I have a recollection that the height of the Wormwood's masts are stated in the Wormwood Mutiny when the PCs are told to race to the top of the mast. I can't remember it right now but have always used that number when it's come up. I know for sure that in Tempest Rising mast heights are mentioned during the test to become a Free Captain.
As far as water line to deck, I have always said it was 15 feet for most sailing ships. Although I think I just made that up, it might be stated during the boarding training event in the Wormwood Mutiny. For larger battleships, there is a diagram of the Dominator in Raiders of the Fever Sea you could use that displays this. I wouldn't use this number for most ships though as the Dominator is stated to be an unusually big boat
The only ship I remember seeing such info for is the Wormwood in the first book. And I think the distance from the deck hatch & middle hold were listed at 15' for the Man's Promise.
the 15 to the water seems right, ill have to wait till I can check the book for the mast height, I forgot about the climb at the beginning.
Ok, pulling WWM off the shelf....
For the Wormwood (the ship my pc's are using):A1) Foredeck - 10' above main deck
the foremast rises 30' above this.
A2) Poop deck - 15' above main deck
The mizzenmast rises 30' above this.
A3) the main deck
The mainmast rises 60' above this & is topped by the crows nest (plugs test tells us the crows nest IS at the 60' mark)
A6) Middle deck - 15' below the main deck.
A10) Lower deck - 10' below the middle? Not specified, but the map only shows 10' of stairs...
A11) Bilge - depth not specified at all. We just assumed "room for a normal human to stand".
The Man's Promise:
B2) Foredeck - rises 10' above the main deck
B3) Aft deck - rises 10' above the main deck
B4) Sterncastle- rises 20' above the main deck
B8) Middle deck - 15' below the main deck.
B12) Main hold - not specified how far below the middle deck. But only 10' of stairs are shown.
Bilge - mentioned as being fore, aft, & contains more spiders than the Wormwood.
Masts: not detailed at all.
And the masts used in Tsardoks test? 60' tall with arms at least 60' wide on an entirely different ship (the Stingray)
Very roughly speaking, the top of the tallest mast should be about as tall as the ship is long. If it's much longer, the leverage of the wind will probably capsize the ship; if it's much shorter then there won't be enough sails to provide good thrust.
The mathematical backing of these assertions is left as a trivially obvious exercise that is part of your graduation from the Portsmouth School of Naval Architecture, Professor Bernoulli, Principal.