"The main/only engine's alternator is 70 amps. How many horsepower is needed for that at maximum drain? "
IF you have a 24V system it will be operating at 28.8V in order to charge the battset.
70A x 28.8V = 2,016 WATTS.
OR 2KW .
Noise maker builders figure 2 hp per KW , but that's for longer life , the actual hp draw is lower (depending on efficiency of generation only about 1.3hp needed) but even at the 2hp/kw , its only 4HP, no big deal with an 80HP engine.
Your Hyd system will take more if its working hard , a good engine drive refrigeration system will be pulling 10 hp into a warm eutetic plate , only 1 or so after a couple of hours.
A cruising AC source , perhaps 4 to 6KW , will drag down the engine more.
Have you sprung the bucks for a CPP ? (controllable pitch prop?)
They are fantastic for economy , but depending on how many hours a year you operate , are usually not cost efficient of anything not commercial.
THE CPP would probably allow you to cruise at 1400 or 1500RPM , good heavy load , low rpm for nice and quiet.
-- Edited by FF on Wednesday 13th of October 2010 08:32:53 AM