You might look into using a piece of capped pvc pipe in lieu of the wood. You would get a better float to weight ratio.
I'm building with the tire tube option. I don't have a photo, unfortunately, but I'm pleased with the results. I'm using a snowmobile trailer tire tube, which is small in outer diameter but fairly large in volume. With the wood frame it weighs around 10 pounds, and provides about 100 pounds of flotation. I like the shape because it is less prone to catching on anything, gear, swimmers, docks, etc.
An innertube, unless very heavy weight, isn't going to be stable enough when you're trying to get in and out of the boat. Especially if you don't leave it as an intact ring. Think of how a pool noodle bends in the middle when you put weight on it and you'll start to envision the problem with an innertube. A PVC piece will have the rigidity you need to use it as an extra step when getting back in from the water and will be more than sufficient with flotation. You could make it even a 4 inch piece of PVC but that would start to interfere with paddle clearance when not deployed, I think.
Not cutting the tube, using the whole ring.
(This all assumes you mean to get into the boat from the outrigger side- using it like a ladder- rather than using the stirrup on the opposite side. If that's your intent then an innertube may be sufficient. I'd still opt for the PVC, personally, but at that point I don't know that it would be necessary.)
The idea for boarding is to suspend one or two stirrups on a rope or strap from the outrigger arm right at the point where it meets the canoe. That way the diver can grip the gunwale and the outrigger, climb with their feet in the stirrups, and swing a leg over into the boat.
for the record my wood and fiberglass boat is far more durable than any plastic boat I've ever seen and, with the right skin, skin on frame boats will "drag" (though I'm not sure why you'd want to since they're so light) over pretty much any surface that isn't an oyster bed. Most will even drag over oyster beds if they aren't fully loaded. Either way both are far more easily repaired than a plastic boat other than the surface scratches you mentioned in your post.
A well made boat of cedar strips or fiberglass is a joy in and out of the water compared to rotomolded plastic. This is true of kayaks and canoes alike.
Comments comparing differing experiences aside, you're overlooking the fact that OP already has a boat. While it's nice to be able to spend "under $1000", it's not practical for everyone. Some people don't have space to store multiple boats. Some don't have the money to buy (or build) multiple boats. The list of reasons against buying a new/different solution are endless. By the way, you can get stitch and glue wood and fiberglass boat kits starting around $700 and that's 10x more than I paid for any one of my multiple skin on frame boats. Either option also can be designed and built as a SOT.
OP already has a boat, suitable for the other uses he has for it (not likely the case for a SOT kayak) that can be easily modified/added to for the times when he wants to dive from it. IS it the solution for every problem? No. It is a solution for his problem.
Thanks, fjpatrum, you speak to my situation on a number of points. Keep in mind that a 17' canoe carries two people plus gear, so the comparison is between what I have now and purchasing two kayaks, since as far as I know, kayaks that will comfortably carry two divers and gear are not available. Devoting the money and space to two additional boats is not a lifestyle choice I wish to make.
fjpatrum, I read what you say. I wished you guys success. It sounds like a PVC outrigger might be the easiest solution to providing some needed stability with the outrigger poles clamped to the thwarts. Still do not understand how he is planning to re-enter but perhaps the area will allow him to stand on the bottom and simply hop in. Some of those "rivers" in Florida are private property to the water edge so this limits one to entering and exiting for that matter from the water so as to avoid confrontations with often rather difficult property owners. But if he can beach it without any trouble like that then he has it all pretty easy to work with the canoe.
I'm using the boat in Minnesota (not Florida), and yes, many of the rivers here do have private ownership to the water's edge in many places and there do exist situations where a shallow entry is all that's necessary. As I outlined above, though, I'm envisioning my setup as being workable for deep water as well.
On the thwarts, maybe a piece of PVC and drill and attach to the top of the thwarts, from the ID. Then size the outrigger tubes (aluminum tubing) to slide into the PVC tubes attached atop the thwarts. Then install the parts in assembly and cross drill for a 1/4 inch push/hitch pin to lock them in place? On the outrigger side, something similar, that way it could be disassembled and stowed if not needed in passage. Just trying to think of a way to do it that does not involve a large contraption or much modification of a nice boat.
I think I can just lash it down to the yoke on both sides, next the gunwales, with the arms fixed in place laterally as well as fore to aft by the blocks in the photo upthread.
I notice I said my canoe was 14 feet, actually it is 16 feet and a bit. Just for accuracy. Had a lot of fun with it. Hope you both have fun and success with your plans.
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Thanks, mine is 17' as I noted upthread, good sized for two people.[/quote][/QUOTE]