The problem with ship construction rules that encompass both a longship and a galleon are that technology changed so much from 800 AD to 1700 AD that the whole process was literally 100% different.
This was the problem we encountered when trying to design a codified set of rules for Broadsides!. The ships we list are historically accurate to what they could actually accomplish, and because we cover over 900 years of naval advancement, it's impossible to set a system up. Longships were the pinnacle of advancement in 800 AD. Using 800 techonolgy, it's impossible to make a 2 or 3 masted ship. On the other hand, when you're in the Carrack or Galleon era, oars were phased out for the most part. Putting a bunch of oars on a ship like that was not only pointless, but would reduce the overall effectiveness of the design.
We actually explained that in our brief section on Ship Construction. To do it right we would have to have a different set of rules based on each era of naval techonolgy. Since that was impractical (and would have taken up dozens of pages), we decided instead to lay down some helpful guidelines, and left the rest to the DM.
Also to address a point that Psion brought up in the review - the lack of deck plans was not an oversight. Deck plans are huge and complicated, and dont' translate well into the D&D 5' scale standard. Since most of our ships are historically based (unlike SH and SoB, which use mostly fantastic ships), we didn't want to crowd the book with innaccurate or unusable deck plans. We wanted to stay as historically accurate as possible - we did so for the stats, why would we forsake that for some maps?
We are currently looking in to providing deck plans for all of our ships on our webpage, but I cannot say for sure if that will come to fruition.
Regardless - Psion - I thank you for your review, and I'm glad you think that we can successfully go toe to toe with the "Big Boys". We are proud of our system.