[Public-List] Electric motor conversion

[Hugh McCormack]

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