aluminum hull wobbly after removing foam

[martinmariner]

I have a '67 18' aluminum mirro craft out of which I removed the old rotted plywood floor and the SOAKED foam underneath. I rebuilt the floor using aluminum T-bar spanning the hull and resting on each chine with mdo plywood on top. (Tried to attach T-bar to chines using 3m 4200 with limited success.) Anyhow, now because I did not really want to replace the foam because of weight/draining issues, I have a hull that moves quite a bit because of nonexistent stiffening from the previous foam or any aluminum from the original manufacturing of the boat. (if that makes sense.) Do I have to replace the foam or does someone have an idea of how to stiffen the bottom of the boat so it does not move while underway.
Sincere thanks,
Martin

 

[Mark42]

Re: aluminum hull wobbly after removing foam

People often think that foam is just there to keep the boat afloat. The fact is that foam often provides stiffening, rigidity and sound deadening.

If possable, I would pick up some 4 lb foam and pour it in. New polyurathane foams do not break down with extended water contact like the old polyester foams did. Polyurathane foam is what floating docks are made from. 4 lb foam is more structural than the usual 2 lb foam. So if you want to add more rigidity and some strength to the hull, buy the 4 lb foam.

 

[Bondo]

Re: aluminum hull wobbly after removing foam

I rebuilt the floor using aluminum T-bar spanning the hull and resting on each chine with mdo plywood on top. (Tried to attach T-bar to chines using 3m 4200 with limited success.)

Ayuh,....

It ain't the Foam,.....

You took all the structure out of the hull,+ Replaced it with Bubblegum......

 

[Bob_VT]

Re: aluminum hull wobbly after removing foam

You would be better using aluminum pop rivets, or bolts, or even west system epoxy which will not give when secured.

 

[Mark42]

Re: aluminum hull wobbly after removing foam

Ayuh,....

It ain't the Foam,.....

You took all the structure out of the hull,+ Replaced it with Bubblegum......

Oh, my. I missed that. All that is holding the cross braces in place is glue?

Time to remove it all and start over. Attach the braces with aluminum nuts and bolts or rivets.

Foam will add a significant amount of rigidity, even if the cross braces are not properly installed.

 

[martinmariner]

Re: aluminum hull wobbly after removing foam

O.K. guys, let me try to explain. The old plywood deck was resting on the old saturated foam with no attachments to the hull, chines or anything. The new aluminum T-bar is only to support the deck and was never meant by me to provide rigidity or structural integrity to the hull whatsoever. The 4200 was an attempt to somewhat secure the new deck to the boat itself so that I could avoid thru-hull fasteners. It is actually holding nicely and the T-bars or decking does not move. I appreciate the word on the 4 and 2 lb. foam and would love any more info. on those. (Best place to purchase without ordering on-line. I live in Portland, OR.)
Again, my sincere thanks for your time and expertise.
-Martin

 

[cordell]

Re: aluminum hull wobbly after removing foam

http://www.uscomposites.com/foam.html


cordell