Floor Joint Design?

[76SeaRay]

I am almost to the point where the floor will go on the new stringers. I have a question on the point at which a floor joint is required (8ft plywood in a 22ft boat) at right angles to the stringers. I am thinking that I should bevel the edges between the two pieces at 45 degrees with thickened resin in the joint where they meet. I am also thinking I should add a backing board along the seam or even another bulkhead underneath the joints. What are the thoughts on the way to handle this?

Thanks....

 

[jbcurt00]

Should ask this in a project topic, prevents duplication of posts and pix

 

[76SeaRay]

Sorry, I thought this would be a generic design question that applies to any project as opposed to specifically for my project and would be easier for others to find with the subject line specific to the general design question.

Thanks.

 

[Bondo]

Sorry, I thought this would be a generic design question that applies to any project as opposed to specifically for my project and would be easier for others to find with the subject line specific to the general design question.

Thanks.

Ayuh,..... In the last video in this thread, you can see how f'n does his joints,....

 

[Chris1956]

You are going to cover the plywood with glass and resin right. That adds lots of strength, Are you installing foam under the deck? if not, why not?

If you are using 1/2" plywood, foam and glass/resin, no joint reinforcement is necessary

 

[76SeaRay]

Yes, using 1/2 inch marine plywood, coated on the bottom side with resin, covered on the top side with resin and glass. I will be filling with foam.

 

[todhunter]

I just butted my two pieces of plywood together. Pre-covered bottom surface with 1 layer of CSM. Resin soaked edges. After installation, top surface got 1 layer of 1708 and 1 layer of CSM. I did locate the joint between the plywood over a bulkhead.

 

[GSPLures]

I did as stated above also. When I filled my screw holes and the pour holes for my foam with PB I pushed some in between the joints. I used a bondo spreader to go a few inches past the joint on each side to fill in any minor difference between the 2 pieces. I just used the left overs from the mixes I used for the fillets.

 

[jbcurt00]

Yes, using 1/2 inch marine plywood, coated on the bottom side with resin, covered on the top side with resin and glass. I will be filling with foam.

There is no generic 'resin', epoxy, polyester or vinylester.

Polyester resin is better used WITH fiberglass then w/out

 

[JASinIL2006]

Are your joints going to be above a stringer/bulkhead or will they be floating?

If the joint is not supported by structure below, at the very least, I'd have a plywood cleat that runs below the seam to which both decking boards are screwed. I'd want the cleat to overlap the seam on both sides by at least 3".

 

[76SeaRay]

I was thinking of using only polyester resin on the underside as a wood sealant since it wouldn't be in pooling water in the case of a leak. But, as a second thought, if water did get under the floor then the floatation foam could trap water against the underside of the flooring which only resin might not be enough. I will go with a layer of CSM on the underside. I will likely end up with 3 to 4 times the amount of resin and fiberglass originally installed at the factory.

As to the joints, I will be supporting them from underneath at the joint with a rib/bulkhead or cleat. I will probably bevel them on a 45 degree angle just as added strength. I just replaced a floor joint in my fifth wheel where I didn't have a butt joint supported from underneath so learned my lesson on that one. The floor flexed at that point. My original boat decking did not run from side to side as one piece but had a 26 inch x 76 inch piece over the center belly fuel tank supported by aluminum cleats to the stringers on the sides running along the length of the tank and butt jointed to the deck plywood on the sides. It was fiberglassed over so not removeable. Not sure yet if I will use that same approach for joints for the "non-removeable tank cover". It is an aluminum tank and had foam between that floor piece and the top of the tank. to support the floor.

 

[JASinIL2006]

If you have a decent cleat beneath the seam, I doubt a 45 degree joint will make much of a difference, but it cannot hurt.

Glassing the underside is a good idea. Resin by itself will just crack if there is any flex at all, and that would pretty much defeat the purpose.

 

[GSPLures]

If you put flotation foam under the floor that should support the joint. When you tab in the edges run a strip across the joints then glass the deck. Should be more than adequate for a butt joint