"Geyser" produces 30 gallons of water that gushes forth in a geyser 30 feet long and 1 foot wide. As a bonus action while holding the decanter, you can aim the geyser at a creature you can see within 30 feet of you. The target must succeed on a DC 13 Strength saving throw or take 1d4 bludgeoning damage and fall prone. Instead of a creature, you can target an object that isn't being worn or carried and that weighs no more than 200 pounds. The object is either knocked over or pushed up to 15 feet away from you.
Probably not a lot, remember that this is its force against an object, not its force against the Air. You wouldn't be able to build a rocket ship with this because you'd run out of matter to push against. Although if your DM approves you might be able to use it to make a bottle rocket of size.
so your asking if you can do this ?
30 gallons of water would be gone really quickly...I don't think you can maintain that spray for more than a turn/one action. 30'x1'x'1 (assume a narrow cone/cylinder...) It's a single blast, not unlike a plunger-style squirt gun, but with the strength (because: MAGIC!) of a modern firehose.
So, my question is, does this magic item produce and expel 30 gal per sec? per round? per turn? Just once a day when you use it like this?
I mean, if it will produce 30 gal/sec at velosity high enough to shoot 30' and move 200 lbs... FOR EVER....I'd find a way to power something with it. A ship, a water mill, anything. Or just create a lake over a year or so....You got something to allow your PC to retire from all that dangerous adventuring crap. Heck, you could even transform desert into farmland given enough time and this item. 
PS: that video clip is so X-TREEM ...I feel like a frat boy who just beer-bonged Red Bull and Smirnoff 100 with a gaggle of vapid bakini babes while yelling F***-YEAH BRAH!
Yunru wrote:
Engineering and D&D magic are basically two mutually exclusive sciences tbh
That being said; to calculate the power excerted by the decanter you will need to access the speed at which the water leaves the "muzzle". One way to do this would be to decide what is mean by the 30 feet range. Maybe the 30 feet range is where the beam of water has lost 1m in height? Under that assumption you could calculate the required exit velocity to create this ballistic trajectory and then the excerted reverse force.
My gut feeling: Way more than 889N.
In Dark Sun/Athas it works much differently.
Well I assumed 30 ft straight up, because then you've reduced the variables, but what do I know?
Last night I was thinking of how the decanter could otherwise be used, and instead of trying to hover, or use a golem turning a crank like I mentioned earlier, just have the decanter move a water wheel. This means you could have it power a mill for grinding grain or cutting wood, lift and lower something at a speed inversely proportional to the mass, or any other task that converts torque to your needs. Could also use it in a water tower with no need to pump the water, or use the decanter to pump resevoir water into the tower, and have running water in a city.
kalil wrote:
Oriet wrote:
But that's where your wrong. Even if magic prevents an equal reaction, that's still a method of propulsion: Attach the Decanter to a system such that the water hits another part of the system. That interaction obeys phsyics, generating a forward momentum.
Yunru wrote:
You can push a 200lb object 15'.
So... assuming a 0.5 cooefficent, you can push a 200lbs object 7.5' up.
Note that there is no "kickback", from this. So you need to blast yourself.
mellored wrote:
It's just as Yunru said. We know the effects of the stream of water hitting an object, as it's specified in the description for pushing creatures and objects. Having it mounted somewhere stationary and using the geyser to push paddles on a water wheel is no different than someone pointing it at and pushing a statue, cart, or dead kobold. That it doesn't push back on the creature or object holding it makes it even simpler to mount, as you just need it held and not braced. If it also ignores more mundane physics like gravity and equilibrium then you get even more utility out of it as it then doesn't matter what direction you point it in to harness energy from the stream of water.
You see, that's the beauty of the stated effects: you know how it behaves in specific situations. All you then have to do is set up those situations of known effects and alter the target properties (like a paddle wheel instead of a crate) to convert that energy (in this case water pressure into torque). Even if you have to use a water wheel that weighs no more than 200 lbs for the geyser to rotate it, or where the whole of the system/device cannot exceed the energy requirement of moving 200 lbs 15' a round, you can still put it to some application.
Yunru wrote:
The biggest issue is going to be repeating the command word every 6 seconds ... wonder if you could cast a variation of Magic Mouth to trigger it?
If there is no "kickback," can I just hold the decanter, pointed at myself without letting go, and use it to fly backwards indefinitely in any direction dependent on how I angle it? Perpetual motion!
Creatures do not get shoved. Only knocked prone. Only objects get shoved.
ChrisCarlson wrote:
Timborama wrote:
ChrisCarlson wrote:
As a DM, if you pointed it at yourself, the last thing I would be inclined to do is let you attempt a saving throw...
ChrisCarlson wrote:
Pompadour64 wrote:
Yunru wrote:
Assuming there's not permanent sources of heat with which to boil said water?
A spell/magic item that can provide a lot of heat, such as to make a magically powered stove, would be incredibly useful, even if virtually useless in combat by itself. Whether it's just a plate, rod, or other shape of metal or a magical flame that produces a bit of heat doesn't matter, so long as you can use it to boil water. Combine that with a magical water source like the decanter and you can make small steam eninges, as the biggest problem with them is having enough water and fuel to last for some time and to generate enough power to move all of that fuel and water along with what you actually want to move. A magical heat source would also allow for hot air balloons, and with a steam powered propeller you can make a blimp; or add a frame and make a rigid body airship for even better maneuverability.
Whether you can get the above or not, a spell or magic item that simply rotates would also be of great utility for the same reasons, but without the need to make steam.
And suddenly I have an explanation as to why the gnomes in my universe are very steampunky on their floating island...
It's easy to see how D&D can have a world with steam powered carriages, airships, and other machinery and still have no (or very little) gunpowder or other "modern" contrivances. It's quite fascinating, really. Such items might be in the cost of the airship listed on page 119 of the DMG, unless it uses mundane means of lift and propulsion.
In our current homebrew campaign, mountain dwarves live on massive earth motes floating in the sky. Because of this, they created sky ships unique to the setting. Rather than go with traditional "lighter-than-air" or whathaveyou, being dwarves, I decided they instead harness the floating stone from their homes. But in order to make the massive, solid stones "blimps" move, they had to team up with their nearby steampunk gnome kin to develop tech that can direct the otherwise inirtially-resistant floating rock. Steam-powered engines channel electro-magnetic energy through a series of massive iron rods inserted through the massive chunks of earth mote. This allows the pilot to trick the stone into "falling" in a desired direction by changing it's gravity.
ChrisCarlson wrote: