Age of Sail & GURPS VEHICLES 2nd edition

[hal]

Hello Folks,
For the longest time, I had worked on trying to stat out Age of Sail ships using GURPS VEHICLES 2nd edition, and having a problem with using the recommended ton displacement = 35 cubic feet rule.

As luck would have it, while trying to determine how the Spanish would determine Tuns Burthen versus how the French determined tons burthern as contrasted versus how the English determined Tons burthen are a wee bit differnt. In general, the French values for Tonnage of a ship worked out to be roughly 40 to 50% larger than the British values.

While looking up the Wikipedia entry on Tuns Burthen, I stumbled across this nugget:

Tons Deadweight = 3/5ths of its displacement.

As luck would have it, the formula for Tons Deadweight, matches exactly the tons Burthern Old Measure given in a few of my books.

So, with that discovery, 3/5ths of the displacement of the vessel would be such that some 40% would be above the waterline, while some 60% would lie under the waterline. As a consequence of this, suggested volume for a ship's hull where you know its tonnage burthen (the British tonnage values for a good deal of warships for example) would be equal to 5/3 x Tons Burthen x 35 cubic feet.

Refined: 1.67 x Tonnage x 35 cubic feet

or

58.33 cubic feet per tons burthen

For what it is worth, all of the time I had been experimenting with trying to get the hull statistics right along with mast length statistics, left me throwing up my hands in disgust and giving up. For a time there, I had been using 70 cubic feet per displacement ton on the theory that half of the hull was below the waterline and the other half was above the waterline. That didn't seem to work too well.

Mast height of the tallest Mast:

(Length of ship x Beam)/2 where Beam is the width at its widest point.I'd have to look up what the ratios were of the Foremast and the Mizzen mast as compared against the Mainmast, and when I find it again, I'll post it here.

Thought I'd share this snippet of information. :)

Added information:
Main mast: (Length+Beam)/2
Fore mast: 8/9ths Main mast
Mizzen mast: 6/7 Main mast
Main Topmast: 3/5 length of Main mast
Fore Topmast: 8/9 Main Topmast
Mizzen Topmast: 3/4 main Topmast
Main Topgallent mast: 1/2 Main Topmast
Fore Topgallent mast: 1/2 Fore Topmast
Mizzen Topgallent Mast: 1/2 Mizzen Topgallent mast
Bowspirit: 7/11 the length of the Main mast


So, for example: A ship with a length of 170 feet, a beam of 47.5 feet, would have had: a main mast of 108.75 feet.
Main mast: 108.75 feet.
Fore mast: 8/9ths Main mast or 96.67 feet
Mizzen mast: 6/7 Main mast or 93.21 feet
Main Topmast: 3/5 length of Main mast or 65.25 feet
Fore Topmast: 8/9 Main Topmast or 58 feet
Mizzen Topmast: 3/4 main Topmast or 48.93 feet
Main Topgallent mast: 1/2 Main Topmast or 32.63 feet
Fore Topgallent mast: 1/2 Fore Topmast or 29 feet
Mizzen Topgallent Mast: 1/2 Mizzen Topgallent mast or 24.46 feet
Bowspirit: 7/11 the length of the Main mast or 69 feet.

As best as I can figure then, the average height for this ship (a 74 gun ship by the way) would be in the vicinity of:

Main Mast: 108 + 62 + 32 or roughly 202 feet total. I don't know how much the masts overlap each other, but the mainmast length includes that portion beneath the hull itself butted against the keelson. So subtract the depth in hold from the masts themselves and that would be (presumably) the length of mast above the decks. How that relates to the GURPS VEHICLE DESIGNER or GURPS VEHICLES rules - I can't say.

[hal]

Silly me - almost forgot to add the formula for Old Builder's Measure for Ship's tonnage:

(Length of Ship x Beam (width) x Beam/2) / 94

Note that his formula is for English ships, not French. French ships were in theory, some 50% larger in that While the British would have specified the ship's tonnage as 600, the French might have listed it as 840 to 900 ton.

[whswhs]

Yes, I ran into those problems in doing ship design. As you say, the 35 cf formula only works for the part of the ship that's below the waterline, and unless it's a submarine, that's not the entire ship! There's actually a lot of variation; for example, I believe the original Monitor was something close to 90% below the waterline. I ended up using various bugger factors to give the ship more volume than its loaded weight implied by that rule; I hadn't seen the rule of thumb you cite.

Bill Stoddard

[hal]

Originally Posted by whswhs

Yes, I ran into those problems in doing ship design. As you say, the 35 cf formula only works for the part of the ship that's below the waterline, and unless it's a submarine, that's not the entire ship! There's actually a lot of variation; for example, I believe the original Monitor was something close to 90% below the waterline. I ended up using various bugger factors to give the ship more volume than its loaded weight implied by that rule; I hadn't seen the rule of thumb you cite.

Bill Stoddard

The 3/5ths rule that I cited was quoted in this Wikipedia article. I have since discovered that if you try to print that article out using the Print command under "File" for the web browser, it truncates the printed material. However, if you look on the web page itself, there is a print function that prints it as a PDF that you can download to your computer.

As I said, I had been using as a fudge factor of my own, the rule of each tons Burthern was about 70 cubic feet (ie double the 35 listed in GURPS), but I was getting odd values when I finished the attempted design. Now I'm going to have to relearn how to use GURPS VEHICLE BUILDER and see if this doesn't help a little bit.

ADDED THOUGHT: While I'm thinking about it, the Block Co-efficient of .62 could probably be tweaked for those craft that are more or less sleek than average. I recall reading that the Builder's Old Measure didn't really fit all hull types, and that it was off for the sleeker hulls. If you would like, I can either email you the bibliography of the books I'm using, and the one that specifically had the Builder's Old Measure that I had been using before I recognized it as the Deadweight measure in the Wikipedia article :)

[nik1979]

will you be making a modular system? Is there a Age of Sail GURPS ship combat system?

[copeab]

Originally Posted by nik1979

Is there a Age of Sail GURPS ship combat system?

For 3e, yes. It first appeared in Swashbucklers and later Compendium II.

[hal]

Originally Posted by nik1979

will you be making a modular system? Is there a Age of Sail GURPS ship combat system?

I've not the smarts for creating a modular system alas. As Brandon notes, there are rules for ship to ship combats in swashbuckler, but I never really did like it's level of abstraction. Also, it tends to skew the combat results when you have a ship that has even a single 3 lbr cannon going up against an unarmed ship - this despite the fact that the ship with the 3 lbr might be going up against an East India ship or a Spanish Treasure Galleon - where those 3 lbr cannon balls aren't really going to have all that much of an impact.

As has been mentioned elsewhere, you may want to get your hands on a copy of RUN OUT THE GUNS by IRON CROWN ENTERPRISES from Ebay. Unfortunately, it is out of print and is relatively hard to find. If you can get your hands on a copy, it comes with a very colorful map of the Caribbean, along with the rules for what amounts to ROLEMASTER's game system just for the age of piracy time period. It has a fair amount of information in it, although the one problem I found with it is that just about all the ships have the same hit points and sail hit point levels along with similar floation hit values. But - despite the minor warts, it is well worth getting your hands on. If you love the era, don't let the opportunity slip by if you ever get a chance to buy a copy. You won't regret it.

[Phaelen Bleux]

I have been using the Builder's Old Measure as well, but the formula I found was:

[(Length - (0.6 x Beam)) x Beam x Beam]/188 = tons displacement

Then I have been multiplying by 100 for cf.

I like the formula for tallest mast though. . .the formula in Vehicles always gives masts that are ridiculously tall.