Glen-L.com

I am repowering a Stiletto from 280 lb 85 HP 2 stroke to 370 lb 90 HP 4 stroke. The net gain in weight is 90 lbs. At rest this boat settles pretty low in the stern with the existing engine. To compensate for the added weight I am considering adding buoyancy chambers on either side of the transom, similar to a swim platform. These would consist of two roughly 18"x18"x6" foam filled pieces, naturally faired to the existing shapes, which would provide about 90-100 lbs buoyancy. Two concerns here:

1 - Is it better to follow the plane of the bottom all the way to the back of the proposed swim platform, or, come up a couple inches from the planing surface so it is only in the water at rest?

2 - Is the existing per spec transom stout enough to bolt these on or will they have to be bonded to the various adjacent hull surfaces?


Any thoughts you guys have would be appreciated. I wouldn't want to turn a boat that turns on a dime into one that turns cartwheels!!

Torque

Exactly what will happen if you do this, I don't know. If you extend level with the bottom, you are extending the planing surface and it must continue the plane of the bottom, with no radius on the aft edge. May be difficult to do; could raise them above the bottom, but this would decrease bouyancy value.

Total bouyancy represented by chambers will depend on how much submerged. Bouyancy is measured volume of water displaced, so anything above the waterline is only "potential" displacement.

Whether you have to beef up the transom would depend on how far aft they extend. It would probably be best to brace up to the transom.