How long is a piece of string?

In naval architecture there are three key length measurements.   Stating the length of a ship without giving the qualifying unit is, like you said asking the length of a piece of  string.

Waterline Length (WL)  - like it says this is the length of the ship at the design waterline,

Length Between Perpendiculars (LPP) - this is the length from  the forward perpendicular which is something like the first vertical strake at the stem -- to the stern, ususally the rudder post.   The forward perpendicular may be forward of the bow at the waterline. 

Length Overall (LOA) - this is the overall length of the ship, including projections fore and aft.

Model manufacturers are not generally cognizent of these distinctions.  They just want to let you know that a model will fit onto a shelf.   And the guy who wanted to RC a HMS Victory should have been wise enough to ask how far the bowsprit projected.

I can't fault either.

Plastic kit manufacturers - and, come to think of it, wood kit manufacturers too - are utterly notorious for their casual approach to scales and dimensions.  In a recent discussion of the various H.M.S. Victory kits on the market, we established that the scales stated on the boxes of most of those kits bear little if any relation to reality.  For example, Airfix says its Victory is on 1/ 180  scale, and Revell says its is on 1/146 - but the Airfix kit is bigger.  (The actual scales work out to about 1/171 for Airfix and 1/220 for Revell.) 

It's hard to tell how much of this practice is deliberate deception and how much stems from genuine ineptitude.  The sad truth is that the people writing the advertising copy for these kits frequently know next to nothing about the subject.  In any case, let the buyer beware.  I've reached the point where I don't pay much attention to the stated dimensions and scales on kit boxes any more.