Hi.
I usually try to find pictures taken straight from beside, front, back or from the top. Then I start mark / pick the mesurments that are known. Usually you know the owerall lengt anb breath of the ship. And often it is standard type of doors, and other visible equipment on deck that you can use to find "secure" mesurments. And in about 90% of modern (since the 1980) naval & sivilian ships, the deck spasing betwen deck plates (Examble: distance between A and B deck) is 270cm / about 107 inches.
Then when you have found all known mesurments, its just an advanced game of find the X, use a calculator and a scale converter app. And just start.
Would recomend to keep all numbers in one format at first, then convert them to the scale you need
Good luck on your task.
My i ask wich ship you are gona work on ??
Ps: Sorry for my bad English.