Prop-shaft generators

[roly_voya]

Anyone running a prop-shaft generator, what sort of alternator are you using and how well does it work.

I would use a towed water generator, probably an LMV aqa4gen but tow a dingy so potential problems with lines tangling. So thinking about taking the generator and replacing the towed bit with a pully to a large pully on the prop shaft thus using the main propeller instead of the towed one. Thought that using a permenent magnet gen would solve broblems of regulating a conventional auto unit

 

[jeanne]

I have a friend who had a propshaft generator fitted to an Endurance 38. It worked ok, was a bit noisy,and didnt appear to slow the boat too much.
BUT- He has had two failures of the drive shaft system. One nearly sank the boat when a flexible coupling failed half way from the Canaries to the Cape Verdes. This caused the prop shaft to ´Whirl´, and destroyed the prop shaft seal, causing a major leak. The verdict was that the sideways pull of the shaft pulley and the vibration it sets up were the cause of the failure .
I would not do it myself. I wouldn´t tow a dinghy either!

 

[charles_reed]

were quite the rage in the 60s, Hammond Innes had one fitted to his boat.

Most who've had experience of them, to whom I've spoken, wish they hadn't.

Major complaints were noise, leaks and continual wear on prop-shaft and bearings.

Why not stow the dinghy and tow a water generator.

 

[roly_voya]

Good pionts about the engineering, I was wondering about fitting a thrust bearing which would tak the load of the stern gear. Will have to think about noise, this is presumably from the shaft rotating which it will tend to do anyway unless you fit a hefty shaft brake (on one occasion I got 'jump started' sliding down a wave having left a shaft in gear to stop it turning!!) Propshaft should run quite in theory but then the sun should shine in august!

As to the dingy, center cockpit means it wont stow under the boom and aft cabin top has hatch in the middle so cant stow it there. So I am stuck with using a rubber duck or towing a rigid - I like rowing therefore hate rubber duck so am trying the tow. So far its grate and really nice to have the dingy available without having the hassle of blowing it up and launching. So definate plus for coastal but havent tried it on a longer passage yet althou have been out in 30+ winds with no problems.

Thanks for the replies anyway

 

[ytd0]

I had a prop shaft alternator on my 10m sloop in the 70's. Got around the sideways thrust problem by using a chain drive. 2 bike chainwheels on the shaft and 2 small cogs on the altrenator, tensioned with 2 deraliuers.

It was just an ordinary car alternator and residual magnetism was enough to get the field working without a regulator. On a good day it would produce 8 amps, but more usually about 4 amps. Was a pain because I had to slip the chains off before starting the motor as the shaft speed under power was too much for the chains.

Also it was noisy but in a reassuring kind of way. I tried a towed prop to a stern mounted alternator but kep loosing props. Also bring it aboard when enterering port resulted in a huge tangle unless you stopped dead for the recovery.

 

[eyehavit]

My company manufactures water and oil lubricated propeller shaft bearings. Placing a pulley that produces radial thrust ahead of the fwd stern tube bearing to drive a device, <in this case a generator>, sets permanent side (mono-direction radial) thrust against the shaft, in turn placing unwelcome permanent side thrust against the fwd bearing. Propeller shaft bearings are designed to support straight and properly aligned shafts. They do not respond well when a shaft is permanently forced against only one side.
The only way I can see an arrangement like this working is when the side thrust created against the shaft by the pulley is exactly nullified by an equal and opposite side thrust. This may be achieved by running a double -V- pulley and an opposing belt running against a roller bearing.

 

[roly_voya]

Thanks for that - nice to hear someone who likes them! The chain idea is a neat trick but I di whant it to work with the engin as well because then, combined with the main alternator it will feed 150 amps into the inverter which gievs me a 2kw genset for free.

 

[roly_voya]

Yes thought of that one and as part of the instalation will be putting a bearing bolted to a floor forward of the stuffing box both to stop any side load and give the shaft moe support as the new engine will be on flexible mounts rather than bolted down. Also adds security in the event of a coupling or engine mount failure