Converting 2x9.9 HP outboards to electric


100 µW
Jan 9, 2020
I'm super curious about hybrid propulsion (electric drive, fossil fuel generator for range extension). I have a Seawind 1000 XL2 powered by 2x Yamaha 9.9 high thrust variants. I'm searching around to see if any outboard would fit there. In addition, I'm planning for the propulsion battery bank. It'll serve as a propulsion bank but also as a house bank for the AC inverter and powering the 12V via a Victron B2B (step down to 12V with a dumb converter and use Orion Smart Tr to charge the 12V system). A 12V battery remains necessary to power the windlass.

  • 35ft lightweight catamaran (Seawind 1000 XL2)
  • Rated for max 2x10kW engines, so design for 20kW continuous discharge (although will be less than that in reality).
  • Aim for 1h range at full power (20kWh).
  • Obviously 48V nominal for this power requirement. I don't want to go higher than 60V.
  • Price is a lesser concern, since it's overall not a big differentiator in the overall project.
  • Delivery to California (SF or LA).
  • Available volume is two compartments of dimensions 890mm (length) 250mm (width) 41mm (height).
  • Weight is a concern, so aluminum encased cells it is.
  • Cost is not a primary goal (will pay extra to make it work).
Right now the contenders are:

  • CATL 302Ah in 2P16S: 185Wh/kg, 167kg, 30.9kWh
  • CALB L173F230B in 2P16S: 175Wh/kg, 134.4kg, 23.6kWh
  • Fortune 205Ah in 2P16S: 156Wh/kg, 134.4kg, 20.9kWh
The Fortune could seem a clear loser here, but they gain extra point in my book for being so easy to assemble and work with.

Here's my notes so far (see "Mothership: LFP cells"). The BMS is a Rec Q 16S. Busbars and distribution is Victron's Lynx setup with Cerbo GX and Multiplus II for main charge source.

Actual engines will probably be ePropulsion Navy 6.0, although their long shaft variant is a bit too short. There's also the Elco 9.9hp but they don't do hyro-generation, which I expect to be a significant source of charge (we average 7kts sailing). Current engines are gas Yamaha 9.9 outboards with extra-long shafts (25"). I'll figure out some story for "range extension" later. We have gasoline tanks onboard so the easy way is to use Honda EU2200... but I don't like the smell of gasoline. And yes, it's unclear whether this is all a good idea or not, but I want to try it out so

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I guess there should be a question: do you know of any cell I should evaluate here that's not in my spreadsheet? And where would you buy them from (I live in California, residence in SF area, boat is in LA). Also, do you know of outboards that would work with 25" shaft requirement?

cross posting from Cruiser's Forum at