Hi Sean,
There are two different rules of thumb for converting ICE to electric drive. The first is based on the HP of the existing engines. Typically, you can convert HP at 2.5-3HP ICE to 1HP electric. Using this conversion, each of your 30HP engines can be replaced with 10-12HP motors or 7.5 to 9kW drives. (1HP = 750W). The problem is that this conversion is dependent on how well the IC engines were sized to your boat.
Alternatively, most displacement boats typically require 1kW for each ton of displacement. So using that conversion your 9 ton boat would need 9kW of total drive to power at 95% of regular hull speed. However, your catamaran desn't act just like a regular displacement monohull, and cats typically have more windage than a monohull of similar displacement, so your power requirements will probably be higher.
So while I believe that 9kW is too little for your boat, you should get safe propulsion to reasonable speeds with 15-18kW of electric drive as listed in the first paragraph.
Hopefully Steve, a member here with an all electric 41' cat, will weigh in with specifics about his boat, I think that you would see similar results with similar drive units.
I believe that pods look good onthe design board, but some pod owners have reported problems with pods that are submerged 24/7. Many successful electric conversion have been done with inboard style drives, retractable outboards or drive legs have also worked well. I'm not saying that pods are inherently bad, but they haven't built a solid reputation to date. Properly designed and executed pods might be able to change that perception, but the cost might be higher than some of the regular electric drive conversions.
Welcome to the group!
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "seansullivanjobs" <seansullivanjobs@...> wrote:
>
> Still working on this design...
>
> I'm exploring the use of off the shelf, submersible electric motors to spin props (pod style) for a 45' sailing catamaran with a max loaded displacement of 18,000lbs.
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> Could anyone help me figure out how to convert the twin 30HP Yanmar diesels that are specified to the appropriate HP or KW of electric motor?
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> I had thought it was about 15-20KW electric, but had this whole debate on and electric unfriendly forum where they kind of sand bagged me.
>
> Can you guys help me figure out what the appropriate electric motor sizing is to replace a 30HP Yanmar 3YM30?
>
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