Li Ion compared to FLA? Sorry. Not even close. Maybe in some market areas but I can get a VERY robust and durable 220ah 6v golf cart battery for $85. Mine are now over 4 years old and still have actually a bit better than rated capacity. They have been routinely used to 50% SOC and occasionally down to less than 40%. And no BMS or backup BMS needed. One 200a fuse. That's it. Recovered LiIon modules? On a boat? well, okay. As long as your system has some voltage flexibility so if you have to isolate a failed or failing parallel block from the series, you can still charge and operate. I have thought about trying to find electric car modules... the Tesla packs seem to be very nice, but everyone selling seems to think that they are made of gold. And a BMS failure could be well, sort of bad. So as far a Lithium types go, I think it is for me a question of LiFePO4 prismatics or non lithium.
I did once run my boat for almost 6 miles on a 48v 20ah Li Ion ebike battery. That was interesting. I think in a dinghy type situation a portable LiIon pack would be great.
No argument from me, on prop inefficiency. Props are power hungry lazy beasts. At low speeds there are options for optimizing, though. At 2 or 3kts a well designed paddlewheel would work well I think. Got to be slow enough that the paddles are not wasting energy by lifting or throwing water out of the water. At anything much less than 10kts a Kort nozzle increases efficiency, though at 10kts or more the extra drag makes it become less efficient. And of course if you can go deep enough with the shaft, a very large high aspect moderate pitch two blade prop would be wonderful, probably 30% (just a guess so don't bust my chops on this) increase in efficiency over the normal 3 or 4 blade prop, though of course it wouldn't fare well in a grounding or an encounter with a log or sunken piling.
---In electricboats@yahoogroups.com, <gcode.fi@...> wrote :
Excellent post.
Sort of agree on many of your points.
Sort of disagree on some.
If we tie a rope to a tree on shore and pull the boat - vs using the
propellers, we get 4-5x better performance in power/pull/cost.
So propellers are about 20% efficient at best - in general.
The best recovered lion battery modules cost about the same as fla/agm
per usable capacity.
Efficiency is easily seen.
I can push/pull a 70 metric tons 24 m steel powerboat at around 0.5 knots.
My power == 100 W (more like 40W).
Any prop system will consume many multiple of 100W to deliver 0.6 knots.
Sort of agree on many of your points.
Sort of disagree on some.
If we tie a rope to a tree on shore and pull the boat - vs using the
propellers, we get 4-5x better performance in power/pull/cost.
So propellers are about 20% efficient at best - in general.
The best recovered lion battery modules cost about the same as fla/agm
per usable capacity.
Efficiency is easily seen.
I can push/pull a 70 metric tons 24 m steel powerboat at around 0.5 knots.
My power == 100 W (more like 40W).
Any prop system will consume many multiple of 100W to deliver 0.6 knots.
On 30/08/2018 16:13, king_of_neworleans wrote:
> Stick around and read the threads going back over the years. Do your
> homework. It will take you at least a year or two to reach the point
> where you can DIY your electric propulsion setup with a reasonable
> chance of success.
--
-hanermo (cnc designs)
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