John

One idea that I had when wanting to get offsets from an existing kayak
(to study it, rather than to copy it, as it happens) was to make a narrow
slit in a piece of cardboard or ply wood, through which to fire a flash gun.
You would put the camera on a tripod somewhere level with the kayak waterline,
and some way in front of the bows, then move the slitted card a foot at a time
along the length of the boat up to the biggest section, firing the flash at each point. Then repeat for the stren, viewing from behind. You'd need to
image a metre rule or something similar at each end of the boat to allow for
perspective. The idea would not work well on a dark-coloured boat such as
a carbon one. You'd also need to be good at working in the dark if you were to take all the sections on a single exposure, although you could put the lens cap on between flashes whilst you moved the slit.

I never got round to trying this idea, as I found enough documented boats to
study without needing to do this ...

Andy