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Tramp Freighters underwater
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cheshire
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PostPosted: Thu Feb 25, 2021 10:40 am    Post subject: Reply with quote

Just eyeballing some crush depths of submarines, I would suggest that each 50 meters of depth does 1D of damage to the hull. A solid 4D hull, could *maybe* be safe at 200 meters (competitive with WW2 Uboats), and shrug off the pressure. Something that is specially designed like the Deepwater should have more flexibility, though I don't think I have a mechanic for that.
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Whill
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PostPosted: Thu Feb 25, 2021 3:54 pm    Post subject: Reply with quote

cheshire wrote:
Just eyeballing some crush depths of submarines, I would suggest that each 50 meters of depth does 1D of damage to the hull. A solid 4D hull, could *maybe* be safe at 200 meters (competitive with WW2 Uboats), and shrug off the pressure. Something that is specially designed like the Deepwater should have more flexibility, though I don't think I have a mechanic for that.

Thanks. The DeepWater comes with a rule in RAW. The stats indicate a special underwater shields mode that protects the ship and comes with a max depth (1 km).

The question was mainly for spaceships without a specially designed hull or special shield mode, which could also apply to the DeepWater when the shields aren't functional.

I was going to go with 1D of damage per 100m of depth, but this seems more reasonable. Thanks again.
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PostPosted: Sat Mar 06, 2021 8:17 pm    Post subject: Spaceships Underwater Reply with quote

I've reread this thread and thought about the cheshire's suggestion. In the debates we've had over the years about spaceship hulls dealing with external pressure, it has been argued that most spaceships are designed to hold atmosphere in when the ship is flying in the vacuum of space, not maintain integrity versus external pressure. While I agree that most spaceships are not specifically designed to survive underwater, I have argued that spaceships are designed for more than just holding an atmosphere in. Even commercial spaceship hulls are also designed to withstand several other external forces, such as high pressure from high speed atmospheric travel, asteroid strikes, pirate attacks, and the physics-defying ravages of lightspeed transitions and hyperspace travel. That means they should therefore be able to withstand some degree of water pressure.

As shown in the films and other media, sublight drives can function in vacuums and atmospheres. But I feel they should not be able to function underwater. Aquatic ships have separate subaqueous drives. A non-aquatic spaceship can only travel underwater using its repulsorlift drive, probably at a low speed since it is primarily used to maneuver slowly for landings and take-offs. This use of repulsorlift drives would allow most spaceships to be able to land on the solid bottom of a body of water if the depth wasn't too deep for the ship to survive the water pressure.

Sublight drives were designed to survive atmospheres, space, and hyperspace without letting anything outside of the ships in, and without letting any air inside the ships out. Luke's X-Wing was submerged on Dagobah and it still worked afterward (and a robot functioned underwater), so I feel that even for non-aquatic spaceships, the sublight drives would not be damaged or ruined just by going underwater to a safe depth. Trying to use the sublight engines underwater would likely damage them (which could create a hull breach leading to more damage), but if they are off when going underwater, the sublight drive should be fine. I would imagine that if the sublight engines were just shut down right before going underwater they would be very hot and cause a lost of steam to bubble to the surface, which could be a problem for a bit if trying to hide from a close pursuer. I also think it is quite reasonable for a GM to rule that shut down sublight engines may not be immediately usable when first coming out of water, so they may need time to drain or dry out first. For aquatic spaceships, the sublight drive still can't be used underwater but can be used immediately after rising to the surface.

Energy shields on non-aquatic spaceships do not work at all underwater so cannot be used. The Deepwater's shields have a special mode to protect against water pressure, which as a side effect also provides very minimal additional physical damage protection. On the MC-13v2, shields have a special mode that creates a supercavitation effect allowing a faster speed but no protection. On both ships, the normal protection shield mode is not available underwater. And although particle shields are considered to be part of the hull stat, I decided to not worry about that for the underwater pressure chart/rule. Maybe particle shields do maintain some degree of function underwater since water is composed of physical particles.


So I categorize all spaceships into three categories with respect to underwater travel or survival:

. . (1) Spaceships with no special attributes for underwater survival (most all spaceships)
. . (2) Aquatic spaceships with a special shield mode for underwater survival (i.e. the DeepWater-class)
. . (3) Aquatic spaceships with hulls especially designed to withstand underwater depths (i.e. the MC-13v2)

The following mostly addresses starship-scale ships of category (1) and (2) when the shields are not functional. As a base, this is for earthlike planets with the same gravity and sea level as Earth. Different planets may adjust this...

cheshire wrote:
Just eyeballing some crush depths of submarines, I would suggest that each 50 meters of depth does 1D of damage to the hull. A solid 4D hull, could *maybe* be safe at 200 meters (competitive with WW2 Uboats), and shrug off the pressure.

The DeepWater does not have a mechanic per se (dice rolling). It just indicates a rule that a DeepWater with functioning shields (which can convert to underwater mode) has a max depth of 1 km. (It does not give rules for going deeper or for what happens if the shields fail, so those situations are left to the GM.) I'd like to have a similar underwater pressure rule (no roll until a certain depth) for ships not designed for underwater use or ships like the Deepwater when the shields fail (or for aquatic ships going beyond their limit).

For the guideline I've decided to round up your "maybe" to this: Spaceships can withstand water pressure at a depth of 50m for every 1D of hull, and 15m for every pip. If going deeper, then damage rolls begin every round with the hull resisting a water pressure damage according to the same formula. See the chart below, which is used to both determine the safe depth (without rolling for damage) and the damage code when exceeding it.

015m - 0D+1
030m - 0D+2
050m - 1D
065m - 1D+1
080m - 1D+2
100m - 2D
115m - 2D+1
130m - 2D+2
150m - 3D
165m - 3D+1
180m - 3D+2
200m - 4D
215m - 4D+1
230m - 4D+2
250m - 5D
265m - 5D+1
280m - 5D+2
300m - 6D
315m - 6D+1
330m - 6D+2
350m - 7D
365m - 7D+1
380m - 7D+2
400m - 8D
415m - 8D+1
430m - 8D+2
450m - 9D
465m - 9D+1
480m - 9D+2
500m - 10D
500m+ - 10D+

Of course the lower end of this chart would normally only apply to a DeepWater that gets its shields damaged while underwater and suddenly finds itself below a safe depth (which is exactly why the MC-13v2 does not depend on special shields to survive the pressures of the deep). For depths more than 500m, just use the difference in meters to determine the difference in die code added to 10D damage. The max safe depth of the DeepWater (with fully functional shields) and the MC-13v2 is 1 km, so I would also use this chart if they ventured below that depth, by just taking the distance beyond 1 km deep, and adding the corresponding die code to the ship's hull code for the damage code to be rolled against the hull code.



And since I could not find any thread devoted to submarines in general, I thought I would just mention here that I created a new submarine and posted it here.
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