NavList:

Ever hear of a cruise line or any ship owner or captain who couldn't answer that question?  My parents took a cruise in the 1970's and the little ships information booklet loved to list all the statistics from length of deck to height from waterline or plimsoll line really. Density of water changes and loaded and empty ships have different dispersement ratios.

I am sure every steward knows where to find the answer.

Algebra and geometry can find the height of buildings with formulae, therefore finding the answer can be had of your dip on the boat deck, one might think.

Paul Hirose, you asked:
"How do you determine height of eye on one of these vessels?"

The easiest way is from a photo of the vessel. Yesterday in the FB celestial navigation group, someone posted some Sun observations with no indication on height of eye. He did post his coordinates which were on the east side of the Kattegat (between Sweden and Denmark), mentioned that they were at anchor there again, and said that he was taking sights from a bridge wing. So we pop onto the marinetraffic website, discover there's only one ship that fits the bill, and look up photos of it online. When you find a photo that is more-or-less beam on (a side view) and if you know the length overall of the vessel, you can easily determine the height of any point above the waterline. There's some ambiguity depending on loading of the vessel, but this gets you very close.

Frank Reed