It looks like you're new here. If you want to get involved, click one of these buttons!
You might want to practice with it,
understand volumes of expansions, the extreme forces,
and it sticks like hell to almost everything.
Read completely - top to bottom -
....... you missed a step in the rebuild .
You want to re-foam the under hull to max as I understand your question .
The step you should have done before fitting the new ply deck is install the bridging . This can be made of 3/4" runners (1x4 pressure treated is fine) .
The bridging simply does what it sounds like , it bridges across the beams . It should fit from side to side and spaced aprox. every 16" on center .
After the bridging is fastened to the beams , then you fill the hull with the 2 part expanding polyurethane closed cell foam . Just pour it in between the bridging and allow it to expand . Add a little more here and there as needed untill the intire hull bottom is filled and the foam expands through the bridging gaps .
Yep , it's now all bubbled up above the bridging 1x4's .
Next step ... simply take any hand saw and cut the foam flat off with the top off the bridging . Let your saw lay flat across the 1x4's as you cut off the over fill foam . Scrap off and/or sand off any foam that has stuck to the 1x4 tops as you feel needed to allow the new ply to lay down flat to the bridging .
See what I meant about missing a step . The ply you cut fits nicely to the side right now , but there will be a small gap when you raise it 3/4" .
So just for neat , clean and trim looking finish job ... choose some material to fit the inside corner between the ply and the hull sides . My 1st thoughts for a suggestion is some old garden hose , but other materials can accomplish that minor detail well also , so use your imagination on that one . Whatever material just be certain it's marine enviroment durable .
I've assumed you will be re-carpeting the deck , and it will finish out ok also if you just allow the carpet to fit snugly to the sides . There will be a dip at that gap the thickness of you ply . Don't concern that the ply won't have any support at the sides if it's not touching the hull sides , it shouldn't be touching in the 1st place but a small gap should be allowed . The foam between the bridges will support the ply . Also when you fit the bridges , allow a 1/8" gap at sides , don't fit them tight to hull sides ... same principle as the ply , close but not tight , not touching .
Do you understand what I have said Ok enough to go back and add the bridging now .
One other thing . The 2 part foam comes in differnt densities . 2 lb. foam is good for floatation but not any serious structural work . 4, 6, and 8 lb. foam are used for more structural work . The higher the number , the denser (harder) and heavier the foam . 2 lb. foam supplys 50-60 lbs. of bouyancy per cubic foot ... and so on .
I don't know what type ply you used . You should be using a "marine grade" ply . Fir marine grade is the least expensive , and it works and holds up just as well as the expensive stuff like Okume or Mahongany , etc. . If you used regular exterior Yellow Pine sheathing grade , it will self destruct in a couple years . If it's an interior grade ply , it will rot and delaminate over night .
Decent little fishing rig you got there , does the job fine doesn't it ... worth fixing up for sure .
Oh , almost forgot ... allow the foam to not only puff up and feel dry to your touch , but allow a couple more days before cutting ... it needs to finish expanding and fully cure (takes a few days) .