Since you're just starting up, I'll limit my answer to some of the very first considerations. Decisions like which prop or gear ratio can't be answered until you make some other decisions.
The two rules of thumb for selecting the size/power of your electric drive for sailing auxillaries are either 1hp electric for every 2.5hp ICE or 1kW rating for every ton of boat displacement.
The hp to hp conversion ratio depends on an appropriately sized and rated IC engine to beging with. While the Atomic 4 was rated to 30hp, in sailboats, the engines rarley produced that much power.
By using your boat's displacement, you can get a much more accurate idea of how much power that you'll need. In your case, you should be looking at motors that are rated for at least 6.5-7kW in continuous use. You need to be wary about some vendor's optimistic power claims of the systems that they are selling. For most installations like yours, building (or buying) a drive system that can produce your needed power without overheating will be the challenge.
As an example, I have a 30" 10,000 pound ketch with a Propulsion Marine 5.5kW drive and that system operates at reasonable temperatures under sustained loads.
Once you've got an idea of a couple of drives that you are considering, bounce your ideas off of the group and we might be able to provide some valuable feedback.
Fair winds,
Eric
1964 Cheoy Lee Bermuda 30 ketch
Propulsion Marine 5.5kW drive, 8kWh Lithium batteries
Marina del Rey, CA
--- In electricboats@yahoogroups.com, merit131 <no_reply@...> wrote:
>
> Hi Everyone out there in electric boats and those of you, like me, will be installing your new electric motor as well. But the question is where to start. It's all new to me and like most, I don't know too much about electric, but the young age of 63, I'm willing to learn. I live in Savannah, Georgia. Just picked up a 1968, 37 Ft Chris Craft, which to me is a very well designed sailboat. If it's still around today, you know it was made well. Yes it has Atomic four engine, which I would like to remove and install electric motor. I've been looking at the kits and chatting with the dealers. It all appears rather easy with these kits. But they all say the same thing. You need a reduction gear, 2-1, 4-1 ratio , and I have been looking into this, but it's not off the shelf, or is it? The prop is another story. I saw some w/ the reduction attached, but costly. I'm a former US Marine on disability so I can't afford some of these. It looks rather simple to build my own. No machine shop here, but I do have tools and I'm ready.
>
> When I talk about dealers or where to get parts or advise, I will try to install links for others. I guess this would help us all. It sure saves a lot of searching on the net.
>
> So here goes, this is what I am dealing with.
> 1. A 37 Ft fiberglass Chris Craft sailboat (Apache) born in 1968.
> 2. Draft: 5'-9" Fin Keel
> 3. Displacement: 13022 lbs, Ballast: 5403 lbs.
> 4. Water Line 26'3"
> 5 Beam: 10'- 2-1/3"
> 6. Prop, Feather type, ( which I think must go)
> 7. Engine: Atomic Four 30HP
> 8. Rig type Masthead Sloop.
>
> If anyone can help with what they think would be the best electric motor for this size sailboat, please feel free to let me know.
>
> If you can also suggest a reduction gear ratio and where I can get it, or the parts to build it, (Pulleys, bushings, etc)
>
> If you could also suggest a prop to make all this work. It will save me a lot of time.
>
> I want to thank yahoo for this site and all the people helping other people like myself. Taking the time out to advise and share their knowledge with dummies like me. Thanks again. Jack
>
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