A general comment on battery placement. In any boat you always want the weight as low and centered both fore and aft and port and starboard as possible. The laws of physics are harsh. If you put the batteries aft under the cockpit it will increase the hobby-horsing of the boat and reduce the efficiency as well as make for a rougher ride. Weight in the stern can also lead to a huge increase in drag. The momentum of the batteries accelerating and stopping as they move up and down will cause an increase in drag. Look at your wake from under the stern. It he water is disturbed or "Chasing the boat" the energy to do that came from your boat. When I used to race my J-24 we always put the 3 hp engine below on the cabin sole. Yes that 30 lbs not hanging off the stern made a large difference. That's also why you won't see race sailboats with anchors hanging off the bow and chain stored in the forward lockers. That being said we want to wind up with a livable boat so some compromise between the convenience of hiding those suckers and the safety and performance of placing them amidships must be reached.
Capt. Bill
The Palmetto State
From: Bill Spires <spiresac@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Sun, October 31, 2010 10:07:32 PM
Subject: Re: [Electric Boats] I am thinking about considering building an E-Boat
Thanks for the feedback. I will try to get some pics and post some numbers. I like the Rainbow hull because of it's shape. I believe it will have very low drag at 4kts. I think the stability will be fine with the keel removed and the batteries in with no mast. I want to remove the keel because I want to be able to beach the boat. We have a lot of unpopulated small islands in the lake with beautiful small beaches. With the width of the boat and the fact that the center of mass will be low I think it will be fine but I will perform a stability test to make sure. Reference meta center for more information on the subject of stability. Wish me luck. The square riggers relied on internal ballast and form stability so maybe I can get it to work for me. I really appreciate your thoughts and constructive criticism as they make me consider things I didn't think to consider.
From: danbollinger <no_reply@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Sun, October 31, 2010 10:58:08 AM
Subject: Re: [Electric Boats] I am thinking about considering building an E-Boat
Bill, A word of caution about using sailboats as motorboats. Most sailboats are designed to have poor initial stability, but very good ultimate stability when heeled over. Motor boats are the opposite.
The 1120 pound ballast/keel is half of the boat's 2250 pound displacement , and is partially there to resist the forces of the wind on the sails and provide lift, they are there to stabilize the hull.
Even if you move the ballast inside by using batteries, it might not be enough to make a safe boat. This may or may not be an issue, considering you are using this on protected waters.
The Rainbow hull sketch does seem like an easily driven hull, and there seems to be room to slide batteries under the cockpit.
> I am thinking about building an electric boat and that is why I joined the
> group. I think I have found the perfect hull for me. An old Rainbow sailboat.
> It is currently a complete sailboat but I plan to convert it to an E-boat only
> with no mast or keel. I have a 36 volt golf cart motor but I think I will start
> off with just a trolling motor. The lake I live on is approximately 7 mile s
> wide and 20 miles long with about 600 miles of shoreline. I need about 10-12
> miles of range at about 4 knots. I think a 2 battery setup with an electric
> trolling motor will give me what I am looking for. I will carry a small
> generator to run the blender and provide a supplemental charge. I will
> re-charge the batteries from shore power after a cruise and I am planning to put
> at least on solar panel on with a diode just to keep the batteries topped.
>
> Any thoughts o the above?
>
> I would like to instrument the boat so that I can know exactly how efficient it
> is. If I go for a little sunset cruise how can I tell how many kilowatts it
> will take to recharge the batteries? A spreadsheet that we could just plugs
> some numbers into would be nice,,, and a computer programmed to do all the
> calculations while we are out cruising would also be nice. Tie in the GPS as an
> auto pilot and I can concentrate on running the blender.
>
> Are we having fun yet?
>
> Capt. Bill
> From the Palmetto State
>
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