Sizing my winch

[diskord]

So I have just purchased a 16 ft '66 Reinell runabout with a Mercuy 1000 thunderbolt on the back. The trailer that came with the boat is in need of some TLC, and one of the things it needs is a new winch. I found a bunch of manual winches here on iboats for sale, but I have no idea what weight I need for my winch.

The tongue weight on my trailer is under 100 lbs, but I know that is from a balanced load, while the winch is pulling the entire weight of the boat up. Also, the trailer has rollers, if that makes a difference on how hard/easy it is for a winch to pull up.

Most of the winches in the 1200-1400 range are pretty reasonable, but you hit that 1500 range and the prices really start to jump... do I need a 1500 lb winch?

The other thing is I am pulling my boat (mostly) laterally on to the trailer, not pulling it up a cliff, so even if my boat is 1500 lbs, do I need a full 1500 lb winch, or just like a 1000 lb winch?

Thanks for any tips/advice.

 

[Treager]

Re: Sizing my winch

I'm not sure how much the boat weighs, but lets assume it is 2200lbs with 200lbs for the motor.
If you were to pull it straight up, you would need a 2500lbs winch with appropriate rated strap (working load).

If you're pulling it up on rollers, I think a 1200-1400lbs winch would be fine, even on steep boat ramps (just keep in mind that the strap, will over time, weaken due to exposure and should be replaced if it shows any kind of wear, frays or other defects). If you had bunks, I would suggest slightly higher because you would be working against friction and gravity.

 

[rockin ronnie]

Re: Sizing my winch

for the most part you will be pulling your boat in water onto a trailer that will be in water like treager said 1200 to 1400 lbs would work fine and if you was to get a two speed would add to the pull or at least take less to crank and for about 50 northerntool.com has a 1800 lbs two speed itam number 148821-2006 that mite be the answer good luck

 

[dingbat]

Re: Sizing my winch

The first thing you are interested in is the winch pull required to overcome the 20-degree slope. For this example, let?s use your boat weight of 1,500#

Fp = Fg(weight of boat) x sin (20 degrees) = 1,500# x 0.34 = 510#

We now then need to account for the friction between the hull and the surface of the rollers or bunks. This is where things get complicated. The Coefficient of Friction (Fn) can vary tremendously due to a number of variables. For instance, a set of well-lubricated rollers and a smooth hull you can have a very small "Fn" of say 0.05. Bunks vary from @ 0.07 to 0.2. A damaged roller or a lifting strake on the hull that has to pass over a roller and you can easily push the "Fn" to 1.0 or higher.

The weight of the boat is multiplied by "Fn" to determine the mechanical friction associated with winching the boat on the trailer. For this purpose we?ll use a minimal value of Fn =0.05

Fd = Fg (weight of boat) x cos (20 degrees) x Fn = 1,500 x 0.939 x 0.05 =
70#

Then your total winch pull would be:
Ft = Fp + Fd = 510 + 70 = 580#

But add in a lifting strake to overcome and this need will sky rocket

Fd = Fg (weight of boat) x cos (20 degrees) x Fn = 1,500 x 0.939 x 0.5 =
292#

Then your total winch pull would be:
Ft = Fp + Fd = 510 + 292 = 802#

This is the easy part. The hard part is selecting a winch that is'nt going to break your back supplying this #802 lbs of pull. I personally would look at a winch that would supply twice this number.

 

[Lion hunter]

Re: Sizing my winch

The first thing you are interested in is the winch pull required to overcome the 20-degree slope. For this example, let?s use your boat weight of 1,500#

Fp = Fg(weight of boat) x sin (20 degrees) = 1,500# x 0.34 = 510#

We now then need to account for the friction between the hull and the surface of the rollers or bunks. This is where things get complicated. The Coefficient of Friction (Fn) can vary tremendously due to a number of variables. For instance, a set of well-lubricated rollers and a smooth hull you can have a very small "Fn" of say 0.05. Bunks vary from @ 0.07 to 0.2. A damaged roller or a lifting strake on the hull that has to pass over a roller and you can easily push the "Fn" to 1.0 or higher.

The weight of the boat is multiplied by "Fn" to determine the mechanical friction associated with winching the boat on the trailer. For this purpose we?ll use a minimal value of Fn =0.05

Fd = Fg (weight of boat) x cos (20 degrees) x Fn = 1,500 x 0.939 x 0.05 =
70#

Then your total winch pull would be:
Ft = Fp + Fd = 510 + 70 = 580#

But add in a lifting strake to overcome and this need will sky rocket

Fd = Fg (weight of boat) x cos (20 degrees) x Fn = 1,500 x 0.939 x 0.5 =
292#

Then your total winch pull would be:
Ft = Fp + Fd = 510 + 292 = 802#

This is the easy part. The hard part is selecting a winch that is'nt going to break your back supplying this #802 lbs of pull. I personally would look at a winch that would supply twice this number.

YEAH, What he said

 

[marlboro180]

Re: Sizing my winch

Dingbat- I vote we make post of yours that a sticky here in the trailer section!!!

 

[NelsonQ]

Re: Sizing my winch

Dingbat- I vote we make post of yours that a sticky here in the trailer section!!!

Absolutely....+1 for sticky on getting that for sizing a winch...

 

[ezmobee]

Re: Sizing my winch

Without doing math I would think just about any winch would work for your small boat. However, if you want to step it up, find the largest one they make before they start being dual-drive gear reduction, cuz you definitely don't need that and you'd be cranking forever.

 

[dingbat]

Re: Sizing my winch

The reason I posted the formula was to show the influence that "Fn" had on the amount of pull required. It clearly demonstrates that the amount of pull can vary widely depending upon a number of variables that change with each application. Anything other than a measured "Fn" value is guessing and an uneducated guess can be as good as picking numbers out of a hat.

Having said that, what the formula does demonstrate is that 1/2 your boats weight is in the ballpark when it comes to how much pull is required. This is only the pull necessary to winch the boat on the trailer. This figure does not include a service or safety factor that you should include when sizing a winch.

Service factors vary between 1.5 and 2.5 depending on the application. For a boat winch I would use 1.5 minimum. "Bigger" is never too much when sizing a winch. I use a service factor of 2 when sizing winches for my boats.

 

[Treager]

Re: Sizing my winch

Absolutely....+1 for sticky on getting that for sizing a winch...

+2 for sticky (thanks Dingbat)