Hi Myles,
This thread is missing a lot. And your estimate is overstated. 15kW (208A * 72V) would drop a 500# Flooded Lead Acid (FLA) battery pack to 60% Depth of Discharge (DoD) in 12 minutes or just over 1.1nm. So this part of the conversation is a non-starter.
Let's start with the hull specs. 2.4 tons and an 18.5' waterline. Simple theoretical hull speed is about 5.75kts. So 2.5kW (3.3hp) should drive the boat to 90% of hull speed, i.e. 5.2kts. Pushing at 5kW (though a properly matched system) should deliver better than 5.6kts. Pushing at 10kW, might increase the boat's speed by 0.1kt, Pushing at 20kW will likely deliver no more speed than 10kW.
So there is virtually no reason to install anything larger than 10kW (13.3hp) and practically, a 7.5kW (10hp) drive should be sufficient for all but the most extreme conditions.
If we assume that cruising speed is 5.5kts (95% of hull speed), the power draw should be right around 4kW. Does anybody here that already has an electric boat cruise at 95% of hull speed? Not as far as I know. I would suggest that cruising at 2.5kW or 5.2kts is a little more reasonable for an electric drive. So let's figure range/duration for power settings of 2.5kW and 4kW against various 500# battery packs.
500# of FLA batteries should have a rating of 11.3kWh (225Ah * 50V) and may cost around $1200. This pack would have 6.7kWh usable to 60% DoD.
500# of AGM batteries should have a rating of about 10kWh (200Ah * 50V) and may cost around $2500. This pack would have 7.1kWh usable to a 70% DoD.
500# of LiFePO4 batteries should have a rating of about 20kWh (400Ah * 50V) and may cost around $10,500. This pack would have 16kWh usable to an 80% DoD.
FLA would deliver the following ranges (including Peukert's Effect):
5.2kts or 2.5kW = 110 minutes or 9.6nm
5,5kts or 4.0kW = 61 minutes or 5.7nm
AGM would deliver the following ranges (including Peukert's Effect):
5.2kts or 2.5kW = 143 minutes or 12.4nm
5,5kts or 4.0kW = 85 minutes or 7.8nm
LiFePO4 would deliver the following ranges (including Peukert's Effect):
5.2kts or 2.5kW = 374 minutes or 32.4nm
5,5kts or 4.0kW = 230 minutes or 21.1nm
While there are some basic assumptions made to come up with these numbers, I'm guessing that real world performance will be surprisingly close to these predictions. Of course, these numbers assume a properly engineered and matched drive system (from batteries all the way through the prop), a poorly engineered, home-brew solution may not deliv er the same estimated speed and range.
Fair winds and smooth seas,
Eric
Marina del Rey, CA
No comments:
Post a Comment