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post #1 of Old 12-13-2011 Thread Starter
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Converting my manual windlass to electric! The math is giving me a migraine...

I had a conversation in my head one day as I was sweating up the 500lbs of ground tackle I had overboard with my manual windlass. It went something like this:

"Man, this sucks. It sure would be nice to have an electric windlass."
"Electric windlasses are expensive, and when they die, they seize making the manual backup feature useless. best to stick with the manual"
"This is a lot like hard work"
"Wouldn't it be nice if I had my manual windlass, but an electric motor that was separate (and detachable) to move the lever for me? Then I'd have an electric windlass with REAL manual backup!"

And the idea was born! I had seen something equally hair-brained as my idea in the form of my boat's ridiculous Groco $1,500 toilet. It was a manual toilet but had a similar setup to what I'm proposing whereby the lever arm was attached to a 12v motor on a cam and you could flip a switch and watch the flush lever move back in a creepy haunting kind of way. I'm not too lazy to move a toilet's flush lever, but I am, perhaps too lazy to haul on the lever to pull up 300lbs of chain.

The problem:
What rating of motor and what gear/pulley ratio do I need to attach to the windlass to make this work?

Here is the windlass (exploded diagram):

Even though the hand lever to work the windlass is rotated back and fourth, it is geared such that continuous rotation of either of the handle attachment points can be continuous. IE I can bolt a rotating DC motor to the windlass,(where you would normally insert the lever arm) and away we go. The advantage of doing this is that I can take advantage of the internal gearing in the manual windlass. The question is how much torque/HP do I need and what gear/pulley ratio would be advantageous to use?

Depending on which spot you plug the handle into, there are two gear ratios internally built into the windlass. (For the record the two speeds are: 1. Slow. 2. Glacial.) unfortunately my manual doesn't tell me what the two gear ratios actually are.

My ground tackle weighs 500lbs if it's all out. Where I get confused is the math converting that to torque and how the gears play into it. Torque is apparently not measured in Foot-pounds (which I understand) but rather Pound-feet (which I don't). I doubt I'm generating 500lbs of torque when I move the 5 foot lever back and fourth. How much torque do I need at the flywheel where the lever attaches? For the record I would be attaching the motor to item #5 on the exploded diagram, likely by a belt and pulley, or by toothed gear.

Here is a candidate for a motor to attach. TruckStar Tarp Gear Motor — For 5-Bolt Mounts, Model# 5541095 | Electric Motors | Northern Tool + Equipment
1.3 HP. 40RPM. 836 inch-lbs of torque, 33Amps 12v DC.

I know the math is simple, but I'm getting lost trying to figure out what size motor and what RPM I need.

If I can pull it off, I'll have all the advantages of a bomb-proof manual windlass, with most of the benefits of an electric as well, all for only a couple hundred extra dollars. Anyone able to help with the math here?


P.S. In case you ever wondered, medicine is where all the science geeks who secretly hate math end up.

I have a sauna on my boat, therefore I win.
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Last edited by MedSailor; 12-13-2011 at 12:26 AM.
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