[Spaceships] Nautical Lines and other underwater considerations

[vicky_molokh]

Greetings, all!

Spaceships 7 page 21-25 mentions Nautical Lines, and how they affect air speed. However, how do they (or lack of them) affect while swimming through a liquid (primarily water)?

Also, I'm curious if anyone knows if SS7 can be used for Vernian or other 'optimistic' underwater craft construction (in short, using Spaceships-based submarines with some rule additions for totally underwater campaigns).

Thanks in advance!

[munin]

Unhelpfully, I'll add to the questions. Do Spaceships spacecraft have any amount of Pressure Support? How deep into liquid or a gas giant can they dive? Is their ability to withstand pressure dependent only on HT, HP, and SM (as per p. B435), or does hull strength (dDR) get in there somewhere?

EDIT: The Tempest-Class Gas-Mining Cruiser (p. SS6:21) mines at 10 atmospheres, which implies at least Pressure Support 1.

[vicky_molokh]

More questions: which of the drives are best suited to represent water propulsion - Ether Screws, Rotary Reactionless, Helicopter Rotor, some sort of 'fuelless' Jet?

[vierasmarius]

Originally Posted by vicky_molokh

More questions: which of the drives are best suited to represent water propulsion - Ether Screws, Rotary Reactionless, Helicopter Rotor, some sort of 'fuelless' Jet?

A "fuelless" jet would work. I just compared the thrust-to-weight ratio of jets versus aquatic propulsion in VE2, and they're actually comparable (TL8 Hydrojet gives 20lb thrust per lb wt, TL8 8 Turbofan is 10lb thrust per lb wt). So we just need an appropriate equation to derive aquatic movement speed.

EDT: I just ran some numbers through the VE2 performance formulas. An SM+6 craft with 1 "Hydrojet" module (1G propulsion) and Very Fine Hydrodynamic Line has a top speed of 115mph surface, 42mph underwater. Switching to Submarine lines gives 80mph surface, 50mph underwater. Without Hydro lines it is 47mph surface, 23mph underwater. These seem workable, but I'd like to come up with a simplified formula suitable for the lower resolution of Spaceships.

[Purple Haze]

Real submarines are faster underwater than on the surface.

[vierasmarius]

Originally Posted by Purple Haze

Real submarines are faster underwater than on the surface.

In the performance formula from VE2, surface vessels with thrust above a certain threshold (based on what hydrodynamic lines they have) have increased top speed by hydroplaning. All of the stats I posted took advantage of that. Not sure how realistic that is though... I suspect the formula is much too generous.

[Phoenix_Dragon]

Originally Posted by Purple Haze

Real submarines are faster underwater than on the surface.

Modern submarines, yes. Older submarines, however, were more like boats that you could probably bring back up once you sunk them. They were designed primarily as surface ships, often lacking the capacity to stay underwater for more than a few hours, and were indeed faster on the surface than underwater (Though many older ones were also hindered by using different engines for surface and underwater propulsion). The modern hull design didn't appear until the 1950s. Considering the weird retro-tech strange-science of nautical lines on a spaceship, I suspect they're thinking the older-style design :>