What's the strongest "coring" material for hatches

[dirtwheelsfl]

Its more about how thick the core is than what the core is. Can always put some “stringers” on the bottom side too...

[DAYTRIP]

I core everything hatch wise with airex t92.100. Primarily because it is easy to work with and has good properties. The core, with the exception of plywood offers very little in terms of added structure. Dirtwheelsfl said it, the thickness is a driver with any cored structure. If the thickness of the core doubles (and the skins stay the same) the strength goes up 4 times as much. If it triples in thickness it goes up 9 times as much. The key is adhesion to the core to get the most out of it.

[FLexpat]

Dirtwheels and Daytrip are both right on.
The original hatch cores on my 23 were 3/8" thick, ~4x4 plywood squares. Unfortunately the lower skin was just tied to the vertical edges of the hatch; pretty much no adhesion area, so when it was loaded it just ripped the lower glass off the thin little edge... All the original hatches sagged like wet blankets.

For the new ones I used 3/4" Corecell and tapered the edges of the core so that the lower skin ties to the upper skin for about 1.5" inside of the vertical part of the hatch edge. Did vac infusion with overkill layup and still lighter than original. Super stiff/strong. (If I find a good pic I will edit this post since my description probably sucks to read and follow)

[Thepistonhead]

Great info guys!

[Capt Terry]

Originally Posted by DAYTRIP

If the thickness of the core doubles (and the skins stay the same) the strength goes up 4 times as much. If it triples in thickness it goes up 9 times as much. The key is adhesion to the core to get the most out of it.

Daytrip- You are on the right track, but the benefit of increasing the thickness of the core is even more dramatic than that. For a given material and load on that material the thing affecting deflection is the stiffness of the structure, Moment of inertia is the engineering term for describing the stiffness of a structure. For a rectangular shape like the cross section of the hatch or core, there is a cubic term on the thickness, not a square term.

Moment of Inertia = [(base) x (height or thickness)3 ] divided by 12
Where is the 3 is a cubic exponent

If the core thickness is doubled, the Moment of Inertia is 2 x 2 x 2 = 8 times greater.

If the core thickness is tripled, the Moment of Inertia is 3 x 3 x 3 = 27 times greater.

So increasing the thickness is a powerful tool. Adding ribs can accomplish the same effect but with less weight.

[DAYTRIP]

Hey Capt.,

I was describing (intending to) strength (section modulus) vs stiffness (movement of inertia) . Both tell the story clearly though, make your core thicker and it gets stiff and strong.