i got no maths for it, but i am VERY interested in the physics of this.

Namely, having say 4-6 of these bonded to the back of the ship like thruster rockets

File: 1352157359731.png-(486 KB, 800x1000, darksouls3.png)

Bump.

>having an conduit to elemental plane of water
>using it as a reaction engine

in short term, I'd say it's horribly inefficient use of magical energy. In long term it's just plain stupid, because what are you going to do about all that water?

File: 1352157548372.jpg-(239 KB, 2338x1700, CALCULATIONS!.jpg)

980 lbs of force. The calculations in the picture.

>>21448009
>>lbs
>>force
nigga what?

>>21448134
Pounds are a measure of force. Kilograms are a measure of mass. learn the difference before being stupid on the internet. If you want it changed into Newtons, do the calculation yourself.

>>21448188
This. Btw, i fail to find anything to compare it with.

>>21448134
The pound is the unit of force. I think you are the ignorant one, here. Unless you prefer the metric system, which is understandable.

>>21448223

Newtons are the standard SI unit too, but yeah the conversion calculations are easy, so stop trying to find reasons to be butthurt on the internet, >>21448134 At least he included units.

>>21448009
Why on earth would you use imperial?

>>21448259
Cause it's better?
It's not based on "ok, here's a 1, what can we say this 1 is? X atoms wide"?

>>21448259


Because 'Murica!

Also, that is the units that the book uses for volume of water and flow rate.

>>21448218
The math gets very tricky immediately in regards to how quickly it could propel your boat, because we don't know (and I'm pretty sure you don't know) how hydrodynamic your boat is. I have no experience in this kind of thing. But if you were to just throw out a number, we could determine a maximum speed (the speed at which the resistance of the ocean is equal to the force of the decanter) and then, for the sake of simplicity, say that the ship accelerates to maybe 1/10th of that speed per round.

>>21448259
>>21448289
>>21448295
coming from a 'murrican: no idea. The only measurement I prefer in imperial is farenheit over celcius, because it uses smaller increments and is therefore more precise. Even so, that's no reason to be incredulous when someone uses pounds as their unit.

>>21448259
>>21448134
>>21448188
>>21448257

I used imperial because everything was already in gallons and feet.

The answer in 4360 Newtons if you want that instead.

>>21448218
>>21448303
Imagine five 200lb neckbeards are standing on the back of your boat, and gravity is horizontal for them. tadah, there's your reference!

>>21448289

Basing it on three arrow lengths is better? the atoms wide thing is an after the fact thing anyway, for the meter at least. It was originally1 ten millionth the distance between the Equator and the North Pole.

>>21448327

Rankine?

And why wouldn't that guy use lbs anyway, all the information given was in feet and gallons. There's less fractions to keep track of converting at the end rather than immediately.

Lets ignore the unwashed masses and presume it's a dnd sailing ship and just calm water, no need to go into details.

File: 1352159340499.jpg-(32 KB, 550x384, PB1168[1].jpg)

So, this question is actually asked fairly often, it seems. A quick Google search on 'thrust in 30 gallons per 6 seconds" lead me to three different forums, all discussing this.

Now, one of the main downsides to using a Decanter of Endless Water is the whole 'endless water' bit - every time you run your engine, you're adding more water to the ocean / river / lake / world in question. So, you might want to specify the water is coming out of the ocean during creation, unless your GM isn't going to punish you for this by flooding all the little coastal towns and villages.

Anyway, it would seem you'd be better off using Fabricate, Hardening, Permanence, Wall of Stone, and Wall of Magma to make yourself a steam engine.

First, make a large open cylinder out of the Wall of Stone spell. Wall of Magma will adhere to the Wall of Stone, as per the spell description. So, use Harding on the Wall of Stone, so the Wall of Magma can never melt it, and line the cylinder with the Wall of Magma. Same for the Decanter - harden it, then put it inside the Magma. Fabricate the boiler out of steel, and harden it. Place decanter assembly inside boiler, fabricate outlet pipes into rear of the ship, below water line, and viola - on command, jets of steam billow forth to scoot your ship from hither and yon.

You could also rig an actual steam piston engine, if you'd rather, and use that to provide locomotion via paddle wheels or a propeller. Your call.

Here's a pastebin with the most relevant steam engine discussion.
http://pastebin.com/jeBeNkL4

How heavy is your boat OP? And how big a cargo can you put in it (weight)?

>>21448303
It is a Longship, I am guessing viking style if that can help.

>>21448455

Now, one of the main downsides to using a Decanter of Endless Water is the whole 'endless water' bit - every time you run your engine, you're adding more water to the ocean / river / lake / world in question. So, you might want to specify the water is coming out of the ocean during creation, unless your GM isn't going to punish you for this by flooding all the little coastal towns and villages.

I realy don`t think the amount of water produced has a impact on a ocean, you would need to keep that thing running for a crazy long time to have a mesurable effect

>>21448548
If you feel this will have an impact then look at how much the poles melt and refreeze every year,

http://www.youtube.com/watch?v=CVHArJa5LX8

>>21448455
at first I was skeptical of this; the world is huge, I doubted one ship could do enough to meaningfully alter sea level.

I was right.

One ship running this engine continually would take eight billion years to raise the global sea level ten meters, which was my metric for what would be disastrous for many coastal villages.

You can run this all you like, OP. Even share it with friends. Nobody's going to notice.

