Gurps vehicles to design boats?

[Rupert]

Originally Posted by whswhs

So does this mean that three-banked oars were a unique product of Athenian genius?

Nobody is quite sure whether they're a Greek or a Phonetician development of the bireme, but they don't seem to have come from Athens. They just made very effective use of them.

[Fred Brackin]

Originally Posted by whswhs

So does this mean that three-banked oars were a unique product of Athenian genius?

Probably just that using them was a lost Skill (that may not have had a usable default).

The situation with pikes might be similar. Actually using massed ranks of pikes without getting them fouled with each other is a definite skill that was probably lost 2 generations after armies stopped using pikes. Nothing that re-enactors couldn't teach themselves but requiring more effort and particularly longer training than anyone had time to invest in it.

[David L Pulver]

Originally Posted by whswhs

The thing that has long perplexed me in GURPS Vehicles is figuring the volume of boats and ships. GURPS Vehicles envisions a ship as a rectangular prism, which has length, width (beam), and height (draft). Total volume is the product of these three, and a ship's ability to float is based on its volume. I find all this so perplexing that I can't really feel at ease with ship design in GURPS Vehicles.

In GURPS Vehicles, length, width, and height are not significant elements of the design system. They are color details.

The system - as the design system indicates - is designed around selecting the contents of the vehicle e.g., a ship might hold 100,000 cubic feet of cargo, 20 cabins, an engine, fuel, etc. - and then, after you have determined this, wrapping a hull of a given volume around it. (You might also designate some of these components are in a superstructure, or turrets, etc.)


The reason for this is that while ships are somewhat nice geometric shapes, sort of, many other vehicles - especially aircraft - are not. Trying to model the individual geometries of these things - or even a ship with multiple superstructures - in terms of length, width, etc. - is just a freaking nightmare without complex computer programs. It might work for a galley, but the system is supposed to be universal.

So, if you attempt to use Vehicles in a way that it is not designed - for example, by specifying lengths, widths, and so on and then going from there - you'll tie yourself up in knots and have problems. It would be like designing a GURPS character's strength and hp by careful calculations of their bicep sizes, fat ratios, and BMIs and then complaining the system won't do what you want.

[David L Pulver]

Originally Posted by briansommers

I’m using 4e but I’m so tempted to get 3e vehicles because I really want to design TL3 boats.

How detailed does this get?
I want to choose shape of sail, size of sail, length & width of boat, different levels, number of sails, where I place them, etc. can I do all of this with vehicles?

If you have the Vehicles core book you can chose the size of the sail, number of masts and you can specify the volume of the vehicle and its hydrodynamic shape which determines its general dimensions. If you have the correct vehicles expansion supplement you can choose more detailed sail types.


However, Vehicles fundamentally is designed to build things of any size and shape from rowboats to helicopters to powered armor to ornithopters. As a result, the system is very "ground up". Fundamentally it's about assigning components with defined or user-designed volumes and weights to specific locations (the main body, the superstructure, etc.) and then after that you know the general volume of each part of the vehicle. Then some calculations for things like (in the case of boats) area of sail compared to the vehicle's size and weight determine how fast it goes, the weight of the vehicle compared to the volume of the body determines whether it floats, and so on.

This is all at a very high level so that the system can do everything with a single system. You won't find serious discussions of freeboard, metacentric heights, and so on; even specific lengths and widths are somewhat abstracted, as the system is focused on volume, surface area, and weight in order to handle a huge possible variety of shapes.

I've long played with variations that would let you start with dimensions and then derive values, but by and large they don't work because vehicles aren't boxes or spheres, and that leads to a huge level of complexity once you start going beyond very simple hull forms. If you want that, I recommend playing with some of the computer design systems that have sprung up instead.

[whswhs]

Originally Posted by David L Pulver

In GURPS Vehicles, length, width, and height are not significant elements of the design system. They are color details.

The system - as the design system indicates - is designed around selecting the contents of the vehicle e.g., a ship might hold 100,000 cubic feet of cargo, 20 cabins, an engine, fuel, etc. - and then, after you have determined this, wrapping a hull of a given volume around it. (You might also designate some of these components are in a superstructure, or turrets, etc.)


The reason for this is that while ships are somewhat nice geometric shapes, sort of, many other vehicles - especially aircraft - are not. Trying to model the individual geometries of these things - or even a ship with multiple superstructures - in terms of length, width, etc. - is just a freaking nightmare without complex computer programs. It might work for a galley, but the system is supposed to be universal.

So, if you attempt to use Vehicles in a way that it is not designed - for example, by specifying lengths, widths, and so on and then going from there - you'll tie yourself up in knots and have problems. It would be like designing a GURPS character's strength and hp by careful calculations of their bicep sizes, fat ratios, and BMIs and then complaining the system won't do what you want.

