Boat Topic: Coefficient of Friction & Pulling Boat onto Trailer
 

Background then Question:

We have a problem where our trailered boat does not set properly on the
trailer. When we pull it onto the trailer the bow is touching the bow-stop
on the trailer. But as we pull the boat & trailer up the ramps the bow post
moves a bit away from the boat so that the boat's bow ends up 2" or 3" from
the trailers bow-post.

This is ok for short distances but when we trailer longer distances, the rig
rides much better if the boat is touching the trailer at the bow-post.

On most boat there is, of course, a bow-eye and you just pull the boat
forward with a winch. But this boat is an older wooden boat. It does not
have a bow-eye and we can not install one -- it would just pull the bow out
of the boat.

The boat *does* have lifting rings at the bow & stern. These were meant for
a straght up lifting of the boat. This is how the boat is supposed to be put
into the water.

We can put some pull on this lifting ring. And, possibly, we can reinforce
it so we can put more pull on it.

So...my QUESTION:

The boat weight about 4000 lbs. I've done a little googeling and read about
coefficient of friction.

#1: Am I right in thinking the Coefficient of Friction can not be more than
1.0
In other words, the MAX force needed to pull the boat forward is 4000
lbs.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter as
far as
increasing or decreasing the friction?

Gary wrote:
Background then Question:

We have a problem where our trailered boat does not set properly on the
trailer.

You need a set of bunks conformed to the hull shape.


On most boat there is, of course, a bow-eye and you just pull the boat
forward with a winch. But this boat is an older wooden boat. It does not
have a bow-eye and we can not install one -- it would just pull the bow out
of the boat.

I hope that's not true, if so your boat is seriously underbuilt. A
wooden boat will have stem & keel members, they should be strong enough
to lift the boat much less pull it onto a trailer.

It would be worth your while to install a bow eye, and if it needs some
backup structural work, so be it.


So...my QUESTION:

The boat weight about 4000 lbs. I've done a little googeling and read about
coefficient of friction.

#1: Am I right in thinking the Coefficient of Friction can not be more than
1.0
In other words, the MAX force needed to pull the boat forward is 4000
lbs.


No. Max CFr can be far greater than 1, in theory it can reach infinity.
In normal circumstances, sliding friction ranges from about .2 to .7 but
it can be reduced with substances called "lubricants" and increased with
substances called "glue." Dazzling new technology ;)


#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter as
far as
increasing or decreasing the friction?


That's pretty much correct, for most surfaces the decrease in load
bearing matches the increase in friction due to surface area.

My suggestions- check the weight distribution on the bunks, try to get
more of the weight onto the trailer rollers... try changing the carpet
surface... add a set of transverse bunks conformed to the hull shape...
use slippery bottom paint...

Fair Skies
Doug King

On Tue, 15 Mar 2005 14:56:12 -0500, "Gary"
wrote:

~~ snippage ~~

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding that the amount of surface area between the boat &
bunks does not matter as far as ncreasing or decreasing the friction?

The wider the surface, the more surface area for grip and vice versa.

However, other factors can reduce grip such as paint, wax, angle of
the trailer, etc.

On my Ranger, I wax the bunks which assists getting the boat on and
off the trailer when single handing the boat.

If you have four lifting points, why not use tow straps and use the
winch to pull the boat forward until it's sound against the bow stop?

Or get a crane for a tow vehicle. :)

Later,

Tom

Doug,

Thanks for taking the time.


You need a set of bunks conformed to the hull shape.

Actually, the bunks are formed to the hull quite well. We bolted the
supports on in-place with the boat already setting above the trailer
(on blocks). So they fit darn near perfecty.



I hope that's not true, if so your boat is seriously underbuilt. A wooden
boat will have stem & keel members, they should be strong enough to lift
the boat much less pull it onto a trailer.


The keel is plenty strong (huge timber). But figuring that the boat weighs
4000 lbs the force to pull on it might be up to, what?, 2000 or more
lbs. And the stem is a seperate part from the keel. I don't know as that
I'd want to be pulling the boat by that. It was built to take pressure
*pushing*
on the keel. But it was never built for the keel to be pulled on.
(Remember,
this boat was built to be LIFTED by the lift rings.)






