Shaft generators

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Apetts

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I am told by Volvo that when sailing I should leave the gear leaver in neutral and let the fixed three blade prop turn. Does anyone know of a power generator which can be linked to the shaft so that I can charge my batteries as I sail? If I am going to suffer the wear and tear I might as well get something positive out of it.

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Waste of money...

It just isn't economically viable. Upgrade your regular electrics in preference.

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Hi There,

I read the same thing in the Volvo Penta book, about keeping it in neutral. I simply don't do it. Does this do any harm, or is it just a matter of drag, slowing the boat down?

Swamp Dog

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I am told that when the engine is left in reverse gear, to lock the shaft, there is a possibility of the box jamming and not allowing the gear leaver to return back to neutral position when required. I understand from the Volvo agent that did the last service that this is not an uncommon occurence.

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Bizarrely, research suggests that a locked prop creates less drag than one left to turn, unless there is extremely low resistance (which in practice there isn't). The best solution is as someone has posted above, to have a folding prop. But if you can't do that lock the prop to lessen wear and tear and drag.
 
Lock the prop, less drag. Seems that the biggest problem is having a VOLVO gearbox that requires it to be left rotating in neutral. Get a proper gearbox.

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Our Volvo manual says to put the gearbox in neutral if a fixed blade propellor (or in reverse if a folding prop). We have a fixed 3 bladed prop and as others have mentioned we too lock it in reverse and have never had a problem. On the very occasional time it has been tight to get out of gear a nudge with the starter releases it.

Despite some urban legend to the contrary a locked prop offers less drag. It is also very noisy if allowed to rotate and I do not fancy the risk of using a shaft brake.

John

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Reseasrch doesn`t suggest, it is a physical fact, a locked prop offers less drag.

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Not practicable or economic sense to dish a perfectly good gear box. Just spend the money on a folding prop or let your present prop spin. I would have thought that the effect on the speed of an average cruising boat (unless over a long passage) was negligible and the slight reverberation we experience from the prop, as we break seven knots is quiet satisfying.

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I think the main reason for locking the prop is those of us who are pissed off by:
a) The sheer intrusive noise of the thing, reminding you that you are not a *proper* sailor cos you've got a nice big motor to get you out of trouble, and
b) The anal need to extract the last nano-knot of speed out of the boat, cf. polishing the hull, dabbing at the keel with pots of antifoul when launching, obsessive attention to rig set up etc. etc.

We don't do that do we?

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Fitted to my shaft, ( so to speak) when I bought Tamarind, is a Lucas alternator which generates currents at low revs. At about 4.5 knots we get 3 amps or so building up to about 7 amps at 7 knots. It makes hardly any noise at all and is relatively simple. I cannot fault it. If you need the reference number, reply and I'll get the details next time I'm down

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Trouble is my hydraulic box doesn't lock the prop ..... so I have a spinning shaft .......

I also don't like shaft brakes !


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I came - cos they said was FREE Guinness !
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C\'mon guys ....

Many boaters are DIY 'rs as well as liking to visit the odd chandlers .... To me this post would be a challenge to see if a breakers yard alternator could be rigged via a bolt on pulley to the shaft ...... as the man asks - is there a shaft generator etc. I think because he considers that if the shaft is turning - don't waste the energy put in by the sea to turn it .....

Now where's my nearest breakers yard ?????????


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I came - cos they said was FREE Guinness !
/forums/images/icons/cool.gif
 
Everyone is so sure that a locked prop offers less drag. I have empirical evidence to the contrary.

In 1989 I was part of a crew that sailed 2 identical Catalina 36s from Florida to the UK. It became quite evident over time that the locked prop resulted in greater drag. We let the other boat lead and then used to lock and unlock the prop as a way to control our speed, to maintain a reasonable distance behind them. The difference was small (around 1 fifth of a knot), but it was there nontheless.

Maybe it depends upon the hull shape and displacement.

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Some have emperical evidence that the earth is flat too. By the way, how did you sail so far without falling off the edge?

John

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spoke to vp last year and the techie went to into great detail about how they used to recommend putting in reverse to lock the shaft, however this on occasion locked the box and the only way to unlock was to flick the starter and then it would come out of gear. prob then was that thick owners couldnt do it right so now they say let the shaft turn,
saw a pix of a piggy back alternator above a shaft in one of the comics a while back, looks straight forward enough to make up brackets, secondhand car alternator and away it should go.
stu

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To get a charge from the alternator you need to get it revolving at 2/4000 rpm, you need to check what rpm the prop shaft is revolving at, then work out drive step up required.
The other thing to remember is that the free wheeling shaft requires little power to drive, fit a alternetor that is working, and your towing a few buckets behind, do you have the surplace power when sailing.?
Might work if you look for small alternator, say outboard or motor bike, less output = less drag, a car alternator may stall the prop, low output alternator may be better.

Brian

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My Yanmar does exactly the same. After sailing for several hours with the box in reverse, I assume the hydraulic pressure has reduced to a very low level and the lever is effectively stuck. As you say, starting the engine generates hydraulic pressure and the lever can then be shifted easily.

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