Building foam sheets over MDF frames. Best way to secure?

[mrybas]

Hi,
I’m building a 14’ catamaran dingy out of Divinycell H80. What is the best way to secure the foam sheets onto the MDF frames while laminating the exterior of the boat? Stainless brads? plastic screws?

 

[gonzo]

Trim screws work well. You can pull them through the foam after the exterior is laminated.

 

[Mr Efficiency]

Normally you'd have longitudinal battens over your frames, and the foam screwed to that, from beneath.

 

[fallguy]

Typically, you would cleat the foam from underneath.

But you can also use a wood screw and a flat wood washer about 2" square.

MDF will require predrilling or it will shatter.

For my build in a female jig, I used screws into battens running for and aft; sadly had to penetrate the laminated panels. I wasn't crafty enough to create a method that didn't. However, some of my panels were held in tape seams and this s much preferred. Same for you when it works....

 

[fallguy]

Also, for your hard chine design, you can just screw; then glue the seams; then remove the screws. The boat should hold the shape pretty well at that point or you have erred.

If you had a trouble spot; you can also hot glue the foam to the jig temporarily.

I used hotglue a lot in my foam build as a temp hold.

 

[Chuck Losness]

Take strands from woven roving and tie the foam to the mold. After glassing the exterior all you have to do is cut the strands to remove the hull from the mold. As suggested above it would be best to have ribbons to tie the foam to.

Have fun with you project.

 

[wet feet]

If thats the extent of your support structure,you have an unpleasant surprise ahead.Ordinarily I would expect some definition of the stem(s) and sheer and a liberal covering of battens.You can sew or tie the foam to any part of the framework and you need to take some care to make the joints between sections of foam fair.

 

[waikikin]

Fishing line or back screw. Might be worth pre laminating sheets and leave one skin off near the bow.
Jeff

 

[fallguy]

If thats the extent of your support structure,you have an unpleasant surprise ahead.Ordinarily I would expect some definition of the stem(s) and sheer and a liberal covering of battens.You can sew or tie the foam to any part of the framework and you need to take some care to make the joints between sections of foam fair.

A fair assessment. There needs to be a minimum of a batten at the gunwhale.

 

[mrybas]

I got a chance to dry fit the pieces to the frames today. They fit pretty well except where there’s a lot of direction change close to the bows. I’m thinking about drilling small holes and dry stitching with leftover carbon scraps to pull the panels together (or maybe small zip ties)?

Next step is to bog the joints, sand joints, then tape.

 

[fallguy]

Looking good.