#1: Am I right in thinking the Coefficient of Friction can not be more
than 1.0


No. Max CFr can be far greater than 1, in theory it can reach infinity. In
normal circumstances, sliding friction ranges from about .2 to .7

Ok, thanks.


but it can be reduced with substances called "lubricants" and increased
with substances called "glue." Dazzling new technology ;)


Wise a**.




My suggestions- check the weight distribution on the bunks, try to get
more of the weight onto the trailer rollers... try changing the carpet
surface... add a set of transverse bunks conformed to the hull shape...
use slippery bottom paint...


The only roller is the keel roller. the rest of the boat is supported on
bunks
and that's what we're supposed to do with wood boat. Not very possible
to shift any more weight to the keel.

I agree about changing the carpet surface to something like high-density
plastic
that might be more slippery. Also might try that new fangeled "lubricant"
stuff
they make to spray on the carpet.



Fair Skies
Doug King

May the Four Winds Blow You Safely Home,
Gary

"Short Wave Sportfishing" wrote in message


The wider the surface, the more surface area for grip and vice versa.


But the wider the surface the less weight is on each square inch...so my
understanding
is the overall friction is the same. But I'm not sure.



If you have four lifting points, why not use tow straps and use the
winch to pull the boat forward until it's sound against the bow stop?

Nope, just two lifting points. Pulling from the stern one is not practicle
cause the windsheld is between. We can pull a bit on the bow lifting
ring, but it's really made for...uh...lifting. I don't think it should be
pulled
with more than a few hundred pounds pressure.



Or get a crane for a tow vehicle. :)


Hmmmmmm..........


Later,

Tom

Thanks for the ideas, Tom.

Gary

Gary wrote:

"Short Wave Sportfishing" wrote in message

The wider the surface, the more surface area for grip and vice versa.



But the wider the surface the less weight is on each square inch...so my
understanding
is the overall friction is the same. But I'm not sure.



If you have four lifting points, why not use tow straps and use the
winch to pull the boat forward until it's sound against the bow stop?


Nope, just two lifting points. Pulling from the stern one is not practicle
cause the windsheld is between. We can pull a bit on the bow lifting
ring, but it's really made for...uh...lifting. I don't think it should be
pulled
with more than a few hundred pounds pressure.



Or get a crane for a tow vehicle. :)



Hmmmmmm..........



Later,

Tom


Thanks for the ideas, Tom.

Gary


Put in a bow eye, with a cable run to the transom, to share the load.
You can remove or install it at will

On Tue, 15 Mar 2005 17:09:24 -0500, "Gary"
wrote:


"Short Wave Sportfishing" wrote in message


The wider the surface, the more surface area for grip and vice versa.

But the wider the surface the less weight is on each square inch...so my
understanding is the overall friction is the same. But I'm not sure.

That is true, but less pressure per square inch is compensated for by
the area. What has more friction - 4k psi on a half inch square or 4k
psi on ten square feet? The answer is it depends.

The problem with figuring friction is that there are any number of
variables which enter into any mathematical construct for existing
materials. To develop the COF, you have to develop two points - the
breaking force (described as the weight, acceleration or energy
required to make one material slide against another) and the sustained
force (that which allows one material to continue to slide against
another).

You could certainly develop the COF from some simple experiments, but
I'm afraid you might damage your boat. :)

I think what you are really looking for is how to configure the bunks
such that the boat is properly supported and how to keep it from
moving which, admittedly, has something to do with friction, it really
has more to do with configuration.

You could so something that I saw once and that's make the front of
the bunks lower that the rear of the bunks - that way the weight is
forward and with proper application of wax, it would probably stay
that way.

Later,

Tom

Gary wrote:
Doug,

Thanks for taking the time.


You're quite welcome.



You need a set of bunks conformed to the hull shape.


Actually, the bunks are formed to the hull quite well. We bolted the
supports on in-place with the boat already setting above the trailer
(on blocks). So they fit darn near perfecty.


My preference is 2 or 3 transverse bunk matched to the boat's hull
section, aligned with the bulkheads inside the hull. Best support you
can have out of the water, and it puts the boat in exactly the right
spot on the trailer every time.



The keel is plenty strong (huge timber). But figuring that the boat weighs
4000 lbs the force to pull on it might be up to, what?, 2000 or more
lbs. And the stem is a seperate part from the keel. I don't know as that
I'd want to be pulling the boat by that. It was built to take pressure
*pushing*
on the keel. But it was never built for the keel to be pulled on.
(Remember,
this boat was built to be LIFTED by the lift rings.)


