Elementary Question - winch numbers and power

[roger]

I've never managed to understand winch numbers 16, 24 etc.
The numbers go up as the winches get bigger. What numbers indicate the mechanical advantage?
As the drum gets bigger the mechanical advantage goes down unless gering or winch handle length goes up and that seems unhelpful as one presumably needs larger winches for bigger loads.
Clearly I dont understand the system - please explain.

 

[gandy]

On modern winches the number indicates the mechanical advantage. As you say, the gearing changes. For example a Lewmar has a gear ratio of 2:1, whereas the Lewmar 30 is 4:1 or so.

On older winches, I don't know what the numbers mean. Ours are Lewmar 10s, which have a power ratio of around 7, and they're bloomin hard work on the wind.

 

[stephenh]

try this :

http://www.ybw.com/forums/showflat.php?Number=1317639&page=0

It appears that different manufacturers have different ways of naming...

 

[William_H]

Hi Roger your logic is totally correct for non geared (single speed) winches. The power advantage is dictated by the drum diameter related to handle length. Yes a bigger drum is needed for bigger rope as used on a bigger load so a much bigger handle needed.
As soon as you go to geared winches then the gear ratio comes into the equation. Winch number seems to relate to the size of the winch/ size of the job and not to any formular. olewill

 

[roger]

Thanks stephenh and William_H, I begin to get the message. In fact when the manufacturers talk of power , they should be talking about velocity ratio - 40:1 means the velocity of the rope coming in is 1/40th of the velocity at the handle end. The power advantage will be reduced by an uncertain amount of friction. The power/velocity ratio can I presume only apply to the maximum gearing. Nobody uses handles 40 times longer than the winch radius ( 4 inch dia drum with 80 inch handle)
Next time I get to the boat (May) I'll check on the ratio and see what might be suitable. Again thanks.