propshaft driving an alternator , when sailing

[mark0978]

A belt can slip or even be easily cut in case of a problem. A chain drive like that from a bicycle could cause a real problem on top of rusting in a salt environment. I'd stay away from chain drive tied to the engine and propeller.

[Cadence]

Originally Posted by mark0978

A belt can slip or even be easily cut in case of a problem. A chain drive like that from a bicycle could cause a real problem on top of rusting in a salt environment. I'd stay away from chain drive tied to the engine and propeller.

A chain would probably be noisy to some degree. I would bet a Gilmore timing belt would work well. Positive drive without the need for a lot of tension.

[Robert Jansen]

If I remember my engineering formulae correctly, you will maximize the power such an arrangement can generate if the propshaft spins at half of free speed when driving the alternator under load.

[seaforth50]

Hi.
I have been running a propshaft generator for over 20 years when making extended voyages including 2 transatlantics, when it was most useful. The alternator is made by Lucas (special for use) and has the smallest possible input pulley, about 2 1/2" dia. The shaft pulley is about 10" so a good speed up. (When motoring at 5 knots engine speed is 1500 rpm , the gearbox reduction is 2 to 1. The resultant output whilst sailing varies as you rundown the waves and averages 4 amps when sailing at 5 knots. It can maintain the domestic batteries (240 Amphours) at full state when on auto pilot plus freezer, all lights and normal sailing equipment. In case of belt failure there are 2 spare belts, loosely but held clear of the shaft, pre fitted however there hasn't been a failure to date. There is no apparent loss of boat speed.
Its the best piece of equipment on the boat, and I wouldn't want to be without it on long passages.
The boat is a 36 foot 10 ton displacement ketch.
Hopes the above helps
David
David

[gdavydov]

2 solar panels (125 watts each) gives you 250 watts which is about 20 amp 12 volts. Running 4 hours a day gives you about 80ah.

Considering that battery never gives you 125 watts and active sun is more that 4 hours a day you still get about 70-80 AH.

Sigle panel cost about 170-200 on Amazon. No need to purchase special "marine" panels. Solar charger cost about 120-140

So for ~$550 you got the power supply without any wear on shaft. Considering folding or max prop you will get performance and electicity.

Still cheaper than alternator, etc.

[Qayaq]

The good thing about shaft alternators when compared to solar is that they will run your Radar all night and in the morning the batteries are still charged up.

[Jim Cate]

Originally Posted by gdavydov

2 solar panels (125 watts each) gives you 250 watts which is about 20 amp 12 volts. Running 4 hours a day gives you about 80ah.

Considering that battery never gives you 125 watts and active sun is more that 4 hours a day you still get about 70-80 AH.

Sigle panel cost about 170-200 on Amazon. No need to purchase special "marine" panels. Solar charger cost about 120-140

So for ~$550 you got the power supply without any wear on shaft. Considering folding or max prop you will get performance and electicity.

Still cheaper than alternator, etc.

All very well (albeit optimistic) but there are plenty of passages where the sun does not shine all that much, or there is heavy shading from the sails (like N bound up the Oz east coast) or one is in winter with low sun angles and hours per day. Solar requires sun on the panels, and that ain't guaranteed!

I love my solar, but wish I still had the trolling generator I built for our previous boat.

Jim

[john61ct]

In general these days called hydro power correct?

[Cutterman]

It's an attractive idea which I looked into for my boat and decided against for the following reasons:
[*]My boat's average cruising speed is barely five knots due to its waterline length.[*]Tank tests show that revolving props slow boats more than static ones.[*]A revolving prop when sailing wears out the stern gear and gearbox bearings faster than you'd expect.[*]Also, those bearings are not designed to take the lateral pull of belts.[*]There are good hydro generators available designed for the purpose.[*]There is one that doubles as a wind generator.[*]Cost of customising the shaft etc. is prohibitive compared with other solutions.

So I decided to use a hydro generator to augment the solar panels when necessary. Hydro generators can also produce power 24/7 when anchored in a good tidal flow.

I would add that keeping things as simple as possible seems to be one of the secrets to cruising enjoyment but perhaps not to armchair cruising.

Good luck and thanks for all the discussion the question led to.

[Jim Cate]

There is one that doubles as a wind generator.[*]Cost of customising the shaft etc. is prohibitive compared with other solutions.

I can only assume that here you refer to the DuoGen combined wind and hydro generator. It's price is around 2,500 UKP. I reckon that you can modify your shaft and bearings for a bit less than this sum... which doesn't include costs of installation or spares.

And I think you may have a few other mistakes in your post, especially the bit about drag from rotating vs fixed props. That argument has been resolved here and elsewhere many times, and the rotating prop has been shown to be less drag... every time.

But you get to chose what you want for your boat, and in fact I agree that a trolling generator is a better solution than the belted prop shaft for most cruisers. I miss having one on my current boat.

Jim

[Paul Emmanuel]

I crewed for captain Forsyth on his west sail 42 (yacthfiona.com) who had an alternator rigged as you suggest. It gave a steady trickle charge. We monitored the batteries daily, worked like a charm.