Well, think about how much force it takes to push it through the water
at full speed. All that force is transmitted through the keel & frames
(probably floor timbers) & planks.


but it can be reduced with substances called "lubricants" and increased
with substances called "glue." Dazzling new technology ;)



Wise a**.

Sorry, couldn't resist





My suggestions- check the weight distribution on the bunks, try to get
more of the weight onto the trailer rollers... try changing the carpet
surface... add a set of transverse bunks conformed to the hull shape...
use slippery bottom paint...



The only roller is the keel roller. the rest of the boat is supported on
bunks
and that's what we're supposed to do with wood boat.

Yep, that's true


I agree about changing the carpet surface to something like high-density
plastic
that might be more slippery.

I used free... picked up by the side of the road... heavy shag carpet on
a number of trailers but it is not really good for it. Most recently
I've been using a fairly high grade of rubber backed indoor-outdoor
loop-pile carpet.


... Also might try that new fangeled "lubricant"
stuff
they make to spray on the carpet.


Hmm, you might be careful asking for "carpet lubricant" at Home Depot!
But waxing the hull... or even putting on this Teflon stuff they make
for trailerable racing sailboats... Starbrite is one brand of it...

Fair Skies
Doug King

Move the post 2" to 3" forward ... the boat'll end up exactly where you want
it :-)

"Gary" wrote in message
...

Background then Question:

We have a problem where our trailered boat does not set properly on the
trailer. When we pull it onto the trailer the bow is touching the bow-stop
on the trailer. But as we pull the boat & trailer up the ramps the bow
post
moves a bit away from the boat so that the boat's bow ends up 2" or 3"
from
the trailers bow-post.

This is ok for short distances but when we trailer longer distances, the
rig
rides much better if the boat is touching the trailer at the bow-post.

On most boat there is, of course, a bow-eye and you just pull the boat
forward with a winch. But this boat is an older wooden boat. It does not
have a bow-eye and we can not install one -- it would just pull the bow
out
of the boat.

The boat *does* have lifting rings at the bow & stern. These were meant
for
a straght up lifting of the boat. This is how the boat is supposed to be
put
into the water.

We can put some pull on this lifting ring. And, possibly, we can reinforce
it so we can put more pull on it.

So...my QUESTION:

The boat weight about 4000 lbs. I've done a little googeling and read
about
coefficient of friction.

#1: Am I right in thinking the Coefficient of Friction can not be more
than
1.0
In other words, the MAX force needed to pull the boat forward is 4000
lbs.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter
as
far as
increasing or decreasing the friction?

Okokok ... assuming the problem is that the boat is sliding backwards as you
drive/bounce your way up the ramp, you don't need to pull the boat forward
when you get to the top of the ramp ... you just need to secure it to the
trailer (to the bow-post seems most reasonable) before you start up the ramp
(that's basically what I do when I power even my little the boat onto the
trailer). Maybe you've got a cleat or two up front that could be used to do
the job?

"bowgus" wrote in message
...
Move the post 2" to 3" forward ... the boat'll end up exactly where you
want
it :-)

"Gary" wrote in message
...

Background then Question:

We have a problem where our trailered boat does not set properly on the
trailer. When we pull it onto the trailer the bow is touching the
bow-stop
on the trailer. But as we pull the boat & trailer up the ramps the bow
post
moves a bit away from the boat so that the boat's bow ends up 2" or 3"
from
the trailers bow-post.

This is ok for short distances but when we trailer longer distances, the
rig
rides much better if the boat is touching the trailer at the bow-post.

On most boat there is, of course, a bow-eye and you just pull the boat
forward with a winch. But this boat is an older wooden boat. It does not
have a bow-eye and we can not install one -- it would just pull the bow
out
of the boat.

The boat *does* have lifting rings at the bow & stern. These were meant
for
a straght up lifting of the boat. This is how the boat is supposed to be
put
into the water.

We can put some pull on this lifting ring. And, possibly, we can
reinforce
it so we can put more pull on it.

So...my QUESTION:

The boat weight about 4000 lbs. I've done a little googeling and read
about
coefficient of friction.

#1: Am I right in thinking the Coefficient of Friction can not be more
than
1.0
In other words, the MAX force needed to pull the boat forward is
4000
lbs.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter
as
far as
increasing or decreasing the friction?

