Dust of Dryness and Sailing

[Afgncaap5]

I'm trying to determine what, if any, effect would come to pass if a person tossed Dust of Dryness off the side of a ship that was sailing across the ocean blue, and how/if the effect would change based on the amount of DoD used. Would the sudden removal of 15 cubic feet of water cause no effect on the nearby ship? Would it make a momentary "valley" of water that could potentially redirect the boat for a bit (ignoring effects of wind and/or competent sailors undoing said course change, of course)? Could enough of it create a potentially dangerous whirlpool-like effect?

Usually when I consider the effects of the Dust of Dryness I consider what the water is doing when the pellet breaks, but the potential application as a boat-course-corrector and/or story prompt for players to deal with is rattling around inside my skull.

[Chronos]

15 cubic feet isn't very much-- About 935 pounds. It'd be about the same magnitude of effect as four people cannonballing off the ship on the same side.

[bid]

You'd need 2 factors to evaluate the impact:
- what is the displacement of the the ship?
- what is the speed of the ship?

A schooner displacing 100 tons and 100 feet long will not be impacted by 5 feet / 0.5 ton of missing water.

[Afgncaap5]

15 cubic feet isn't very much-- About 935 pounds. It'd be about the same magnitude of effect as four people cannonballing off the ship on the same side.

Sounds like it might cause a mild disturbance to a canoe, though. I can work with that, especially with a crate of the stuff. Thanks!

[Ninja_Prawn]

A pinch of dust of dryness doesn't condense 15 cuft of water. It condenses a cube, 15 feet to a side. That's 3,375 cuft, and suddenly losing that volume probably would cause enough disturbance to be felt on the deck of a decent-size warship.

Still though. The amount of water moving around when the seas are rough and stormy is enormous. If a ship can withstand those kind of forces, I doubt your magic dust will give it too much trouble.

[Monster Manuel]

It can have an impact if it's the RIGHT 15 foot cube, though.

Displacing 15' of water right at the bow will cause the ship to dip, but no more than it would going over a 15-foot swell, which happens all the time. But, in the middle of a calm sea when the crew isn't expecting it? I'd give you a chance to give them a reasonably easy dex save or stumble.

Where it can be really nasty, though, is if a ship is passing just over some barrier, like a reef or sand bar. That quick 15-foot dip has a much bigger impact if it ends up with the keel colliding with a barrier reef at speed. It will fill in momentarily, lifting the ship back up, so it won't be stuck. But that sudden impact could do damage, will DEFINITELY knock the crew around and possibly overboard, and it will take some time for the ship to get going again.

Of course, if you use the stuff on board the ship, inside the ship's stores, destroying 15 cubic feet of their drinking water, barring magical aid in replenishing it, could be really catastrophic in the long term. I've used that as leverage on a pirate ship in a Pathfinder campaign, where Create Water was a cantrip. "The bad news is, I've destroyed all of your drinking water and you're 6 days out from the nearest port. The good news is that I can cast Create Water at will, and will happily play quartermaster for the rest of the trip in exchange for passage to skullport and 10% of your take..."

Not exactly shipwreck-in-a-bag, but still fun.

[Grey Watcher]

It can have an impact if it's the RIGHT 15 foot cube, though.

Displacing 15' of water right at the bow will cause the ship to dip, but no more than it would going over a 15-foot swell, which happens all the time. But, in the middle of a calm sea when the crew isn't expecting it? I'd give you a chance to give them a reasonably easy dex save or stumble.

Where it can be really nasty, though, is if a ship is passing just over some barrier, like a reef or sand bar. That quick 15-foot dip has a much bigger impact if it ends up with the keel colliding with a barrier reef at speed. It will fill in momentarily, lifting the ship back up, so it won't be stuck. But that sudden impact could do damage, will DEFINITELY knock the crew around and possibly overboard, and it will take some time for the ship to get going again.

Of course, if you use the stuff on board the ship, inside the ship's stores, destroying 15 cubic feet of their drinking water, barring magical aid in replenishing it, could be really catastrophic in the long term. I've used that as leverage on a pirate ship in a Pathfinder campaign, where Create Water was a cantrip. "The bad news is, I've destroyed all of your drinking water and you're 6 days out from the nearest port. The good news is that I can cast Create Water at will, and will happily play quartermaster for the rest of the trip in exchange for passage to skullport and 10% of your take..."

Not exactly shipwreck-in-a-bag, but still fun.

If you get super lucky, the damage to the hull might be enough to punch a hole in it. Bonus points if the pellet created by the dust gets smashed between the ship and whatever it just grounded on. Probably more of an icing on the cake thing, but if it ends up in exactly the right (or wrong) place, that extra sploosh has some fun potential as well.

[MrStabby]

Right behind a ship would cause a massive differential in pressure that would bring a ship to a sharp stop. Couple this with some strong tailwind and you could be snapping some masts.

Of interest might be the other side. Take a long metal tube, closed at one end. Drop the marble of water from the dust to the bottom, drop a metal ball on top to crush it and you have a water powered cannon or mortar. Or drop the party gnome in the tube to stamp on it if you want to launch an airborne assault on a ship.

[da newt]

I'm sure there are people who can actually figure out exactly what the effect would be, but I don't know the right physics / engineering, however:

a 15*15*15 ft cube of water is 3375 cubic ft and weighs 210,600 lbs or ~ 105 tons per pinch of dust

an average 50 ton ship is 40-60' long depending on construction (according to the interwebs)

A ship is not designed to be supported only by the bow and stern (removing the water in the middle), and the real damage comes from the surrounding water crashing back in to fill the void (100+ tons of water accelerating at around 9.8 m/s2 is a bunch of force and water doesn't compress)

Torpedoes are often designed to explode under the hull of a ship rather than on contact because the explosive force under the keel (pushing water away) and then the force of water rushing back in to fill the void causes more damage than a direct hit.

The real question is how quickly does the dust work? If it's instantaneous, this is HUGE, if it takes 10 seconds you might not notice it at all.

[Chronos]

The middle being unsupported, while the bow and stern were raised on large waves, was also what caused the wreck of the Edmund Fitzgerald.