03-26-2023, 10:40 AM | #21 | |
Join Date: Sep 2011
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Re: Gurps vehicles to design boats?
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In general it translates to the mechanics in the game. Of possible note is that Vehicles also has chapters providing additional rules sections on Advanced Vehicle Movement, Special Movement Rules (Ground, on or under Water, Flying), Sighting and Detection, and Combat. Vehicles Expansion 1 adds spherical pressure hull, advanced submarine lines and supercavitating hull to Hydrodynamics and hull design options. It subdivides the types of rigging given in Vehicles into sub-types with revised sail areas and, for the first time, a Maximum Upwind Angle in degrees, which is the minimum angle between the prow and the wind which will still allow the ship to sail, varying from 105° to 20°. It offers an expansion from the wind effects on sails (p. Ve30) covering Forces 8-12 on the Beaufort scale (and recapitulating Forces 0-7), an Expanded Movement Rates and Sailing Table which covers the five different points of sail (On the bow (tacking), On the bow, Abeam, On the quarter, Stern), and Submerged Performance Statistics (revised Crush and Test Depth, and Supercavitation). Vehicles Expansion 2 adds Pontoons and Rigid Sails (Flettner rotors, Wingsails and Turbosails), along with a table for rigid sails which covers four of the sailing points (no On the bow (tacking) entries). New Propulsion information for: Paddling and Poling options as alternatives to rowing (initially presented in Low Tech; Feathered Paddlewheels; and Aquatic Flexibodies. It also includes an option for Active Flotation, an aquatic lift system. I hope this will be useful in sorting out what fulfils your needs. Last edited by Curmudgeon; 03-26-2023 at 10:53 AM. |
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03-26-2023, 10:51 AM | #22 |
Join Date: Jan 2006
Location: Central Europe
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Re: Gurps vehicles to design boats?
The same would be true if you took a wooden boat with a low freeboard (eg. a Rhine River barge in 1940) and dumped extra load on board
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03-26-2023, 04:07 PM | #23 |
Join Date: Dec 2009
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Re: Gurps vehicles to design boats?
Thanks for the breakdown that really sounds great.
My world consists of lots of small islands. Where one town/village is on one island, so lots of fishing and ferrying pax and cargo/trade back and forth. Of course the aquatic monsters that run the underwaters between them… It might be fun to have occasional sail races as part of the local entertainment. So I do need to drill down into the details when I need to. This sounds like it would allow me to do so. |
03-26-2023, 04:43 PM | #24 |
Join Date: Jun 2005
Location: Lawrence, KS
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Re: Gurps vehicles to design boats?
All right, let's look at an example, and one I'm somewhat familiar with: an Athenian trireme. Length: 120 feet. Beam: 18 feet, but that includes superstructures that extend out to the sides to give the top rank of oarsmen seating. Loaded weight: 77.7 tons.
A trireme is designed for ramming, which requires high speed. So let's assume that its hull has a beam of 15 feet (with an extra 1.5 feet on each side for the superstructure), giving it a ratio of 8:1 for Fine lines. This will give it a flotation rating of 48 lbs. per cf. So to float 77.7 tons, it needs 3237.5 cf. The formula on p. 16 of Vehicles gives it a volume of 35 cf per displacement ton, or 2719.5 cf. Applying a multiplier of 1.3 for Fine lines gets us to 3535.35 cf. We'll use the larger figure. Draft is the cube root of loaded weight in pounds, divided by 15, times 1.3 for Fine lines. That comes out to 4'8". Multiplying draft by flotation, which is 169,696.8 lbs. or 84.85 tons, and dividing by 77.7 tons, gives height of 5'10". Since draft is 4'8", freeboard is 1'2". Looking at photos of the Olympias, a modern reconstructed trireme, I certainly get the impression that its deck is a lot more than 1'2" above the waterline! So I don't think this can be right. I'm left to suppose that the flotation rating is a significant multiple of the loaded weight. Indeed, I expect that many ships have substantially higher flotation ratings, and have a significant part of the hull riding above the waterline. But how do I estimate that? Vehicles doesn't seem to give any help.
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03-26-2023, 06:12 PM | #25 | |
Join Date: Aug 2004
Location: Wellington, NZ
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Re: Gurps vehicles to design boats?
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03-26-2023, 06:45 PM | #26 | |
Join Date: Jun 2005
Location: Lawrence, KS
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Re: Gurps vehicles to design boats?
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Bill Stoddard I don't think we're in Oz any more. |
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03-27-2023, 05:32 AM | #27 |
Join Date: Jul 2006
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Re: Gurps vehicles to design boats?
As I understand it, ship design is extraordinarily complex - besides the issues of freeboard and, like, not sinking, there's also those of leeway (mainly for sailing ships) and metacentric height and stability.
And all the weird stuff - for example, most of the pre-Dreadnaught designs weren't short of centreline turrets because their designers were idiots, but because vertical expansion steam engines took up too much vertical space in the hull, forcing the armament into sponsions and casements around the outside. For lower tech stuff - I recall the mutual hinderance problem with rowed vessels was such that, once the trireme hadn't be used for a while, no-one could figure out how to work three banks of oars together again until long after it stopped being useful to do so. |
03-27-2023, 06:15 AM | #28 | |
Join Date: Jun 2005
Location: Lawrence, KS
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Re: Gurps vehicles to design boats?
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Bill Stoddard I don't think we're in Oz any more. |
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03-27-2023, 06:47 AM | #29 | |
Join Date: Jul 2006
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Re: Gurps vehicles to design boats?
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Plus, IIRC, you needed skilled oarsmen, and it was simpler to put more men of fewer oars. |
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03-27-2023, 07:44 AM | #30 | |
Join Date: Aug 2004
Location: Wellington, NZ
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Re: Gurps vehicles to design boats?
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Another factor was that the nature of naval warfare changed, and ramming became less important, and with that the need for extremely agile and fast warships. The ability to carry troops and artillery (and be a decent artillery platform) became more important.
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