The friction thing has been answered.
As for the bow problem. Issue is that as the rear of the boat sets down on
the trailer the bow lifts and moves away from the bow stop. Normally this
is solved w/ the wench and bow eye which holds the boat tight to the bow as
the rear goes down pulling the boat forward.

I can understand your desire to not install an eye.
Your best option would be to setup the trailer so you can adjust the bow
stop easily. Set the boat tight to the stop. Pull the boat out. Adjust
bow stop tight to the boat. This can be done any number of ways from
sliding the entire bow stop on the trailer to just adjusting the roller on
the stop. Should be able to come up w/ a sliding mechanism fairly easily.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"Gary" wrote in message
...

Background then Question:

We have a problem where our trailered boat does not set properly on the
trailer. When we pull it onto the trailer the bow is touching the bow-stop
on the trailer. But as we pull the boat & trailer up the ramps the bow
post moves a bit away from the boat so that the boat's bow ends up 2" or
3" from the trailers bow-post.

This is ok for short distances but when we trailer longer distances, the
rig rides much better if the boat is touching the trailer at the bow-post.

On most boat there is, of course, a bow-eye and you just pull the boat
forward with a winch. But this boat is an older wooden boat. It does not
have a bow-eye and we can not install one -- it would just pull the bow
out of the boat.

The boat *does* have lifting rings at the bow & stern. These were meant
for a straght up lifting of the boat. This is how the boat is supposed to
be put into the water.

We can put some pull on this lifting ring. And, possibly, we can reinforce
it so we can put more pull on it.

So...my QUESTION:

The boat weight about 4000 lbs. I've done a little googeling and read
about coefficient of friction.

#1: Am I right in thinking the Coefficient of Friction can not be more
than 1.0
In other words, the MAX force needed to pull the boat forward is 4000
lbs.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter
as far as
increasing or decreasing the friction?

On Wed, 16 Mar 2005 00:13:36 GMT, "tony thomas"
wrote:

~~snippage ~~

Adjust
bow stop tight to the boat. This can be done any number of ways from
sliding the entire bow stop on the trailer to just adjusting the roller on
the stop. Should be able to come up w/ a sliding mechanism fairly easily.

I like that - a very elegant solution.

Later,

Tom

Gary writes:

#1: Am I right in thinking the Coefficient of Friction can not be more
than 1.0

Generally, yes, but "stiction" is another factor.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not
matter as far as
increasing or decreasing the friction?

As an approximation, yes.

"Gary" wrote in message
...

Doug,

Thanks for taking the time.


You need a set of bunks conformed to the hull shape.

Actually, the bunks are formed to the hull quite well. We bolted the
supports on in-place with the boat already setting above the trailer
(on blocks). So they fit darn near perfecty.



I hope that's not true, if so your boat is seriously underbuilt. A
wooden
boat will have stem & keel members, they should be strong enough to lift
the boat much less pull it onto a trailer.


The keel is plenty strong (huge timber). But figuring that the boat weighs
4000 lbs the force to pull on it might be up to, what?, 2000 or more
lbs. And the stem is a seperate part from the keel. I don't know as that
I'd want to be pulling the boat by that. It was built to take pressure
*pushing*
on the keel. But it was never built for the keel to be pulled on.
(Remember,
this boat was built to be LIFTED by the lift rings.)






#1: Am I right in thinking the Coefficient of Friction can not be more
than 1.0


No. Max CFr can be far greater than 1, in theory it can reach infinity.
In
normal circumstances, sliding friction ranges from about .2 to .7

Ok, thanks.


but it can be reduced with substances called "lubricants" and increased
with substances called "glue." Dazzling new technology ;)


Wise a**.




My suggestions- check the weight distribution on the bunks, try to get
more of the weight onto the trailer rollers... try changing the carpet
surface... add a set of transverse bunks conformed to the hull shape...
use slippery bottom paint...


The only roller is the keel roller. the rest of the boat is supported on
bunks
and that's what we're supposed to do with wood boat. Not very possible
to shift any more weight to the keel.

I agree about changing the carpet surface to something like high-density
plastic
that might be more slippery. Also might try that new fangeled "lubricant"
stuff
they make to spray on the carpet.



