Dimensioning of plywood cockpit floor

Deflection, allowable strength or both parameters?. This could be a more correct question. What do you think?.

 

Hi @gonzo .. my concern is about deflection.
I was asking me how much a panel of a specific size is allowed to deflect, that it still feels rigid when stepping on it.

 

It is very subjective. Is this for a production boat, so you are trying to find a consensus?

 

It has a subjective component, no doubt, but a technician must design with objective values that prevent excessive deflection, which would lead to premature fatigue and material collapse. The question, I would say, is, "What are those values?" No, I don't have the answer to that.

 

The way to determine the answer to the question is via testing.

For me to gutcheck, I must convert to known measures in English. So 26” x 11” is the panel. The effective span is thus the 11” dimension.

Using my familiarity with 6mm okume, I can tell you, I would not be comfortable stepping on 6mm okume spanning this section. I would anticipate the deflection to be very little under decent bonding to the edges, say 12mm cleats and epoxy, but it’d be easy to punch through it, or break it under a point load or say jumping onto it.

I would probably want 8mm plywood supported on the bottom with glass for same reasons.

My gutcheck would be to use 9-10mm plywood or to add a layer of glass to the bottom of the 8mm and calc the weight delta and choose the lighter.

I weigh 100k, so I would more likely use the 10mm or 9 and glass it..

To ~not~ feel any give; 12mm ply would be my choice.

 

Hi @fallguy
this is the kind of answer I was looking for. Thanks for sharing your practical insights and experiance.