seat framing?

[JeffM]

I've finished my CS20's tank sides and have been looking at framing the seats. I don't see any framing in the plans, but I'm leery of plumping my 200+ lbs down on nothing by quarter-inch ply (grain transverse or not) with nothin' underneath. I've installed 1X2 framing for the 4 So-Pac hatches I plan to install -- maybe that'll be enough since they're at some of the widest parts of the seats, but I'm not sure. Ideas?

Thanks, as always! I couldn't do this with any confidence withoug the support I get from you folks.

Most Important Lesson of December: If you MUST epoxy, use a heater! It takes about 3 times more epoxy to cover a cold surface than a warm one -- and then it slooowwwwly runs all the hell over the place!

[Joe Nelson CS#35]

I am in the same boat as you, but worse...bout 275. I doubled the thickness of all the seat tops. In retrospect, I think that going to 9mm would have been sufficient. I think that adding thickness to the seat tops was the easiest way to deal with our concern.

[mustangermatt]

I added transverse frames rather than change the direction of the grain (I assume you are using fir and referring to Grahams suggestion).

I did stress tests on scraps of my plywood and found :

a) Standing on a seat/deck is more of a concern than sitting because the weight is not as well distributed.

About 14"-15" square was about as large an area as I was comfortable with being unsupported so that is where I put my 1x2 framing in seats and decks.

I weigh about 185lbs., so you may want to revisit my demensions. I just laid 1x2 sticks in a rectangle on the ground simulating the frame spacing, dropped a piece of 1/4" ply on them and stood in the middle. If it was very springy or made cracking noises the span was too much (for my confidance anyway). The extra framing was less than 8 lbs. of wood, but a lot more time consuming than Joe's solution. I had a picture of the seat frames in an old post:

http://www.messing-about.com/forum/viewtopic.php?t=2432

[Designer]

When designing the boat I was trying to create a camper-cruiser-dayboat that was tough enough to do the the job but keep the weight down for performance and man-handleing. CS 20 hull #1 was built with the standard deck and is still going strong without any problems. When I walk around on my CS17 deck and cockpit seats with my 165# I feel some flex and I try to avoid abusing it by not jumping on it and try to walk where it is better supported . I, personally, wouldn't change the deck construction scantlings, even if I could wave a wand and magically change it. If you feel that you would like to make the seat tops/ decks more rugged, then 9 mm ply or adding some stringers or beams under the seats can help.

[JeffM]

Thanks, all! I like Mustangermatt's stress testing -- wish I'd thought of it (and me a science teacher!)

I think I'll stay with my intuition: a few stringers where the seat top is widest and I might step/sit pretty hard, trust the design elsewhere.