Not specific to your issue of strength, but I glued a 2x4 to the top of my section #4, in order to make it wider, and more comfortable as a masik. This also made the top of the form stronger, but not the sides or bottom. If you did this, I would recommend radiusing the back bottom edge aggressively, with a plane or rasp or something. I radiused mine with a sander, figuring I'd knock the hard edge off, and I'm still able to get in an out of the boat, and able to slide a hand flat between my knees and the bottom of the masik. However, a friend of mine can't get into the boat. He suggested the greater radius, because it would give just that little extra 1/8 or 1/4 inch for kneecaps to fit in behind and under the masik. Take a look at some pictures of masiks from the qajaqusa.org forum.

Also, for sections #5 and #6, I made the tops of the forms extra thick, I believe 1.5" instead of .5", figuring my deck beams would need additional support for when I sit to get in and out of the kayak. On a Sea Rider, the problem is that the hole in the form to store stuff immediately behind the coaming is too small to fit a Nalgene bottle. I now use very small dry bags, and cut up my apples and oranges when putting them into my lunch drybag. Oh, how annoyed I get trying to pull that bag out when a full apple gets stuck...

I have not encountered problems with the bottom of section #4. I sit with 1/2" minicel foam pieces cut to fit snugly between the chine and keel stringers, and sections 4 and 5, then put a 3/4 length Thermarest z shaped foamy pad on top of that. My legs are pretty straight out in front of me, but maybe just bent enough at the knees so that the bottom of section 4 is hardly noticeable.

To get more room in section 4, you could build it up a smidge higher, keeping the positions of gunwales the same. This might affect the weathercocking trim a little bit.

On my next one, I will modify the shape of the top of section 4, because the smooth arc doesn't work well for me with forward finishing rolls. I'd like to have a masik with a flatter underside, to lock my knees from slipping toward the centerline. I have considered reducing the top of the arc with a piece of glued in minicell, shaped to be flat across the bottom, but then I'm afraid it would be a little more difficult to get in to the boat. I've also considered increasing that radius, possibly with a drum sander attachment to a drill, maybe a Sureform. Eh. Or I just keep paddling it and having fun.

Brian

: I am looking for a way to make a smaller plywood frame in a Yost style boat.
: I want to thin down the frame at the front of the cockpit but still
: maintain adequate strength. I made a mistake and cut one thin and broke it
: on another boat, so I know that there is a lot of force on these two when
: you get in and out of the boat.

: I am loosing a lot of 'knee room' under the cockpit and I am find that the
: frame is a bit tall under my legs too. I hate to make the cockpit longer
: and would prefer to just make the opening in the frame larger. So I have
: been thinking about ways to "thin' the frame.

: The simplest idea I can come up with is make the fame thicker, therefore
: stronger. Maybe make two identical frames and glue them together as one.

: Another idea is cut the frame off at the top stringer and then build a masik
: for the cockpit support out of wider solid wood. That would take up less
: space. But I would still have the issue of the frame in the back of my
: legs, but that is less of an issue.

: I tossed around the idea of plywood laminated (the flat way) frame but the
: bends would be hard to shape. the bends at the chines would just be to
: sharp.

: So, anyone have any other ideas I have not thought of? Making a thinner
: double thick frame seems like the best idea.