What's the strongest "coring" material for hatches
 

Re-coring my 20SF hatches and want the strongest material in particular for the longer hatch because my kids are animals and like to party!!!!:):):)

Just curious what everyone's opinions are regarding strength. Weight is a non issue....I like heavy hatches/lids and any weight forward wont hurt to bad.

Plywood...

Not as heavy as plywood but Bluewater 26 is some strong Coosa.

Now now, Sailors have made concrete float.

Really fond of hydraulic cement ! No shrinkage !! With rebar of course.....

There is a bridge in Stuart.

Haha, concrete. I have a friend who built sailboats here and swore up and down that concrete makes the best sailboats. Hard to believe, but he showed me photos.

I just recored Some decks and made some hatches for mine. I used 1/2” Finnish birch plywood. You can get it from a wood store not Home Depot or Lowe’s. The Finnish just means (more or less) that you have a substantially higher number of plys vs traditional plywood. I’m very pleased with the results of it, so far.

11 ply’s I believe on this one For around $50-60 for a 1/2” 4’x8’ sheet

https://i.postimg.cc/wtk1H034/075-A4...8-DACA92-B.jpg

The teak 3/4” 4’x8’ at $280 was only 7 plys. The maple 3/4” was 7 plys as well at $110/ sheet. That’s prefinished cabinet grade plywood. You’ll find the big box stores are even lower counts.

Thermolite (coosa) would work well too. It’s lighter, water resistant, and bugs won’t eat it. End grain balsa may be a good choice for lightness (Over plywood) but doubt you will notice a difference In sturdiness.

Good luck!

I like core cell but it's $$

strick

:D:D:D:D touche' LOL!!!!

Thanks all........I just want zero flex on the big hatch because as I stated, my kids will inevitably test my coring skills. I was thinking wood or coosa. I'm using coosa on the deck.

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

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.

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)

Great info guys!

Effects of Increasing Core Thickness
 

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.

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.