Fair Skies
Doug King

May the Four Winds Blow You Safely Home,
Gary



Just pull forward at a low speed and hit the brakes. The boat will slide up
in to the bow stop. I do this as is easier than winching and does a better
job. I have the very wide yellow bow roller with the extra rollers on the
outside.
Bill

Your problem can likely be solved by simply changing your retrival technique
at the ramp rather than making significant alterations to the boat or
trailer. Also, rather than trying to determine the exact amount of friction
involved between the boat and the trailer bunks (how many fairies can dance
on the head of a pin?), simply accept that friction is there, it is
significant, and put it to work for you instead of against you, as follows:

Your problem is simply that you are backing your trailer to far into the
water when you retrieve your boat. Since you don't have the ability to
winch your boat to the bow stop, you are instead floating the boat onto the
trailer, up to the bow stop. This works fine until you start to pull the
boat out of the water, when the boat will naturaly settle back a few inches
back on the trailer. Reason? Not enough friction between the boat and
trailer during those first feet of pulling the boat and trailer up the ramp
to counter the effects of gravity and inertia. I have the exact same
problem producing the exact sam results with my boat, but for a somewhat
different reason. My boat has a bow eye and the trailer has a winch.
However the boat alone weighs 12,000 pounds, and there's no way I'll ever
winch the boat across the trailer bunks unless the boat is pretty much
floating free. And if the boat is floating free, then I'll have the same
problem as you when retrieving due to the reasons described above.

The solution is quite simple. Don't back the trailer so far into the water.
Keeping the trailer slightly more out of the water will increase the
friction between the boat and trailer, enough so that the boat will retain
its position on the trailer when pulling the trailer out of the ramp. In
other words, use the force of friction to your advantage instead of trying
to analyze a way to measure it and defeat it. So how do you overcome the
friction to get the boat on to the trailer? Simple, just use the device
that pushed you around the water all day (lots of friction there) and got
you back to the ramp in the first place. Use the engine to power the boat
to the bow stop. It is more than adequate to overcome the friction of the
boat sliding accross the carpeted bunks of a trailer that has been properly
positioned on the ramp, and requires no modification of the boat or trailer,
only modification to the skipper's mindset. Power on, dude.

"bowgus" wrote in message
...
Okokok ... assuming the problem is that the boat is sliding backwards as
you
drive/bounce your way up the ramp, you don't need to pull the boat forward
when you get to the top of the ramp ... you just need to secure it to the
trailer (to the bow-post seems most reasonable) before you start up the
ramp
(that's basically what I do when I power even my little the boat onto the
trailer). Maybe you've got a cleat or two up front that could be used to
do
the job?


It's not that the boat slides backwards.

Interesting idea. Thanks.

RG,

Very nice answer. I'll try it. Thanks.

Gary



PS: As for my trying to understand and frictions, at least part of that was
just my curiosity. I try to use these boating issues/problems as a way to
learn
and/or refresh what I used to know.

On Wed, 16 Mar 2005 15:51:31 -0500, "Gary"
wrote:

RG,

Very nice answer. I'll try it. Thanks.

PS: As for my trying to understand and frictions, at least part of that was
just my curiosity. I try to use these boating issues/problems as a way to
learn and/or refresh what I used to know.

That's odd - I try to forget everything I used to know.

Has to do with storage space you know? :)

Later,

Tom

On Tue, 15 Mar 2005 14:56:12 -0500, "Gary"
wrote:


I hold a double doctoratein phyics.


#1: Am I right in thinking the Coefficient of Friction can not be more than
1.0
In other words, the MAX force needed to pull the boat forward is 4000
lbs.

Yes, that is correct.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter as
far as
increasing or decreasing the friction?

Incorrect. The greater the surface area, the greater the friction.

"Harry Krause" wrote in message
...
On Tue, 15 Mar 2005 14:56:12 -0500, "Gary"
wrote:


I hold a double doctoratein phyics.


#1: Am I right in thinking the Coefficient of Friction can not be more
than
1.0
In other words, the MAX force needed to pull the boat forward is 4000
lbs.

Yes, that is correct.

#2: The boat (painted wood) sets on four carpeted bunks. Am I right in
understanding
that the amount of surface area between the boat & bunks does not matter
as
far as
increasing or decreasing the friction?

Incorrect. The greater the surface area, the greater the friction.


Actually, no. Frictional force =(the coefficient of friction)x (mass) x
(acceleration due to gravity).