Hatch core material?

[SBD]

I have one large hatch that covers my fuel tank (39x39) and it is a little squishy. I thought while I have everything torn apart I should re-core it. What should I use keeping in mind I live in a rural area and have limited sources for material.

Thanks!

[Bigshrimpin]

4" x 4" x 1/2" inch plywood squares work great!!

[aldo]

Nida-Core comes in 2'x4' sheets(ships easily) and is strong & light weight. Can't tell you how happy I was with the result on my floor.

[SBD]

Plywood is certainly cheap and available, anyone ever use blue foam?

[Blue_Heron]

...anyone ever use blue foam?

Sean,
I have, but I wouldn't use it for something structural like a deck hatch. Polystyrene is susceptible to attack from all sorts of solvents, including gasoline, motor oil, and polyester resin. It also has pretty low shear strength which is what you need in the core of a cored laminate. A large person on top of that hatch when you're in a heavy sea could cause a styrofoam core to fail.

All that being said, if you can protect the core from solvents, and you make it thick enough that the shear forces are low (say 1.5" thick), it could work. I just don't think the weight and cost savings are enough to make it practical. I would go with plywood blocks like Bigshrimpin suggested, but for a hatch that big, I would go with 3/4"

Dave

[SBD]

All we have here are heavy seas so looks like I'll skip any desire to experiment. Good to know thanks a bunch!

[shine]

[blue insulation foam will delmaniate. Its does not have the peel of sheer strength needed as a core in a composite sandwich. Its fine for non-structural insulation assuming you use a resin that will not melt it.

plywood, foma core, honey comb, balsa, lots of good and proven options out there.

[workinpr0gress]

I'd just use plywood myself, people get stuck on the grade. Skip poly resin IMO. If the epoxy resin is thin enough and you make sure it doesn't kick off to quick it'll really soak into the wood nicely. Worked/ fished on more than a few 30yo cold molded customs that have never had a major issue while pulling ridiculous duty and hours on run of the mill plywood.

[SBD]

Keep in mind this is made out of blue foam, its not as feeble as you might want to believe...




Unfortunately I can't even get it around here, os I will go with the proven and available. I have a good stash of epoxy, so I am going to go ply/epoxy. Thanks for all of the advise...I love this site!

[Blue_Heron]

[blue insulation foam will delmaniate. Its does not have the peel of sheer strength needed as a core in a composite sandwich. Its fine for non-structural insulation assuming you use a resin that will not melt it.

I'm going to qualify my earlier post. While I still wouldn't recommend it for your application, Sean, there are times when the blue foam might be used. Shine is right that the peel and shear strength of blue polystyrene is very low compared to other core materials. But you can compensate for the low strength by using a thicker core.

The core in a composite sandwich subjected to bending loads, whether it's plywood, foam, or some other material, acts like the web in an I beam and resists shear forces. The laminate on both faces of the panel act like the flanges of an I beam and resist compressive and tensile forces. Like an I beam, the farther apart the flanges or laminate surfaces are, the lower the forces acting on the materials. Bottom line, if the core is thick enough, it doesn't have to be as strong to resist the same bending loads as the core in a thinner sandwich laminate.

So one application where it might make sense to use a blue foam core is for the deck over a cooler where you want a thick core for thermal insulation anyway. I've built an in-deck cooler and intend to core the lid with blue foam about 1.5" thick. The lid will only be about 15" in the short dimension, so bending loads will be very low.

Dave