bertram31.com

The engine boxes on Crows Nest were lengthened by about 9" to accomodate the Detroit 8.2s. Whoever did it added f'glass stiffeners to the inside of the boxes. It also looks like they added 1/2" of styrofoam coring to the boxes, and glassed that in with a layer of cloth. I took out the foam/glass stuff on the aft vertical panel of the port box because it was all delaminated from the box, and the box was pretty wobbly back there when you raised it. I glassed in 1/2" marine ply back there, and the box stiffened up a lot.

I don't remember my other B31's boxes being cored, and certainly not with foam. Were the stock boxes cored? If so, with what? The styrofoam stuff these are cored with is old and dryed out and doesn't seem to do much, if anything.

I'll probably take all the coring out eventually. Do the boxes need to be cored with something? If so, what?

Thanks.

John,

Bertram did add some coring to the boxes, if you could call a "core"... They used a 1/2" material that I suspect was the old version of Homasote and it was very sensitive to moisture absorbtion. It was just Bondo'ed on and a single layer of mat was overlaid. After the moisture set in, the boxes would weigh a ton and have very little rigidity.

I've replaced several, using structural pvc foam, (Divinycell), properly bedded and glassed over. Another suitable material would be Coosa/Penske board.

Here's one of Jim Bailey's engine boxes ready for fiberglass. This was done with 3/4" Airex foam. The stiffeners were made by cutting strips of Airex 3/4"x1 1/2"...

CaptPatrick wrote:John,

It was just Bondo'ed on and a single layer of mat was overlaid. After the moisture set in, the boxes would weigh a ton and have very little rigidity.

That about covers it. I don't remember it on my 1969 Anna E., but this 1977 Crows Nest is pretty much what you describe. Could I use marine ply rather than Coosa?

Thanks

Yup, plywood will work, but weight will be a factor...

No need to get expensive marine ply for this application. Use 2 sheets of commercial B/C ply that are 1/2 the thickness you want and laminate them together, opposing the warp with the C faces bonded together. Use a good quality wood glue, such as Titebond II Premium Wood Glue and work the sheets over a good flat surface, like your garage floor or driveway.

Roll the glue onto both surfaces to be bonded, lay the first sheet down and center the second sheet over it first. If you have a pneumatic stapler, you can work from one end to the other or use weights, (cinder blocks, old batteries, sand bags, etc). Allow the glue to set overnight before cutting your panels to fit.

Thanks. At this point, I'm just asking. I have enough to finish up this winter.