What Core Material would You Use?

[sgharford]

Captdis - I tried searching for your article and could not find it. I am very interested in reading it. I'm still leaning towards plywood. That 6x12 unsupported section I made mention of in first post is just as much concern as bow pulpit area for strength. I like the idea of layering the 1/4 plywood in staggered pieces to cover seams so that it is effectively one giant piece. Any seam in that 6x12 unsupported area is a weak point. Many times I’ll have 5 to 10 adults standing in this area. I could use 1/4 coosa in similar fashion, but I think I'm getting allot more bang for the buck with plywood. I have great respect for BoatsB advice and fact he has done it for 20 years with great success also helps mitigate any possible water intrusion worries. I'll treat install like balsa and over drill out all holes thru deck and fill with epoxy, just like balsa install.

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.

[Pascal]

I would use Divinycel... This stuff is really good and that s what Hatteras has been using for a while now, isn't it? Light, very stiff, closed cell, easy to use and extremely strong

I m using it for the frames, deck, stringers of the 26' classic sloop I m building, great material

[bigbill]

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.[/QUOTE]

how did that work for you. if this was true, you would only have a bad spot about 4x4..
i know it didn't work on my boat

[sgharford]

Mine completely delaminated from the skin so all the squares were sitting in a puddle. I threw in there as an interesting tib bit I thought I'd pass along. I thought all the squares where there because it was made from scraps of balsa and it was cheaper, like particle board.

[Boatsb]

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.

how did that work for you. if this was true, you would only have a bad spot about 4x4..
i know it didn't work on my boat[/QUOTE]

Balsa is great stuff for certain uses. the strength to weight ratio is incredible. I built a model bridge span using balsa and held hundreds of pounds with this 4.5 oz structure.

The issue is the end grain is a wick for moisture. even if it does not carry to the next cube through its side contact the water will break the bond at the bottom and travel at the skin to the next piece.

Closed cell foam is better in the fact that it will not absorb moisture but it will also lose the bond if left in water long enough.

Now think about the strength of plywood as compared to a similar dimensioned piece of solid wood.Plywood is stronger and more flexible. laminate the curved crown of the deck with multiple layers of the plywood and you have a strong deck. laminate them with a resin ( poly or epoxy) and you have an almost waterproof strong deck especially if you add in the mat between layers.


Its the same idea as the Glu Lam beams used in construction of houses and buildings.

[sgharford]

Balsa is great stuff for certain uses. the strength to weight ratio is incredible. I built a model bridge span using balsa and held hundreds of pounds with this 4.5 oz structure.

I did that project too when I was working on my BS in Mechanical Engineering! We scarfed the joints, should have used glue - ours only held about 80 lbs.

[Avenger]

And here I always thought they were cut into squares so the core could conform to the shape of the deck or hull. Whoda thunk?

BTW, my earlier suggestion on the solid glass was only meant for the pulpit/windlass area since that's what everybody was focusing on. Doing the entire repair that way would be a bit too much even for my style of overdoing things. It was clear in my head, but not in my post. Sorry.

[Boatsb]

I did that project too when I was working on my BS in Mechanical Engineering! We scarfed the joints, should have used glue - ours only held about 80 lbs.

I did it in 11th Grade AP physics class. had a great teacher that really motivated us to learn more about anything that interested us. The let him go before he had tenure because they had a bunch of olf fat stupid women who were not very interested in teaching afraid he would become their boss and make them work.

[captddis]

Captdis - I tried searching for your article and could not find it. I am very interested in reading it. I'm still leaning towards plywood. That 6x12 unsupported section I made mention of in first post is just as much concern as bow pulpit area for strength. I like the idea of layering the 1/4 plywood in staggered pieces to cover seams so that it is effectively one giant piece. Any seam in that 6x12 unsupported area is a weak point. Many times I’ll have 5 to 10 adults standing in this area. I could use 1/4 coosa in similar fashion, but I think I'm getting allot more bang for the buck with plywood. I have great respect for BoatsB advice and fact he has done it for 20 years with great success also helps mitigate any possible water intrusion worries. I'll treat install like balsa and over drill out all holes thru deck and fill with epoxy, just like balsa install.

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.

I will try to find it or I will redo it. I did use epoxy saturated plywood under the windlass and pulpit.
Used all epoxy on the repairs. It was amazing how much stronger the epoxy is.

[Ernie Piotrowski]

I would give Nidacore a try. Replaced the cockpit on the 32 flybridge when the circular hatches leaked and left the core a pile of mush. The product is a honeycomb design made in thinknesses of 1/2 to 6+. Mine is a SCUBA charter boat with the cockpit holding 24 tanks, weight belts, gear bags and 8 persons. My son tried to dent the circular hatch cutout with a 16oz claw hamme(claw end) and couldn't even dent it. There are a couple of offshore CC mfg using the material. I wouldn't use anything else if future repairs in other areas become necessary. Total weight on the cockpit it approx 2500-3500 lbs. No flex and no water intrusion/migration worries. Google the item and they will be happy to send you info and a sample. Good luck with your repair.