Hi John.
You're in luck that Catalina 30s are so common, you can find info on the internet that accurately describes your boat and some electric conversions. First let's talk about genreal terms. Being boats, speeds are usually measured in knots (nautical miles per hour). Electric motors are often rated in watts or kilowatts rather than HP. The simplest conversion is 750W = 1HP.
For safety reasons, we generally recommend 1kW for each ton of displacement. Your Catalina 30 has a designed displacement of 10,200 lbs, you're right around 5kW or 6.7HP. Anything larger can use more power without increasing your speed much. Looking at the data page of the "Electric Boat Design" website http://electricboatdesign.com/database/ you can see graphs of performance data for a converted Catalina 30. Using an inboard conversion, Kapowai uses 3200W (4.2HP) to motor at 5kts (5.75mph). A converted outboard may not be as efficient (funny props and set gear ratios), but this should give you an idea about your power requirements.
Running a 48V system, 3200W is about 65A. So now you want to figure out how much battery would support a 65A load for 3-4 hours (as stated in your post), that answer depends on the battery type, I'll give the answer for Flooded Lead Acid (FLA), AGM, and Lithium.
FLA is the cheapest and heaviest answer, you'll need 24.3kWh (486Ah at 50V) to run at 65A for 210 minutes to 60% depth of discharge (DoD). These batteries will weigh about 1100 lbs and cost around $2500.
AGM only needs 18.5kWh (370Ah at 50V) of batteries to run at 65A for 210 minutes to 70% DoD. These batteries would weigh 915 lbs and cost about $4500.
15kWh of Lithium Iron Phosphate (LiFePO4) batteries will run at 65A for 210 minutes to 80% DoD. These batteries would weigh about 375 lbs and cost about $6250 with BMS.
These are only rough estimates in weight and cost, but these numbers will give you an idea of what you're asking for.
Let us know if you have more questions...
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, oak <oak_box@...> wrote:
>
> I'm interested in re-powering (or starting as a backup) my Catalina 30 sailboat with electric.
>
> The boat is used in a Texas inland, freshwater lake - so large waves are not a problem. (For that matter, neither are hurricanes, sharks, or pirates - except the ones that call themselves "boat mechanics"...) I'd like to be able to cruise the boat for a max range of 3-4 hours at 5-6mph. The boat currently has a 30hp inboard gas engine, but I can typically cruise at 5mph at the lowest throttle setting, so I really have no idea how much power would be required to get the boat to 5mph in a fair wind.
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> I've seen the ads for the Torqeedo and the Parsun outboards, but am guessing I need something in the 15hp range from a "traditional gas outboard" to push something of this size.
>
> I like the idea of an outboard. No holes in the bottom of the boat!! Easy to get to without having to pull the boat out of the water. Can be entirely replaced (or at least removed for working on somewhere else).
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> Is it possible to make a larger outboard than the 5-6HP Parsun?
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> If I bought a larger electric motor, and an old 20hp gas outboard, could I "Frankenstein" the two together? That is, can I remove the power head from the outboard, install a large electric, and have a large electric outboard? Has anyone tried anything like this?
>
> Thanks!
> John
>
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