: When sizing a spray skirt do you measure from the outside of the lip?

I guess its too late for you to follow my example - I looked at stock
sizes of spraydecks made by Knoydart kayaking systems, and read off the
range of sizes fitted by their smallest, the Ocean 1. Then I had a quick
check of some boats these were meant to fit (like the Valley Anas Acuta)
and built my cockpit to those dimensions, working back from the outside
lip size to derive the line to cut out on the deck. My coaming lip is not
huge, but the spraydeck is a perfect fit and doesn't leak, with an inside
dimension of about 23x17 inches.

: My
: cockpit is very large. I want to make sure I get the right size. May even
: have to have it built.

With a very large cockpit, you will be leaning forward a lot more to get the
spraydeck on, which most people find harder - you may not want your deck to
be a really tight fit for this reason, though for every other reason, it is
better to have a very tight fit - less likely to implode in a breaking wave,
less likely to leak along the long straightish sides in a big beam sea - and
if your knees can press on the spraydeck, it doesn't need to be as easy to
get off by pulling the tab.

Andy