That's all very well, but in the first place, I'm talking simply about the hull of a ship, or in other words its main body, which avoids all those problems about superstructures and the like. In the second place, Vehicles DOES give a formula for draft, based on weight and hull configuration. And in the third place, hull configuration is based primarily on length:beam ratio. So telling me just to ignore a ship's length, beam, and draft contradicts the rules as written.

What I'm trying to get is an idea of how deeply a ship rides in the water. With a normal load, is it skimming along on its lowest few inches, or submerged about halfway up the hull, or almost up to the gunwales, or something in between? I find it plausible to have that depend on the ratio of loaded weight to flotation (at least to a first approximation; it's only exact for a ship that's a rectangular prism, like a barge). But I don't have any guidelines for how much flotation ships of different types should have, or for how many pounds of loaded weight per cubic foot are typical for different types of ships. Obviously a merchant cog laden with cargo is going to be a different case than a trireme ready to ram the enemy, and both are different cases than the original Monitor. And it would be a big help to have suggestions.

[Polydamas]

Originally Posted by Rupert

Nobody is quite sure whether they're a Greek or a Phonetician development of the bireme, but they don't seem to have come from Athens. They just made very effective use of them.

Thucydides says that triremes were first built in Greece at Corinth. What "in Greece" modifies has been debated since the Assyrian reliefs were discovered in the 19th century.

[Rupert]

Originally Posted by Polydamas

Thucydides says that triremes were first built in Greece at Corinth. What "in Greece" modifies has been debated since the Assyrian reliefs were discovered in the 19th century.

And others suggest Sidonia, and did Thucydides mean "introduced into Greece at Corinth" or "invented by Corinth", so it goes. Certainly the Athenians were not the first to have a large fleet of them.

[Rupert]

Originally Posted by whswhs

And it would be a big help to have suggestions.

Some (very) rough estimates, based on reading and observation, but not many firm numbers (because finding sources that give both freeboard and draught and load state all at once is surprisingly difficult for the lay reader).

20th century battleships and pre-dreadnoughts: freeboard about equals draught at light or normal load and they get deeper from there. Variance is towards less freeboard.

Other 20th century and very late 10th century warships: 1/2 to 1/3 submerged, depending on armour.

20th century merchants: Start with very little draught, but at full loads 1/3rd or less of their height as freeboard is common. Container ships tend not to lose as much freeboard, despite having containers on deck stacked half a dozen high, because containerisation might make moving freight fast and efficient, but individual containers tend to be quite lightly loaded (and even at maximum gross weight a 20' container is less dense than water, and a 40' or high-cube one rather less than that).

Age of sail ships start at about 1/3rd submerged, going down to 1/2 or even 2/3rds submerged when heavily laden. Warships were limited by the freeboard to their lower gun decks.

I have real idea when it comes to older ships like triremes and longships.

[David L Pulver]

Originally Posted by whswhs

What I'm trying to get is an idea of how deeply a ship rides in the water. With a normal load, is it skimming along on its lowest few inches, or submerged about halfway up the hull, or almost up to the gunwales, or something in between? I find it plausible to have that depend on the ratio of loaded weight to flotation

Sure, isn't that the simplest solution?

Loaded weight in lbs./buoyancy (i.e., 62.5 or 64 x body volume) = the amount of the hull submerged. E.g., 2000 lb. weight and 4000 lb. buoyancy = 0.5, so 50% submerged. If 1.0 or more, 100% submerged, it sinks.

Flotation factor (e.g., 0.5) x height = draft, yes? Freeboard = height - draft.

(In V design I derived height as length x lines: 1 for poor, 0.5 for fair, 0.3 for average, 0.25 for good, 0.16 for very good, 0.14 for superior, 0.125 for excellent, and 0.12 for radical.)

[David L Pulver]

Originally Posted by Rupert

Age of sail ships start at about 1/3rd submerged, going down to 1/2 or even 2/3rds submerged when heavily laden. Warships were limited by the freeboard to their lower gun decks.

I have real idea when it comes to older ships like triremes and longships.

It's one of those things that are nice to know, but which rapidly fill up the book, like listing wing areas or whatever. The problem is, how do you succinctly specify and explain this when boat and ship names vary dramatically from TL to TL? "Trireme" or "age of sail ship" - okay, but what about medieval cogs or ocean liners or gunboats or dreadnoughts or barges or rowboats or power boats or aircraft carriers or passenger ships or freighters or rafts, all of which have very different examples?

This was something I struggled with a lot in VEHICLES - how to give meaningful examples when terminology changes. Especially when just saying something often means nothing unless the class of vessel is further defined.

Mind you, I agree it's a useful distinction. In this case, I think a better approach would be to distinguish between coastal or riverine craft (triremes, boats, etc.) and ocean-going vessels and specify a wide range for both...


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