Positioning of batteries COG effect on Sailboat Center of Balance

[ButchL]

I have a full keel sailboat "GlenL Amigo" LOD 22ft 2 inches, LWL 19ft 2 inches, beam 8 ft 3 inches, Center of balance 9 feet forward of stern waterline, weight 5500 lbs, ballast 1775 lbs. I plan to secure eight 6 volt batteries (Total weight 512 lbs) in two plywood boxes (four per box) to the keelson. The center of gravity of the batteries will be 3 feet aft of the COB of the boat. The top of the batteries of the aft box (which will be where the inboard motor would have been) is approx. 5 inches below the waterline. The batteries in the second box forward of this is approx. 8 inches below the waterline. The Ray Electric motor will be mounted on the stern (Total weight of electric motor and motor mount is 140 lbs).

This is the only practical place for the batteries. Since my boat is in my backyard, I am unable to test how the batteries and motor COG effect the balance of the boat before I secure them.

Calculating moment (not including interior structure or equipment) (9 ft x 140lbs outboard motor) + ( 3 ft x 512lbs battery) gives me 2796 moment aft of the COB. That would mean that I would need 466 lbs 6 feet forward of the COB, or 349.5 lbs 8 feet forward of the COG to compensate.

Since the batteries are below the waterline and battery COG not really that far aft (3 feet) from the COB, will this effect the balance significantly. How would I calculate the tilt in the waterline towards the stern using the above data.

Any information would be greatly appreciated.

Butch

[Ike]

The simple answer is no. It won't significantly affect your trim. It will be up at the bow and down a little at the stern but probably less than an inch. Without doing the calculations it's hard to say exactly how much. It will add a lot of weight to a 22 foot boat though and slow you down a bit. That's a lot of weight ot add ona 19 foot waterline.

[PAR]

Yep, your trim will be altered a bit, but not much.

Amigo is a fat, little cruiser. My numbers show she displaces 5,100 pounds with 1,775 in ballast, which provides a D/L of 327. At 5,500 pounds her D/L is 352. Both of these numbers suggests she's a heavy cruiser.

Some quick calculations indicate her vanishing point of positive stability is 122 degrees at 5,100 pounds and one degree less at 5,500, so you can see she's not affected much. This boat can easily handle a few well feed guys hanging out in the bilge (512 pounds) so don't be too concerned. Paint your boot stripe after sea trials, so it will appear to be just as if you planed it thus. Avoid the temptation of tossing some countering weight in the very ends of the boat. This is the worst place to do so and will decrease capasity further.

[ButchL]

Thanks for the information

[lazeyjack]

if you are able, put your load in and try balance the boat on a jack in her cradle, I have done this with big boats when pouring ballast,