rear floor access panel

I have a 75 SN. I need to replace the floor center section behind the motor box. does anyone have the dimensions of this piece? what is the best material and thickness for that section? Thanks

Yes, what Pete said. My '81 SN's rear section is 3/4 x 34 1/2 x 39, 7 ply marine, but I believe each section is made specifically for the boat it is in. The number and thickness of glass laminations (or no glass laminations) on the top and bottom sides will change the overall height of the panel and may make it lower or higher then the adjoining sole (floor) of the boat. You also need to consider the edge glass wrapping, or/and thickened epoxy and perhaps carpet in some cases depending on your preference.

I assume you are asking because you lost the original and can't measure it?

I've replaced two of those pieces for friends of mine. All it takes is a 200 lb. plus person to step directly behind the motor box on one foot and crack it. What I have done is mount a 2x4 perpendicular on the bottom of the plywood that reaches each stringer. Cut a half moon out for the drive shaft clearance and you won't have any flex.

I have been using this from Menards it's approx 1/4" with 5 plys. I cpes it and doubled it up using Cabosil and epoxy. I have to replace two hatches on the Shamrock which delaminated due to the way screws attaching the hinge were installed. I plan to do that in the summer the same way.

Here's a Mustang 17 I did a couple of years ago. You can see the line of screws on either side of the inspection plate hole. That's where I put 2x4 braces on the backside.

SWANY wrote: The braces are a great addition for sure. But I would run the grain of the plywood the opposite direction. Especially with where the inspection hole is located.

Joel,
Great point. I suggest the same since if a non marine ply is used and if there is a void in the center veneer, the strength won't be affected in the port to starboard direction.

I'm glad the topic has come up, I need to do mine this winter. Although I'm not completely impressed with marine grade from either Menards or Owl lumber I just don't think I could put today's treated plywood in a boat. Such a lower quality than say 10-15 years ago, at least not without braces like Tim did. I would be worried About it warping even still.

It doesn't matter which way the grain is going with a piece of plywood that small with braces on the bottom. And for "drying out and warping" is bull. I replaced mine in 1998, no warping at all. I put 7-9 coats of polyurethane on the top side and edges like the one pictured above.

So you think all the interior layers run the same direction as the outer veneers?

I'm not confused. I know that a piece of plywood would be useless if every layer had the grain in the same direction. It would bow very bad. I know a little about plywood, my Dad retired from GP. But back to the original statement, the small piece behind the box, with braces on the bottom side, grain direction is not an issue.

Tim agrees with Tim.

Wow Swany, you were 4 years old when I bought my Mustang. You got smart quick in your short time on earth. Comparing sub-flooring to this piece of wood behind the dog box is wrong.

This talk about wood and anal-igy's is getting too heated.

Joel, the D in Tim stands for Dikhead, don't mind him he tends to be an azz on here. Thanks for your qualified input!!

BTW, when I was at my sis's place at Thanksgiving I found that new bridge at Red Gate rd on my way home, would be perfect for a BF flyer, LOL

Ok, thread jack off

Thanks Queerner, I had a bet going you would show up when anal came up.