The purpose of the motor is to get me upstream so I can drift back to the car.
I'm not following mounting a motor "through a leg." I don't see a through hole in the photos.
I'm not seeing how to mount the tripod (or stabilizer boom) without piercing the bladder.
Thanks for the info re the center of rotation being at the center of buoyancy. I did not know that, and likely would never have thought of it.
I will be using a camera and lens combo that weighs 7 lbs. It's hard to imagine a boom that will be stiff enough without weighing a ton (hyperbolically speaking). I was planning to use a ground tripod to minimize the rotational moment of inertia.
Cedar waxwings are the epitome of elegance.
By "on a leg" think trolling motor or outboard. To mount all this stuff I am thinking of a box or platform that straps to the top of the board with extensions off the side or ends to mount things off of. If you don't have a box, everything you drop will bounce off the board and into the water. I suspected your camera might be large, heavy, and (I presume) expensive so there should be a fair budget dedicated to getting that camera home safe. Maybe the box could be a sort of wheelbarrow that you use to move the stuff to the waters edge. One of the best attributes of PVC is it's acceptance of glue.
That 7lb camera, does it take both hands to operate? If so, that is the next big challenge. FWIW I was thinking rasberry pi, my old iPhone 6+, or my action cams adapted to my film camera lenses or even my reflector telescope.
You need to give up thinking about stiffness and completely focus on stability and control. For example, I suggest you stage the SUV and float down to it while you shoot -at least for this season. If you were laying down on the board you could operate a pole anchor with you feet and even use a fin at the bow to point the board in the current (or the reverse face up). You could do the same thing along a lakeshore going downwind.
I have admired Waxwings from afar (in my kayak) but last night I got up close to see the exquisite detail. Viewsonic used a bird for their logo demonstrating high fidelity. Waxwings are my nominee -the subtle gradients and sharp edged colors will be a challenge.