[Public-list] engine rebuild

[John Riley]

Rod Symmes wrote:

>Now you have peeked my interest......
>  
>

Okay, upon reviewing that thread on Renegade-Cruisers, it is a 35 ft 
boat (not 37) and he is switching to dual 72 V motors (not 60) to get 
his power up to where he wants.  His new set-up is due to produce 35 hp 
equivalent.

His Etec 48 V (about 10 HP equivalent) is for sale if you are 
interested.  He claimed it should be good for a 25-27 ft boat, though.

>How powerful an electric motor did you figure it would take ? ( volts, amps or watts ?)
>  
>

I was very excited about his project - a single 48 V motor delivering 10 
hp equivalent with a single bank of batts in series for the propulsion 
(plus another bank for house batts).  It's the trial that I found 
disappointing.  30 amp would suck a single bank of batts (in series to 
give 48 volts) to parade rest in 2-3 hours, unless they are DARN big 
batts (cost + weight), plus the overheating issue on a motor rated at 
120 amp turning at 30 amp.  48 V x 30 amp is 1440 watts.

If you do the straight hp to kilowatt conversion, you'd need about 8 kw 
to sustain 10 hp.  So, if you really need 10 hp on the shaft to push 
your boat at the desired speed in the expected conditions, that means a 
real genset unless you are JUST using the motor to get into/out of a 
slip or some such.  Though there ARE significant efficiency gains in 
using electric with a genset, the weight/space trade-off loses, for my 
application at least.  Still, there are LOTS of reasons to have electric 
propulsion....


But, I'll defer to anyone who does have electrics on board to provide 
comments on their experience.


-- 
John


 1179341986.0