Which Winch?

[Begester]

Is there a formula for determining the winch weight based off of the weight of my boat or do I just use the weight of my boat? I've got a 4600 pound boat and the winches on the iboats website only go to 3200 lbs. Is there something other than the weight of the boat that I use to determine winch capability?

Also - Is steel cable or polyester strap a better way to go? I'll be using the boat in both fresh and salt water if that makes any difference.

Thanks for the help!

 

[marlboro180]

Re: Which Winch?

Generally on a boat of that size, a winch rated for at least half of the boats actual weight ( loaded) will work fine. Unless your launch is really steep , in that case you may want it bit more than that.

The 3200# rated winch would be fine, as one is not lifting the whole weight of the boat, just dragging her up onto the trailer.

Wire rope vs. strap? That is a can 'o worms, and as long as either one is appropriately sized, either is fine. Cables fray over time, and straps wear out due to abrading and/ or sun fade.....choose one.

 

[dingbat]

Re: Which Winch?

I posted this a while back and figured I'd drag it out again.


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 4,600#

Fp = Fg(weight of boat) x sin (20 degrees) = 4,600# x 0.34 = 1,564#

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 = 4,600 x 0.939 x 0.05 =
216#

Then your total winch pull would be:
Ft = Fp + Fd = 1,564 + 216 = 1,780#

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 = 4,600 x 0.939 x 0.5 =
2,159#

Then your total winch pull would be:
Ft = Fp + Fd = 1,564 + 2,159 = 3,723#

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 so I use a service factor of 2 when sizing winches for my boats.

Also keep in mind that they rate winches with an empty spool. The more line you wind back on the spool the less pull per unit input you get out of it. That is why at first a boat is easy winch but gets harder and harder with every crank.

FWIW: My boat is similar in weight to yours. Fully loaded, I run about #5200 lbs. I have a #4200 rule electric winch on the boat. Even at #4200 it very closed to being maxed out. It really whines that last 3' to the post.

 

[rwidman]

Re: Which Winch?

Is there a formula for determining the winch weight based off of the weight of my boat or do I just use the weight of my boat? I've got a 4600 pound boat and the winches on the iboats website only go to 3200 lbs. Is there something other than the weight of the boat that I use to determine winch capability?

Also - Is steel cable or polyester strap a better way to go? I'll be using the boat in both fresh and salt water if that makes any difference.

Thanks for the help!

Others have already mentioned it - you're not lifting the boat, you are dragging or rolling it up an inclined plane. Usually, the manufacturer will specify the weight of the boat that the winch is to be used for.

You cannot go wrong by buying a winch with more capacity than you need. It will cost only a few dollars more and will last longer.

A strap is far better than a metal cable.

 

[gozierdt]

Re: Which Winch?

The size issue is well answered above. I also like a strap over a metal cable. The metal cables are notorious for breaking strands and creating "fish-hooks" that will catch your hands very painfully. The only part of a strap that is exposed to sun damage is the last wrap and the section out to the boat. It's easy to cover that if you're worried about sun damage.

On the other hand, the cable typically gets several wraps per revolution, so the diameter change as you bring the boat up to the bowpost is less- the winch effort is more uniform from start to finish. But on the other hand, the metal cable takes a "set" from being tightly wrapped on the spool, so it's harder to reach out to the boat...

Like almost every topic on the forum, you'll find people on both sides of the issue