: A true max displacement would be the total volume of the kayak
: submerged, but that's usually not a practical way to paddle. :)

Yep, MAX displacement is when the canoe body is immersed to the point where openings, such as cockpits, unsealed hatches, cabin companionways, etc. begin to take water in an upright condition. If all the hatches and the cockpit are sealed, such as you might find on a sea kayak, for instance, then the MAX displacement is the total immersed form. If it's a sealed form, such as an ama on a multihull, it is also the full immersion figure.

With the exception of amas, which seldom have total displacement figures given as a function of weight supportable, the reference of Displacement virtually always refers to the DESIGN DISPLACEMENT by the designer, as it is intended to be used. For my design work, I list a design displacement figure that is my estimation of the load carrying ability of the hull when it is very near to its best all-around performance. It is intentionally a bit lower than what the boat can carry at full design load. A Fudge Factor, if you will. I put this in place, because owners will invariably look upon the displacement figure as their green light to stash more gear than they really need. As often as not, they exceed the stated figure because they really do not know the weights for all the stuff they will cram aboard. The result… they have a boat that is excessively draggy and sluggish to turning input.

When you come right down to it, and this is especially true for a surprising number of production boats, all of these stated specification figures can be regarded as Marketing Light estimations. Lots and lots of boats do not measure to their listed specs. Even though the exacting guy who did the design arrived at a very specific set of numbers, the folks in the marketing department have been known to let the numbers drift a bit because they look better on paper when compared to the competition.

Want to know the real deal on your boat... get out the tape measure and calculator and do your own set of figures.