Forgive me, but I do not have the ISAF book here at work so I can’t quote, but I think the intent is to measure the total volume of water in the cockpit before draining. So it should be the lowest coaming except for the bridge deck before the companionway. What boat do you have? My Catalina passed ISAF Ocean 2, but I have a sugar scoop stern. My bridge deck/companionway threshold had to be at least as high as my cockpit
seats which I achieved by fixed mounting my lower
hatch board in place. In the for what it’s worth department, I’ve been pooped twice (once severely) and in retrospect, it wasn’t so bad as none of us got flushed out. I was surprised how quickly we drained once the stern got out of the wave. We did have the
hatch boards in place and the slider closed so we had the minimal amount of downflooding.