sizing a winch for boat trailer

K-2

Chief Petty Officer
Joined
Apr 3, 2011
Messages
406
I see boat trailer winches are sized by pounds. Is there a formula to help get the correct capacity?
Thanks!
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
There is another side to the question, The YOU factor.
The winch may be able to handle the load, but can You handle the winch?

Assuming a 1000# boat for example....

Pulling onto a set of Lubed Bunks will produce about 25% friction. ~250# ... More if Dry.
A 15% boat ramp will add another 7% due to the slope. ~70# ... 320# total. 32% total weight.
So a winch rated at 50% of the load should be well within its rated capacity.

Winches are commonly geared at ~5 to1, the ratio of a full spool to the size of the crank handle is about 3 to 1.
This gives you an additional 3 to 1 advantage. A good thing! 3 x 5 = 15
This gives the winch about a 15 to mechanical advantage overall.
So producing the 320# of pull will require You to crank with 320/15 = ~21# of force on the handle.
Or about 2% of the load. If the boat weights 3000# you will need ~60# of grunt to keep it moving.

A 1500# winch will easily handle the load.
But cranking the winch will be like bench pressing 60#, 20 time in a minute.
Ever wonder why you nearly have a stroke cranking that winch? Now you know!

2 stage winches commonly have 5:1 and 15:1 gear sets.
x3 of the crank advantage yields a 15:1 and 45:1 overall advantage.
Once the standard 15:1 get too hard to crank, you down shift to 45:1 and keep going.
60# becomes ~20# again! ~7# per 1000, Or ~0.7% of the load

I have a Fulton-F2, 2 speed winch, that allows the 69 year old Admiral to recover an 18ft 3000# bow-rider with ease.
Her idea! She won't let anyone help!
We usually get an audience at the ramp once they notice the lady is cranking the winch.
She occasionally gets a round of applause!

No one ever complained that they bought too BIG a winch.

If you are considering an electric powered winch, there are more factor other than pulling power that you will want to consider.
 
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gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
Not to throw a cog into the gears (bun not intended, but it does fit :smile:), but there is another issue you may want to take into account as well. A friend of mine one day was at the ramp and already removed the winch strap from the boat (not a good idea) and was backing down the ramp when he stopped. But the boat didn't stop, and dropped on the ramp well ahead of any water. To say the least he had to put that boat back on the trailer. So now that winch has to pull so much more weight to winch it back on the trailer. The entire weight of the boat is now in play (at least a lot more of the weight anyways) So make sure you figure out for such certainly unusual events when addressing a winch. Needless to say all the other boats waiting inline for their turn at that ramp were not too happen with him that day. There were only two ramps and the "crappie" were suicidal as well that time of the year... Just some food for thought! JMHO!
 

Starcraft5834

Lieutenant Commander
Joined
Jun 2, 2013
Messages
1,677
+1 ^^^
Go Big,or you might Not go home! :lol:

2/1 ratio. 5000lb boat= 2500 winch... with that said.. I'd agree with Willie... "better to have and not need than need and not have"... don't bring a knife to a gun fight... make sure by going a little heavier...and use a strap, not cable...Ive had both..strap is way to go
 
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Teamster

Lieutenant Commander
Joined
Nov 8, 2010
Messages
1,923
When I've needed to replace them in the past I always bought way bigger than I thought I needed,

And always get a two speed winch,...

Never know when you'll put in on a steep ramp and that can come in handy,...
 

DodgeBoy

Cadet
Joined
Feb 8, 2015
Messages
8
Why a strap and not a cable. Assuming the cable attaches to the strap and is only going to the boat right. BTW new be boat owner, have been around them all my life just have never owned one before.
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
The Strap is not attached to a cable. It completely replaces the cable. Strap OR cable. One or the other.
Cables gets kinked, don't spool up evenly, and eventually rust. Strands break and draw blood.
Straps are seat belt webbing. Soft, flexible and spool nice and flat. A much more friendly material.

Not that you should ever expect that either will break under a load...
The strap will give you plenty of warning and do a lot less damage to whatever it hits.

Other than an a slightly higher, if any, cost, there is not much to dislike about a strap winch.
 
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