yani

Here's one way of possibly saving a kayak
that is going down, filled with water.

Under the water, upright the kayak to full vertical,
nose first. Open its first hatch, closest to the
nose. Push the kayak upward, draining the kayak
as you push it up. Open the next hatch, if possible
to continue draining. Ect...

This will partially drain and allow it to float so you can deal
with it. Whether you keep it upside down or rightside up.

Maybe this will not work everytime, because you have alot
of wt inside, or the water is too choppy. But keep this option
in the back of your mind...