torque calculations

my picture looks a bit hard to read

if you cannot read the figures it is 4.5m on the rope, 3.8 m boat length and 95 kg in weight

Thanks

Not that easy unfortunately. Line pull is what you need to start. If you were to lift the pointy end vertically, you would be looking at about half the 95kg. Worst case, call it 95 which is about 950N. Now because the lift isn't vertical, you need the component in the direction of the rope. That angle with the vertical is around 57 degrees, with cosine (trig) of around 0.54. This will make the line pull 950/.54 = ~1760N. Now the torque required is going to depend on the drum diameter / radius of the winch. This is where the T=FxD formula kicks in. Say a 50mm radius (wild guess) 1760x0.050 = 88Nm. I think. Needs a check. Be aware of the different radii that the winch can work at. Also the number may change as the boat goes onto the roof, although I don't think it would get larger.

Hi bungarra, I certainly wouldn't argue with briancc's calculations, the first paragraph left me behind, but maybe try Kevrek, the makers of those small slewing cranes you see on the back of utes and small trucks. The slewing function is performed by a worm and wheel setup. They are usually connected to a smallish hydraulic motor but I can't see any reason why you couldn't drive it with a 12v motor like they use to power the "Powerpak" that drives the whole setup. I would think the smallest cranes (500kg I think) worm drive would do. Maybe give Kevrek a call.


ob

My mental arithmetic says 200KG line pull would be enough, so any 1000LB boat winch will do the job. Aldi had them for about $300. Eric

You could just use a boat winch! with handle, only about 130 Bucks from Bias Boating or super cheap.
Then no worries sorting out power and wiring.

Or hook your 12V electric motor up to the boat winch.

Cheers.