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.
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 doubt I'm generating 500lbs of torque when I move the 5 foot lever
You could make make 500lbs with one hand tied behind you r back with a 5' lever :)
If it was me i would look at what you could buy and see the power it draws and the input and output speeds of the motor and work from there ;)
Quoting only part of OP.
To clarify ... ours was a through deck model so the motor was accessible from a locker in the forecabin. Our new girl has an ondeck type, though it is mounted inside the anchor well. I've not looked at access to motor on this.
I'm basing my fears on another formosa owner who had his pack-up and seize on him 1/2 way into a 6 month trip. I suppose if I end up shelling out for an off the shelf model I'll look at how easy it is to disengage the electric motor....
I fiddled a little with the windlass today and was able to ascertain the gear ratios by seeing how many turns of each handle attachment point were needed to turn the wildcat one full turn.
Looks like "high speed" is 1:1
and "low speed" is 2:1
Hmmm.... Even though the diagram is chock FULL of gears it looks like most of the mechanical advantage is probably from the lever in my hand. Not good for my cause me thinks. Also the cold grease packed into the unit provided quite a bit of resistance itself today. Could barely turn it with my hand and no chain load at all.
So how many inches of chain move per rev of wildcat? Times 40 rpm(on direct drive shaft)divide by 12in/ft. Can you handle chain coming in at that rate? That is max no load speed. If that is too fast put the motor on low gear I would think over one hp is more than powerful either way.You still need to figure how to quick disengage the unit. Dog clutch, syncro rings from old tranny , or hex the shaft to5/8 and square the other and connect with a 1/2 drive socket.Keep the adapter plate wing nuts loose. There are many ways to haywire this together.Some will look good on the foredeck.
If I were you I'd shell out on a new one. When you head off crusing you are going to spend an awful lot of time in unknown anchorages. For mine that means getting the hook up without killing yourself is a major priority.
Our new girl has a Lofrans than seems capable of pulling up anything and even the old girls Muir, once rebuilt has performed faultlessly. Its quite amazing the wreckage we have pulled up from the deep.
Unless you're tackle is hanging off the bottom, you're not really lifting the entire weight at any given time.. If you motor up on the hook you should only be lifting the chain that is equivalent to your depth... but of course you may one day slide off a ledge and indeed have everything hanging...
How about adapting these newer hi torque battery drills? Enough power there?
ok, I'll chime in.... torque= foot pounds. Let out as much chain as you like. Connect a fish scale to the arm. start to pull in the chain with the fish scale. see how many pounds it takes to lift the chain. multiply the pounds by the lever arm, eg, 50 pounds force times a 18 inch arm (1.5 feet) equals 75 foot pounds....so that's what you need to move the chain.... a good place to start... all winches have different co-efficients of friction...if you now "connect" a motor with those specs, the chain will rise....
My point is that MedSailor is planning on a long tem cruise not simply a weekend here or there.
Get yourself down into the South Pacific where there are anchorages with depths of 100' and then pull the anchor up by hand.
For long term cruising in a 40 plus foot boat you need not only great ground tackle but a bloody efficient method of hauling the thing back up on deck.
We actually managed to hook onto a sunken trawler once. The part of the things bridge that came to the surface and had to be cut away from our anchor weighed well over a 100lbs. Without our lovingly repaired windlass I would never have got the thing to the surface and would have either been forced to cut the chain or stay hooked on and dive or get a diver to go down. Our windlass was able to bring it to the surface and hold it in place while I cut away the debris with bolt cutters.
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