GL: Electric boat

[LRZeitlin at aol.com]

TT writes:

I just got a call from a friend attending a trade show.   He said he was at a
booth where they are selling electric motors capable of pushing a 25,000# 
boat
at speeds up to 8kts.   The boat has a large battery bank and two 50amp
multibank chargers.   The chargers are run using a Honda generator which
consumers about 1 gallon of gas every 8 hours.   Anybody have any thoughts
about such a system?
Tommy



I have several Honda EU2000i generators (really invertors) and I use them to
power my boat at night rather than a real generator.   I was just away at a
regatta and ran the thing round the clock.   Average run time per gallon was
8.75 hours, and that included running a full time 5cf refrigerator, 5cf
freezer, tv, and a/c (for one hour).
TT

---------

Tommy,

Something is not quite Kosher with those boat show claims. A 25,000 lb. 
displacement boat running at 8 knots has about the size and performance 
specifications of a Monk 36. Moving a Monk 36 at 8 knots takes about 35 horsepower or 
about 26 kilowatts of electric power. If powered by a gasoline engine it would 
consume 3.5 gallons per hour. With a diesel it would consume 2.1 gallons per 
hour.

If the speed were dropped to 4 knots the required power would drop 
dramatically to 4.5 horsepower. That's 3.36 kilowatts of electric power. The boat would 
use .45 gallon/hr if gasoline powered, for a duration of 2.2 hrs per gallon. 
If diesel powered it would use .27 gallons per hour for a duration of   3.7 
hours per gallon.

Your Honda EU2000i generator (I have one too), running at 8.75 hours per 
gallon cranks out about 800 watts at that setting. That's an average. When the a/c 
and refrigerator kick on the generator cranks out more power. Assume that all 
the power is used to recharge the batteries for the boat's main electric 
motor. To supply the 26 kilowatt hours required for moving the boat at 8 knots, 
the little Honda would have to run for 32.6 hours, nearly a day and a half. To 
move the boat at 4 knots for an hour, the Honda would have to run for 4.2 
hours.

The boat show reps might have implied that the 25,000 lb. boat could run for 
a short period at 8 knots on a full charged battery, say for 15 minutes or so, 
but that's no big deal. A Baker Electric automobile held the land speed 
record for cars in 1900 and could run for an hour on a battery charge.

The current Vetus catalog features a hybrid diesel/electric system for canal 
and sailboats. A diesel engine drives a motor/generator to provide power for 
normal cruising. For harbor use or for quiet slow speed travel on the canals, 
the diesel engine is declutched and the electric motor turns the prop powered 
by a large traction battery. No nonsense about 8 hours on a gallon though.

Larry Z


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