Re: [electricboats] Newbie - 20+ foot boat for wide/long river in Guyana, South America

The basic ratio developed by this group almost 15 years ago, and used widely across the industry now is: 1kW/ton to achieve 95% hull speed.  For my boat, Bermuda 30, full keel ketch, 10,800# displacement, that means 5kW should deliver 6kts, and that is right where controlled environment performance measurements have her.  This formula works while in displacement mode only, planing is a different problem, where the energy required goes up exponentially, until you’re up on a plane.  Very few electric boats can do that successfully in practical use.

Keep in mind that for electric, HP to kW comparisons aren’t really relevant.  For Serenity, the 5kW calculates to 6.6hp.  But the 12hp diesel that I removed from her, struggled to push her at 5.5kts at full throttle.

My new (to me) power boat for the Columbia River is of similar weight.  Silver Lining is a ‘78 Glas Ply 28, deep V cabin cruiser that is around 10,000# fully loaded, she cruises at 30kts using around 400hp, from two 300hp gasoline V8.  I would not consider converting Silver Lining to electric.

Electric boats are great, for the correct use cases.  Fossil fuel is much more practical in the way that many people use their boats.  Personally, I do not think that electric will be a cost effective or practical solution for what you have described.

Good luck with your project.

Eric
Camas, WA
Serenity - Bermuda 30 ketch, electric
Witchcraft - F-27 trimaran, gasoline outboard
Silver Lining - Glas Ply 28, twin gasoline inboards

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