Originally Posted by Cowboy Sailer
Atol, how did it work? Did it make very much current
? Did it slow the boat very muck?
it was a standard 80amp 24v alternator
,with a 30 cm pully on the shaft and 5cm on the alt spindle,worked after 5.5 knots boat speed with no appreciable drag.
would have used a 35-40 cm pully if space had allowed to be able to charge at lower boat speed.
on /off control on the field wire,unit was machine sensed so would keep the batteries
at 13.8 volts,and vary output depending what was switched on,ie fridge ,freezer,auto pilot,nav gear
alternator needs 1000+ rpm
at the spindle before it will excite and produce any current,so pully ratios are critical,as is shaft rpm
this one had a 6:1 ratio so about 180 rpm at the prop shaft taking into account the slip on the propellor itself of about 80% ie(if the engine was turning under power rpm would be about 300rpm to achive 5.5 knots of boat speed)
calculations are very critical ,as is a large enough pully on the prop shaft to get the right ratio at the alternator.