windmilling a Maxprop

[Ric]

I am speccing out my next boat, a 45ft aluminium deck saloon cutter, on which I intend to embark on an indefinite worldwide cruise, and amongst many desired features are a Maxprop, and a prop-shaft alternator. Are these two goodies totally incompatible? I think I read somewhere that there is a means of blocking (without diving) the blades of a Maxprop so that they do not feather, so that it could be used to turn a propshaft alternator. I think you have to rapidly and briefly put the engine in reverse while the boat is going forward, or something similar. Could anybody confirm this?

I would be grateful for answers before Monday morning as that is when I intend to order my new boat - assuming I win the lottery on Saturday.

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[tome]

I have a Maxprop (3 blade) and it will continue to turn under sail unless I put the gearbox in reverse, which I sometimes forget until I hear it rumble. It does slow you down when turning and I can add 0.5 knot plus by feathering.

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[sailorman]

y not use a row-tow thingy read a report in Yachting World re:- A.R.C.
& it came out very well.

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[jax]

As far as I'm aware (have used a Max prop for 8 years) you can't stop the prop feathering and I think it's not good practice for the gear box to be turning without the engine running. I await condemnation!

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[jax]

As far as I'm aware (have used a Max prop for 8 years) you can't stop the prop feathering and I think it's not good practice for the gear box to be turning without the engine running. I await condemnation!

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[jax]

As far as I'm aware (have used a Max prop for 8 years) you can't stop the prop feathering and I think it's not good practice for the gear box to be turning without the engine running. I await condemnation!

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[gunnarsilins]

I also have a...

...3 blade Maxprop. It does NOT turn when sailing, and I have no possibility to lock the shaft.
And I don´t beleive it could be used for turning a shaft generator, the prop would feather and you´ll lose drive.

And I cannot see the point buying an expensive feathering prop if you are willing to accept the drag from a shaft driven generator.

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[Ric]

Re: I also have a...

Well I'm getting two very conflicting answers here!

I don't think it odd to have both if it is possible - feather the prop if you need a bit of speed and have plenty of coulombs on board, block the prop if you are not in a hurry and need to charge the batteries. Would seem rather nice to me..

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[Witchdoctor]

A propeller is a propeller not a turbine and must surely be very inefficient working to drive the prop shaft instead of the other way round. The aerogen generator thingy which produces power as a wind vane or twice as much when configured as a towed array would be my choice. I bet it causes less drag than a locked prop as well. The best of both worlds as twice the price! It costs over a grand I seem to remember, but if your going to win the lottery anyway... Talking of towed arrays has anyone heard of a neat American gismo which looks like a mini torpedo that you tow behind the boat but it is a self contained reverse osmosis system and the cable you tow it with is in fact a water pipe out of which comes a constant trickle of fresh water. If this trend keeps up all blue water crusers will start to look like trawlers soon!

Julian

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[Ric]

Those things you have to throw out of the back are fine as long as they don't get eaten by a shark or fall off. I like propshaft alternators because they are firmly fixed to the boat. They are a bit less efficient as you say, but they produce a lot more power because the prop is much bigger. I think it would be nice to have one combined with a maxprop that one can elect to sue when needed by the flick of the gear lever.

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[charles_reed]

Why not

Confer with Maxprop - if your Italian is up to it.

It is quite interesting that water-driven generators were all the rage in the 60s and now seem to have very few aficianados. Perhaps the actuality is not as attractive as the theory.

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[Chris_Robb]

Reliability.....

If you are going on an indefinite world cruise - is the Max prop not on complication too far? I think I would far prefer the certainly of a fixed prop rather than an expensive bit of complex engineering with more likelyhood of going wrong.

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[spark]

I visited a man called Greg Powelsland in Cornwall last year who has installed an electric auxiliary drive in his little classic yacht. He uses a Maxprop. When he locks the shaft the blades on the Maxprop feather. When he is sailing in lots of wind with the shaft unlocked the blades on the Maxprop assume the 'astern' position and they turn the shaft and the motor, which generates a charging current. I think he said you sometimes have to give the motor a kick astern to get the blades to set right for regen.

So, yes, the Maxprop will turn your propshaft but how much power you will be able to extract via the shaft alternator is unknown. The bigger the propeller the better. You need to talk to Maxprop to find out the maximum diameter of propeller they recommend for your boat/engine configuration.

I reckon you would want to disconnect the shaft from the gearbox to maximise the output, which will need an additional shaft bearing (you may be fitting one anyway to support the side thrust from the alternator belt). You probably also have to take some care with the battery charging circuitry for when both alternators are running.


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[gunnarsilins]

I don\'t get this!

I NEVER get my Maxprop to windmill, regardless of boatspeed. The shaft is connected to a BW hydraulic gearbox with almost nil resistance.
And I beleive the higher the resistance the shaft makes, the more willingly the prop will feather.
The Maxprop manual says nothing of locking shafts, they just recommend putting the gear in neutral when the boatspeed exceeds a couple of knots to assure proper feathering of the prop.
So connecting an alternator would only make the shaft more hard to rotate - and the prop will probably feather even more easy.
But maybe there is a bit here I don't understand. As someone wrote, best would be to talk to the Italians. And it would be interesting to hear about their comments

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