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 kt.off 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,