AA Blackjack Floor Repairs

[Dennis P.]

I would not use coosa board for stringers. I don't believe it's modulus of rupture comes anywhere close to that of wood. I believe wood sealed and glassed properly will be just fine in this situation.

yes, i agree to a point. you can't just compare the physical properties number for number.

the overall strength and stiffness of the wood stringer is its cross section alone.

with a composite member, you have to take into account the relative stiffnesses of the materials. so for example, a stringer made up of a foam core and wrapped in fiberglass cloth and epoxy resin, 99.5% of the strength and stiffness is the FRP shell. The foam just goes along for the ride.
With a wood or coosa type material, it is more like 80/20 or 90/10 type ratio.

concrete and steel reinforcing has a modulus ration of about 10.

The only benefit I see to coosa is the inheret no-rot and dimesional stability of the material.

I am also toying with making my own stringers by using blue/pink foam as a core and laminating it myself, vaccum bagging my making a 'bag' out of polyethelene sheeting.

as always, work gets in the way of play

 

[Eric Patterson]

Dennis

I would pursue making my own just out of fun for the discovery process. I think there are many ways to go and end up with a satisfactory result. I just wouldn't discount wood in favor of Coosa for some perceived superiority because I don't know that one exists and wood is so widely available, cheap, and proven if properly encased in glass and epoxy.

 

[greg setter]

I'm going to get this going again because I am in the middle of the same thing. Difference is, there is only one stringer in my blackjack, which is a phoenix pokeboat build. I also have a well in the back of the deck at the stern where there is a drain hole. While I don't have a photo of the section in front, the floor deck ends just underneath the bow deck and there is small depression there for the contour of the hull after the floor deck ends and a hole in that. It drains to the hole in the well. But what I didn't realize was that there is no tube that drains it, it just goes under the deck. So that is why the stringer rotted and why the foam was water logged and why the plywood floor rotted. I'm not sure why they would have made a tubular section adjacent to the stringer, you certainly didn't need it since there wasn't a tube in it. I didn't figure that all out until I had cut away the glass on the top and the open side of the stringer so I could kind of peel the glass off and save it.
This picture is taken looking forward and you can see the tube shape if you zoom in.

This next picture is taken from the side and on the right you can see the well near the stern. You can also see there are not two other stringers. The floor deck was glassed to the sides of the hull.


At this point I think I will just close off the drain holes front and rear,I don't want water flowing underneath the floor. I'll fill the void with life jacket foam, and just keep a sponge in the bow for the little depression that could catch a little water if it got up there. I'm also going to cut that tubular section out as it serves no purpose. I will take a picture of that area tomorrow to show the depression in front of the floor. I don't think keeping the current set up makes sense as it will just start rotting the stringer again.