: Oh, and you may find your kayak feels less stable in salt water.
: It's not
: an illusion. Salt water is denser than fresh water, so your kayak
: will float higher.

: So much for displacement numbers!

It does makes a difference, just not a HUGE one. See below.

Per high school science class, taken at sea level and 77F, the specific gravity of pure water is 1.000. Fresh water is close enough to pure so we'll keep that 1.0. For salt water it's around 1.025 (depending on where you're paddling and the current temperature. The North Atlantic is higher than the South Atlantic and much of the Pacific. Anyway...). That change will throw off a 250# displacement by a massive 6.25 pounds (ish). Now let's take Nick's "Night Heron" as an example. He graciously lists the sinkage as 84 lb/in. So that big 6.25 pound change amounts to a grand total of a 1/16"! Not sure how many paddlers could tell the difference...

I know of very few kayak designers that will tell you if the design displacement is for fresh or salt water. I would assume fresh and back-calculate if it's a life or death concern.

It probably doesn't really matter but when I'm designing a kayak I look where it's going to be paddled. For an 18' sea kayak: I use SG for salt water. A 13' solo canoe: fresh. It's a simple project option on the design software I use. If in doubt just ask.