[Public-list] weight distribution and electric power

[isobar]

>===== Original Message From dan walker <dsailormon at yahoo.com> =====
>  i was told i can motor 25 to 50 mile before empty. supposedly th batts will 
recharge as i sail. the system has "smart" chargers that i am to plug in while 
at the dock. i wont know until next springs sea trials how well any of this 
works. the owner of the company is an electrical engineer and a horrible 
salesman. that helped a lot in my decision to give the asmo a try. will report 
in---good or bad when i REALLY know the answers from experience

=====

Dan
 Maybe the owner is vague not because he’s a bad salesman, but because 
he’s a good one.

25 to 50 miles isn’t clear unless you know the boat speed. Remember that 
pre-nuclear submarines could travel  for over a day at 2 knots on battery, but 
only about half an hour at 18 knots. Your range is strictly governed by motor 
current draw at various loads,  and your  engineer/salesman should be able to 
give you a graph of that.

Take some back of the envelope calculations: How much energy does it take to 
push an Alberg thru the water at 5 knots? Guess 8 HP minimum – think of a 9.9 
HP outboard bolted to the transom. – someplace in that ballpark. That’s 6 
kilowatts or 6000 watts. With a 48 volt system (same energy as for a 12 V 
system), that’s a 125 amp current draw.

If your regenerative braking prop gives back 1 amp @ 48 Volts while dragging 
thru the water at an average 4 knot sailing speed (Generous estimate), then 
the 125/1 ratio means you’d have to sail for 125 hours to recharge 1 hour of 
motoring.

If you have a 25 mile range at 5 knots under power, that’s 25 miles/ 5 mph = 5 
hours X  125 amps = 625 amp-hours worth of battery capacity you’d need on the 
boat. How much does that weigh? I don’t know about the capacity of 48V 
batteries, but that’s the equivalent of  over 25 Deep-discharge 12V batteries.

All the above is guesswork, and I could very well be wrong, but you might ask 
the questions.

Bob Kirk
Isobar #181


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