[Public-List] Electric motor conversion

[Kris Coward]

If you shave half a knot off those speeds, they're pretty much in line with what I observed running the electric on Candy Cane (except for the values above 5kW, since I only used a 5kW motor for that repower).

When I did Candy Cane's repower, I only put in about 100-130Ah of battery capacity because there weren't yet any standards for safe installation of lithium batteries on boats, and I figured I could get enough range to get out of a bind from putting in the same weight of batteries as the A4 I pulled to put in the electric (since the electric motor itself weighs about as much as half a tank of gas).

Now that there are ABYC standards for lithium battery installations, if I weren't selling Candy Cane, I figured I'd be looking to put in about 300Ah of battery capacity, which is about half the weight of the lead acid bank currently in place, but about the same volume. I recently picked up 608Ah worth of LiFePO4 cells for the new boat as I'm figuring on gradually repowering her over the next 5-10 years. Since the house bank on the new boat doesn't hold much charge anymore, and I'm highly suspicious that one of the fuel tanks is just waiting to rust out on me, pulling the offending tank and putting in my first 48V battery bank is the first part of this repower that I'm figuring on tackling. Those 608Ah only set me back about C$4.5k, though once I add on BMSes, wires, bus bars, etc., it'll probably hit about C$5.5k, so if you do your own battery work, you can probably get those 300Ah for around US$2-2.5k.

A friend of mine is in the process of repowering a C&C Landfall 38, and has made videos of her repower (including a bunch where she's putting together her own battery banks); her youtube channel is called The Digital Mermaid, if you want to look into rolling your own battery bank. If you go that way and want a pointer to the same cell supplier that she and I are both using, message me off-list.

Cheers,
Kris

-- 
Kris Coward
https://unripe.melon.org/


On Sunday, February 4th, 2024 at 10:27, Hugh McCormack via Public-List <public-list at lists.alberg30.org> wrote:

> Good day all,
> 
> I know that there are some Albergs that have been converted to electric motor propulsion and I am contemplating this myself since the original inboard Graymarine has issues that are not worth fixing.
> 
> In searching through the list archives I have found some useful information but one bit of helpful data seems to be hard to find. This applies not just to Alberg conversions but to those on other manufacturers' boats as well. What I am looking for is a table or graph showing the relationship between motor wattage draw and boat speed through the water and/or shaft rpm (which, with details about the prop, can be converted to boat speed). Has anyone here who has converted to electric propulsion recorded this data for their boat under various conditions?
> 
> One motor supplier gave me the following (which helps to a point but was derived in calm water from a "similar" boat):
> 3.5 knots - ~1000 watts (~20 amps)
> 4.5 knots - ~2000 watts (~40 amps)
> 5.5 knots - ~5000-6000 watts (~100-125 amps)
> 6 knots (hull speed) - ~12,000-15,0000 watts (~250-312 amps)
> Most can only provide motor data from a test bench which has no connection to real operating conditions with influences such as prop pitch/diameter/# of blades, and boat hydrodynamics when motoring into a headwind or in choppy seas.
> 
> Having this data will help me determine optimum battery bank capacity which then determines bank size and associated costs.
> 
> Thanks in advance if you can help.
> 
> Cheers,
> 
> Hugh
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