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sherbet 08-11-2003 10:13 AM

the lowdown on free-wheeling shaft generators?
Does anyone know where I can get a detailed evalution of generators that get their power from the free-wheeling shaft spinning while you are sailing?

output, effect on engine/shaft, speed necessary, etc.

I have the books by Don Casey and Nigel Calder but both just gloss over them.

GordMay 08-12-2003 02:34 AM

the lowdown on free-wheeling shaft generators?
For starters:
1 Horsepower = 747 Watts at 100% efficiency.
Watts = Volts x Amps, and Amps = Watts / Volts.
Read the equipment specifications, and you can calculate the minimum (it''ll likely be about 50% more) H.P. drag the generator will impose.
These devices, in my opinion, are not usually worth the capital & operating cost. Operating cost, you ask? Any machinery requires maintenance & repair, both to itself & to it''s associated machinery. There''s no free lunch!

mdougan 08-12-2003 09:12 AM

the lowdown on free-wheeling shaft generators?
Search the old Sailnet Articles. They had a pretty detailed write-up maybe back in February or March.

fourknots 08-12-2003 11:16 AM

the lowdown on free-wheeling shaft generators?
FWIW, I have a water powered generator for sale that hangs off the back like an outboard motor. It''s basically an alternator geared to a housing that looks like a small outboard. Not much maintenance and decent power. If interested, email at

ARCA 08-12-2003 03:56 PM

the lowdown on free-wheeling shaft generators?
I have a shaft charger on my AMEL Santorin (14m). This was a standard piece of equipment on all AMELS until about 5/6 years ago. It can be switched on and off as required. Under about 4 kts it really produces little power and takes around 1/2 boat speed. After about 4 kts it progressively puts in more amperage - around 5 amps at 5 kts and I have seen 16 amps at 8/9 kts. Effect on speed diminishes the faster you go. It cannot be used when the engine is running as it cannot be run when the alternator is running.

Hope that this is of some use,


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