Kayak Sizes question?

Can anyone explain if the difference in k1 sizes. Is it just the size of the deck (volume), cockpit size, or hull (volume) or a combination of all 3?

Nelo, Vajda etc advertise their k1's in sizes for different weight paddlers. The only difference I can see is in the cockpit size?

I guess what I'm asking is the XXL the same size and shape hull as say a medium?

Cheers.

Good question. I've assumed the same thing, that the hull profile/shape is merely extended above the waterline to give more width and volume.

The hulls can be very different between the sizes.
Because you cannot extend the hull length the hull shape has to accommodate the extra weight. Look at the stern of some of them you will see how different they are.