generally m-o-i can only be reduced modestly to reduce swaying while
trailering. Small outboards can be removed from the transom and, together
with anchors and fuel tanks, placed in the center of the boat. That's
about it. You're stuck with it. All that's left is moving the boat
forward (or, on some trailers, moving the axle aft).
acss...@acs.eku.edu
> Take the case of a trailer (not a boat, just a simple box trailer) loaded with a 500 pound weight.
> You put this weight directly over the trailers wheels, and you could have little or no tongue weight,
> yet it will pull very nicely. Move it forward a foot, and you have positive tongue, move it back, and
> negative tongue weight.
>
> Now take the same trailer with two 250 pound weights, one in the front, one in the back. If they
> are both the same distance from the axel, there will be no tongue weight. However, the trailer will
> *not* tow well, due to the moment of inertia the mass has over the trailer wheels/springs.
> Furthermore, adding weight to the front (to give tongue weight) will not help.
I think the reason it will tow very well is because the tow vehicle will
greatly out weigh it and is in total control. If you tried this same test,
but used a tow vehicle that only weighed 300 pounds and gould get up to
55 or 60 mph, I think you'd have your hands full.
I even have a friend that tows about 2200-2500 pounds of boat and
trailer (single axle) behind a older Suburban. Even though the Burb
outweighs the boat and trailer (probably over 2:1) it becomes
slightly unstable at speeds above 70-75 mph. At legal speeds, it's fine.
his tounge weight is probably only 75 pounds.
dsc
acss...@acs.eku.edu
I guess I was reffering to the sway and the beating the tounge of my old
trailer used to dish out. I should also say that it was an old Shore
Station, half roller piece of shit.
My guess is singles are more forgiving on the lighter side and tamdoms
are more forgiving on the heavy side?
dsc
Rick Haslip
Hey! Who hijacked my thread? :) You know, my rookie boat weight question?
Now I'm reading about moments of inertia(?) and all kinds of wierd
physics stuff. Little did I know.
Nah, just kidding. It's great. The more I read, the more I need to know. I
think I'm getting a headache and had better go lay down for a rest.
Physics has always had that effect on me.
However, I sure am learning a heck of a lot of valuable stuff here, stuff
I hadn't really even thought about before.
Thanks for all the insight and information. Keep it coming. (NO sarcasm
intended!)
Rick Haslip
Robert Hanners
>Hey! Who hijacked my thread? :) You know, my rookie boat weight question?
>Now I'm reading about moments of inertia(?) and all kinds of wierd
>physics stuff. Little did I know.
Sorry, Rick. Here's your thread back-- a bit worn, but still serviceable.
Thanks for the loan. Beats coming up with a subject on a rainy day.
>Nah, just kidding. It's great. The more I read, the more I need to know. I
>think I'm getting a headache and had better go lay down for a rest.
>Physics has always had that effect on me.
Physics always affect me as advertised.
>However, I sure am learning a heck of a lot of valuable stuff here, stuff
>I hadn't really even thought about before.
>Thanks for all the insight and information. Keep it coming. (NO sarcasm
>intended!)
Careful, you're risking your posting priviledges talking like that.
Your admin already has 50 messages of outrage over this excess.
Rod Mc Innis
>First though, I believe that you've done me a disservice. You speak
>of my reference to "... springs, tires, and a lot of other factors",
>then suggest that I'm missing the point and go into a discussion of
>the importance of the mass moment-of-inertia. Well, if you review my
>post, you will find that among those "a lot of other factors", I
>specifically listed mass moments-of-inertia. I then went on (and on)
>:-) to speak primarily of the center-of-percussion which is a function
>directly of mass, the mass location relative to the rotation axis, and
>(!) the *mass moment-of-inertia*. The center-of-percussion in fact
>is simply the engineer's term for a value that helps quantify the
>effects that you were discussing.
