I really like the idea of a day hatch and the safety and structural advantages it bestows.

But what about using it horizontally too? Say the 2 bulkheads were at least the width of the widest paddle you can find apart. Say as low down on the shear as possible (say the neutral axis near the c/l as viewed sideways) you cut a slot on each side as wide and thick as this widest paddle blade. On both sides, inline with each other. Lets say 1in x 9in slot. one on each side

On the inside of this day hatch attach like an internal coaming lip all around each slot. Like one vertical strip and one horizontal (an L) for example and glass the *** outa it. And still on the inside, around each slot coaming lip affix a dry bag mouth. Say the dry bag is 12 wide by 24 in long(the approx slot and yak width) On inside bottom of the bag, sew/glue 30in of webbing and pull out the slot so 4 of 5 in hanging out.

Same thing on the opposite side, and link each coaming from one side to the other with a tube of netting to sorta keep each bag aligned. One will be on top of the other. Each side of the yak has 3 in thick or so of vertical ethafoam along the side, cut real wide for the slots to accept the opposite paddle ends.

To the day hatch screw cover(or real tight latch like airtight) drill in a flanged tube and attach a blow tube.

To use, push paddle in slot and blow on the blowtube to lock in place. The onside bag compresses around the paddle, while the offside bag tries to close off the offside slot trapping the paddle end in the foam.

But but but if no paddle or just resting or want relief or want more safety or want to support sick person:

pull on ea webbing tab while blowing, the dry bags evert, and you get Side Floats rigidly attached to the yak. TO get going again releas air, pull bags across ea other over the rear deck, Maybe a little velcro tab on each.

-mick

ps the issues would be to make the slots as low as possible, some experimentation w/ the internal foam to make paddle placement more smooth, the hatch cover must be gasketed and most likely small(say 6in diam or less) to be airtight, foam bulkheads too weak(say flex mounted hard ply or laid glass), but all probably possible