1st time coosa board user

[martin]

Originally Posted by Jeff79Sceptre

Unfortunately, I only used it on one side. I really just mimicked the factory layup with the exception of the plywood. I figured I couldn't tab it underneath so why waste the epoxy and mat since there is really no weight in the center of the fuel tank. Most of the weight is closest to the stingers. I'll add some more 1708-6" toward the center from the stingers to help out. I did have Sunshine to weld some tabs for the new tank to keep from laterally moving but I know the will not help from vertical compression from slapping on waves. I can walk on the tank bed now but 800lbs of fuel may crush my layup method.

Yea Jeff that makes sense now. This coosa board , does it have roving glass inbedded in the foam.. if so I would recommend redoing your floor. 20lb desity will flex and crush over time. without the one side being laminated.. and when that happens the glass will fail on the tank side..I would cut out your board and glass the other side then cabosil epoxy it down then tab it in.. Also the glass that is not sealed will wick up moisture and fail..... I was told that you could just do one side as well. but it just made no sense to me ...Sorry for the bad news But this is one of the most important decks in the boat. this is just MHO. and you dont want your tank being supported by screws and alum tabs...or have to cut out your deck to do all over again...

[Jeff79Sceptre]

Martin, thanks for your help. I did coat the coosa with epoxy I just didn't use mat. No, big deal on cutting it out just one more skillsaw blade in the graveyard. I'll put 2 layers on it and then cabosil it back in place. Now, I just need some warmer weather.

[Blue_Heron]

Originally Posted by Jeff79Sceptre

Unfortunately, I only used it on one side. I really just mimicked the factory layup with the exception of the plywood...

Here's a good article on cored laminate (sandwich panel) construction:

http://www.boatdesign.net/articles/foam-core/index.htm

It's a little technical, but you can skip over the formulas and still get the gist of how a cored laminate works.

A cored laminate's strength is all about the laminate, and only a little bit about the core material. The thickness of the core has a greater effect on panel stiffness than the material the core is made from. And it only works if there's laminate on both sides. When you subject the panel to bending loads, one side is in compression while the other is in tension. If one side is missing, the core has to absorb the load and will tend to deform, allowing the panel to bend.

Hope this helps.

Dave

[Jeff79Sceptre]

Well, I cut the coosa out and put 2 layers on the bottom for a total of 4 layers.2 on top and 2 on the bottom. Now it's super strong. It does weigh more than I expected but way less than 3/4 plywood. I cabosilled it back in place and have a heater on it now to help the cure. The temps keep dipping into the 40's and highs of 65 or so. It's holding the new fuel tank from getting installed.

[martin]

Originally Posted by Jeff79Sceptre

Well, I cut the coosa out and put 2 layers on the bottom for a total of 4 layers.2 on top and 2 on the bottom. Now it's super strong. It does weigh more than I expected but way less than 3/4 plywood. I cabosilled it back in place and have a heater on it now to help the cure. The temps keep dipping into the 40's and highs of 65 or so. It's holding the new fuel tank from getting installed.

Good to hear that.. I just pulled the 3/4 ply fuel tank bed out yesterday. It had roving and mat on one side. ANd nothing on the bottom side. This was original.. I just cant believe that was satisfactory in the 70 s