I apologize if you were offended by my attempt to shortcut. I thought very
highly of your discussion of m-o-i, and identifying the factors that are
involved. My reference to 'a lot of other factors' was intended to give you
credit without repeating all of them.
>
>Now the trap. You mention that the handling of the two 250 lb mass
>trailer can't be improved by adding weight to the front. Generally
>speaking you're correct, precisely in fact if you're suggesting adding
>the weight directly over the hitch. *But*, that is not how the boat
>owner typically goes about establishing tongue weight. Usually the
>first move is to adjust the position of the entire boat on the trailer
>by moving the bow chock. This is *not* equivalent to simply adding
>weight at the front on the trailer.
I agree. Did you read my last two paragraphs? Another trap is the boat
owner moving mass (such as a gas tank) from the stern to the bow. He may
increase tongue weight, but he would have been better off to put the weight
over the trailer wheels.
>
>Again your point is well taken that tongue weight is not the only factor
>to be considered and I was certainly not suggesting that it was. As
>a practical matter however many people don't have an appreciation of
>what mass m-o-i is, let alone what to do with it. The 10% tongue weight
>criterion is a reasonably good measure for most trailers however and
>is a value that can be often measured with but a bathroom scales.
>Generally m-o-i can only be reduced modestly to reduce swaying while
>trailering. Small outboards can be removed from the transom and, together
>with anchors and fuel tanks, placed in the center of the boat. That's
>about it. You're stuck with it. All that's left is moving the boat
>forward (or, on some trailers, moving the axle aft).
>
>-- Bob
>
I think that you miss my point. tongue weight is *not* a measure of how
well the trailer will tow. Tongue weight is *not* a factor at all. Saying
that you need 10% tongue weight in order to have a stable rig is absurd. A
trailer can have zero tongue weight and tow well, or 50% and still tow bad.
What you do need tongue weight for is to keep the hitch riding on the ball
instead of riding on the keeper (the latch that keeps the trialer from jumping
off.) Without adequate tongue weight, the hitch will attempt to bounce off on
every dip and bump in the road. In addition to being noisy, it could be
dangerous if the keeper were to fail or work loose.
I am actually amused by some of the other posts that attempt to make the
blanket statements about forces acting as positive feedback, without any
mention of damping factors, phase, frequency, etc. I know enough about it to
know that I could never calculate ahead of time what a rig would do. Hell, in
my servo systems I figure that I am doing good when I get initial values close
enough to get a bodi plot.
Rod
Greg Pavlov
>
> Well, if you hit a submerged rock hard enough to put a hole in a fiberglass
> boat, the same scenario would probably also pop a few rivets and consequently
> put a hole in your aluminum boat as well. I think if you're careful,
> at most you'd end up scratching the gelcoat.
>
greg pavlov
pav...@fstrf.org
Greg Pavlov
> advice for years, and have doggedly followed it (although my iceboat
> trailer's probably nearer the 15% mark), but I've always wondered "Why?"
>
pulling a few trailers and from fiddling around with a weight distribution
hitch, the problem with too little relative weight on the car is that I
seem to lose much of the directional control I should have over the trailer.
It tends to "sway" and wander back and forth behind me.
If you are towing a heavy boat (heavy relative to your tow vehicle's weight),
by the way, I strongly recommend using a weight distribution hitch. It's
definitely increased my "comfort level" while towing.
greg pavlov
pav...@fstrf.org
Greg Pavlov
> In article <CDCML...@freenet.carleton.ca> ad...@Freenet.carleton.ca (Rick Haslip) writes:
> >
> >... There are areas on shore where I can glide up right to the beach for
> > disembarking. I have to be careful when doing this because a few feet on
> > either side of the 'safe' approach line are some submerged rocks. This
> > isn't a real problem when using our 15 foot aluminum boat and 15hp motor,
> > but could be scary with a fiberglass hull.
