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theller · 26-07-2022, 09:07

Tune in folks... I'm flummoxed by the cost of EV boat conversion kits. Bottom line, it's cheaper than people are pricing it. You could use an ass expensive DC motor and some hot **** "made for marine" system, or you could just do it like a smart little ninja and stick a standard electric car EV conversion kit in. Worried about rust? PCB conformal coating.

So, this will be one of two long running threads for the next six months. My other is my toe rail glass over and deck resurfacing.

Plan.
- 30kw Tesla batteries. Fits in the same space that 800 ah of Lead golf cart batteries were. $900x6 = $3600

- SIMP BMS battery management (can handle 15 battery packs, or 82kwh) - $600
- Battery accouterment (bus bars, contactor, cable... etc. etc.) guessing $1500
- Curtis Curtis 1238-6501 37hp EV conversion motor with controller $3000
- Motor mount - custom job of my own engineering (I'm a ME) that will use the original motor mount brackets and an "infinite" adjustment design $1500

Total ~$10,200

Kicker... keeping my 100 gallons of diesel fuel and putting a 5.5kw baby generator in for a hybrid capable operation. My calculations from the propeller handbook give me a motoring speed of 3.6knots at 5.5kw of power ouput (assuming dead wind). Burning ~0.4 gph, yields 250 hours motoring, 900 miles of doldrums range. Assuming 2.5kw of power input during sunlight hours (50/50) add's ~300 additional miles of range. Probably hold my feet to the fire and degrade all my estimates by 10% for efficiency losses.

Selling my working diesel for a reasonable price and I get my generator for "free"

bcboomer · 26-07-2022, 09:45

Are these LiFePO4 batteries?

theller · 26-07-2022, 10:12

They will most likely be the explode'y 18650 li-ion chemistry until the LFP's start showing up on the used market from newer cars taken out of service.

bcboomer · 26-07-2022, 10:16

Seems like a foolish risk. What about insurance? Insurance companies are apparently looking at lithium batteries and you will likely be uninsurable.

ItDepends · 26-07-2022, 13:06

Great for motoring in and out of your slip, but 37HP is rather underpowered for a Westsail 42.

Works OK (kinda) until you really need it for clawing off a leeshore…

If you put in a 40HP diesel you’d get the same speed performance as with your electric, and a LOT more range. Put in a 55HP, and if you throttled back to 3.5 knots your range would be the same, AND you’d have the punch when you need it.

All that effort, and you haven’t ACTUALLY saved any fuel, except for the piddling bit of solar you add to the mix. The only fuel savings you actually get are JUST from going slower! You can do that with your existing diesel.

Rumrace · 26-07-2022, 13:57

I spent that much in batteries. Go for it.

theller · 26-07-2022, 14:50

Quote:

Originally Posted by ItDepends

Great for motoring in and out of your slip, but 37HP is rather underpowered for a Westsail 42.

Works OK (kinda) until you really need it for clawing off a leeshore…

If you put in a 40HP diesel you’d get the same speed performance as with your electric, and a LOT more range. Put in a 55HP, and if you throttled back to 3.5 knots your range would be the same, AND you’d have the punch when you need it.

All that effort, and you haven’t ACTUALLY saved any fuel, except for the piddling bit of solar you add to the mix. The only fuel savings you actually get are JUST from going slower! You can do that with your existing diesel.

Everything I’ve found, be it wives tales rules of thumb or calculations indicate that you are wrong on your 40hp assertion.

40bhp is probably more like 30 at the shaft after parasitic, tuning and accessory loads and also requires peak RPM.

AC motor has peak torque all the way to rated RPM so prop design is different.

Different design goals. Granted, the numbers may work out to 45hp being the right power output, but aiming for peak diesel output post losses at peak RPM doesn’t honor the torque curve (a line, really) of the electric motor