Denny,
I found a good article that explains the effects of Peukert's Law in detail and includes an effective formula for predicting the potential capacity of range of a large battery pack.
http://www.smartgau
Using their formula of T = (C/(I/(C/R))
16 T-105 batteries, $2240 and 1000 pounds, 22.5Kwh total and 13.5Kwh usable capacity:
4mph - 11A @ 48V = 25.5 hour capacity and 102 mile range
8mph - 100A @ 48V = 1.56 hour capacity and 12.5 mile range
A similarly rated AGM battery bank will weigh about 20% (200 pounds) more, cost about twice as much, but the Peukert exponent drops to 1.1 which gives the following results:
4mph - 11A @ 48V = 26 hour capacity and 104 mile range
8mph - 100A @ 48V = 2.3 hour capacity and 18.5 mile range
While the slow speed range doesn't change much, the AGM batteries can deliver almost 50% more range at the stated higher current loads.
For an exotic solution, LiFePO4 lithium batteries have a Peukert exponent of only 1.02, weigh less than 50% of AGM, are half the size, cost twice what AGM cost but will support more than 1000 cycles at 70% DOD. So a 22.5Kwh bank would have 15.8Kwh usable and weigh 550 pounds. The results would be as follows:
4mph - 11A @ 48V = 30 hour capacity and 120 mile range
8mph - 100A @ 48V = 3.2 hour capacity and 25.4 mile range
So, LiFePO4 can deliver twice the fast range at around half the weight and half the size at 4 times the cost of wet cell batteries. There is some, but not as much of a difference at lower current loads (slower speeds).
These calculations do not factor in any increased or decreased performance due to changes in the overall weight of the boat, but one can assume incremental improvements in range and speed as the weight goes down.
Fair winds,
Eric
SoCal
--- In electricboats@
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> ... I could see a long narrow light hull ( a catamaran would be even better) optimized for a speed/length ratio of perhaps 0.6. A boat with a 30' waterline length, weighing 3000# with (16) 220ah 6v batteries could go 140 miles at 4 mph.(11 amps at 48v) 100 amps would give 8 mph for 22 miles. Total battery weight would be about 1000# and cost maybe $3500 for top of the line AGMs. Maybe 1/3 that for wet batteries. You could cut the bank size in half in you were happy with less E range or more reliance on a gen set.
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> Denny Wolfe
> www.wolfEboats.
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