> >
> >My real question is weight. My car has a towing capacity of about 2200
> >I'm looking at a 16 to 17 foot bowrider with 100-150 hp outboard and the
> >appropriate trailer. The boat needs to be able to carry 3 people plus my
> >dog.
You may want to look at larger aluminum boats. I sense that you are not
only looking for a larger boats, but one that is layed out along the lines
of the "typical" fiberglass bowrider. There are decent aluminum versions of
same.
For example: Crestliner has a 17'6" model (called the "V170 Sportfish").
With a V6 i/o, it weighs 1280 lbs; I assume that the same boat with an
equivalent power outboard, will weigh apx. 900 - 950 lbs. Assume 150 lbs
for fuel, 200 lbs for the usual boat junk, and 500 - 600 (?) lbs for a
trailer. This leaves you within your limit (I tried to be conservative).
The above has an official weight capacity of 1400 lbs, by the way; I believe
that this includes the engine.
greg pavlov
pav...@fstrf.org
Torsten Weirich
You really think so? I'd say the average hole in my fiberglass would cost
about $150-$175 to fix. Do you have a similar figure for say a 3-4" diameter
hole?
acss...@acs.eku.edu
> In article <31...@niktow.canisius.edu> pav...@niktow.canisius.edu (Greg Pavlov) writes:
>
> In article <61...@unisql.UUCP>, tor...@unisql.UUCP (Torsten Weirich) writes:
> >
> > Well, if you hit a submerged rock hard enough to put a hole in a fiberglass
> > boat, the same scenario would probably also pop a few rivets and consequently
> > put a hole in your aluminum boat as well. I think if you're careful,
> > at most you'd end up scratching the gelcoat.
> >
> But the aluminum boat would cost considerably less to fix....
>
> You really think so? I'd say the average hole in my fiberglass would cost
> about $150-$175 to fix. Do you have a similar figure for say a 3-4" diameter
> hole?
>
Wouldn't you thing an impact that made a 3-4" hole in fiberglass would
make a 3-4" dent in aluminium and a 1" or smaller hole, which could
easily be repaired with marine epoxy. And what is causing you to come in
to the beach hard enough to put a hole or dent in either. That is what
he was asking about in the first place wasn't it, landing on a narrow
patch of beach between some large rocks. Personally, I would prefer
an unpainted aluminium hull for this asn I realy wouldn't care if I
scratched or dented aluminium, but I'd hate to treat fiberglass that
way.
As for the case of a larger hole in aluminium, if I could find ordinary
aluminium welding materials (not marine alloys, I don't go to salt water
anyway) that were compatabile, I cold get it fixed pretty cheap. True,
it might not last as long, especially if I continue to visit that rock
guarded beach, but that's life.
If you do choose to do it right and use the marine materials and get it
done at a marine repair shop... plan to get soaked, just like always.
For instance, I broke the skeg off my first boat moving it around in
winter storage (the battery was unhooked and the drive as down and I
normally had 3-4" clearance in this mode.. backed into a 5" hump).
One of the local dealers has a man that comes around every so often and
fixes everything aluminium. He wanted $150-$200 to fix it. A local
one-man machine shop fixed it for $25, that was 3 years ago, it's still
there doing its job, no problems.
dsc
Bob Rusk
>As for the case of a larger hole in aluminium, if I could find ordinary
>aluminium welding materials (not marine alloys, I don't go to salt water
>anyway) that were compatabile, I cold get it fixed pretty cheap. True,
>it might not last as long, especially if I continue to visit that rock
>guarded beach, but that's life.
>
>If you do choose to do it right and use the marine materials and get it
>done at a marine repair shop... plan to get soaked, just like always.
My neighbors at the lake where we had a cottage when I was a kid had an _old_
Starcraft rowboat that had been to hell and back. Whenever they holed it,
they would rivet on a patch of marine aluminum. Not a terribly difficult
thing to do, by the looks of it.
--
Bob Rusk
rr...@ssd.csd.harris.com
My thoughts, probably not Harris'.