>>21448682
>One ship running this engine continually would take eight billion years to raise the global sea level ten meters, which was my metric for what would be disastrous for many coastal villages.

source?

>>21448756
Basic algebra and googled units.

>>21448007
they are in the ocean.

>>21448009

Thank you, my good sir! It is much appreciated.

>>21448682
>ten meters, which was my metric for what would be disastrous for many coastal villages
Shit, dude, 10m is loads. Half a meter would be fairly awful for a lot of people. That would still take an insanely long time but still.

>>21449003
http://en.wikipedia.org/wiki/Current_sea_level_rise

It is happening you know.

In dnd the might be spheres of anailation and shit hidden in the sea eating up water for all we know.

>>21449135
It could just sit on the surface. That would mean that as the sea level rose past a certain point, water would get sucked in and it would remain normalized. That's assuming you're not set on an enormous flat world.

>>21449168
Tg, fixing global flooding.

>>21449189
Through use of dangerous magical artifacts.

>>21449274
Naturally!

Glad to see I wasn't the only one concerned with potential pretend coastal flooding.

I only brought it up because I've had GM's who would punish the players for something like that. The whole 'disruption of the ecosystem' and all that. But hey, I'm not about to do all the math to see exactly how long it would take to have a single decanter of Endless Water fill an ocean. I just think that introducing 2 million gallons of water into any body of water after a full month of operation time is a significant volume. And that's as far as I went with the maths.

File: 1352164090329.jpg-(41 KB, 499x341, 1338997444754.jpg)

>>21448762
>I'm going to be a cunt and instead of throwing the actual math at you I'll just say I did math.

>>21448455
Just because you turned liquid water into a gas does not mean you are not moving more matter into that environment.

>>21448007
Dump it in some fairy's castle?

Now we need to figure out the drag induced by 980 pounds of force. And I am in no way going to do this, because fuck aerodynamics

>>21449189
Spheres of Annihilation at great depth. At the surface it would be ineffective as the water would not be destroyed fast enough (gallons per second most likely) however a few miles down and the pressure would be shoving tens of tons of super dense water into it per second.

>>21449512
>Wizard straps Decanter of Endless water to back
>Wizard uses Decanter of Endless water as a god damn jetpack
>The Druid, now disgruntled that it cannot smack the Wizard around for fucking the environment all manners of over sends the piranhas up stream.

>>21449474
Might I suggest that you compare that number to the number of gallons of water there are in the ocean to begin with?

Trillion gallons/square mile
325 million square miles

Now I'm not going to say that we shouldn't worry, but it's not as cut and dry as your number in isolation suggests.

>>21449533
If you're going to go to THAT much trouble, you might as well just set up a gate to the elemental plane of water that periodically measures changes in the amount of water in the world and opens long enough to dump any excess back into it, if there is any.

But again, it would take an unbelievable shitton of people using these things to make ANY kind of impact, much less a significant or even noticeable one.

>>21449496
I did state in that post 'you might want to specify the water is coming out of the ocean during creation', as in [Your world's ocean] and [creation of the Decanter of Endless Water']. That way you're just cycling existing water from point A to Point B, instead of adding water in from the Elemental Plane of Water or some such. There's nothing stopping you from doing that during item creation, as far as i know. Most people just link them to the Elemental Plane of Water because said plane is full of pure, fresh water - good for drinking.

>>21449505
Pffft. I'd post that screen cap, but I saw it already up on /tg/ in another thread.

>>21449545
I did ask google how many gallons of water were in the ocean, and then tried to divide that by 7200 (Gallons created per hour at 30 gallons per 6 seconds [1 turn]) but gave up after the Google calculator started giving me letters and +19 at the end. I do not do integers, or whatever they're called. I'm an English major (or at least, I was).

>>21449474
Dude.

There are appoximately 1,101,117,147,428.57 (slightly over A QUADRILLION) gallons of water in a SINGLE cubic mile.

Assuming a decanter at full blast produces 1 million gallons of water, it would have to run uninterrupted for for 1 million months to put out enough water to fill a cubic mile. 1 million months is 83,333.33 years.

The PCs aren't going to affect a motherfucking thing even if they're using a thousand decanters at full blast 24/7.

>>21449512
100-150 ton boat pushed by 980lb thrust? I can tell you right now that it's not going to move very fast.

Plugged it into gurps vehicles and you'd need about 25 of them just to match what sails would give on a light breeze. Sails are very efficient at what they do.

Good if you want to move on a windless day, but then longships have oars and a crew of 50 to use them? 9000 gold for the decanter, crew of 50 is 5gp a day. So at 1 silver piece a day you could pay the crew for 1800 days or about 5 years. For 25 decanters to actually move the ship at a reasonable 10mph rate you could pay the crew for 123 years.

>>21449638
> Assuming a decanter at full blast produces 1 million gallons of water

I left the words "per month" off the end of that, I apologize.

>>21449656
Yes, but MOTHERFUCKIN' WIZARDS

>>21449656
Longboats aren't that heavy though. I'd figure 10 tons.
A shallow-draft, cabinless boat, no more than 100 feet long? Not 100 tons.

If the water from the Decanter was freshwater, which would pose an ecological problem first: desalinisation, or sea level rise?

If the water addition is being countered by Spheres of Destruction, desalinisation will be a problem eventually. When you have a mass extinction of ocean life, that releases a lot of greenhouse gasses and prevents sequestering...

>>21449700
Sorry but no. Displacement is 70 to 100 tons. The standard D&D ones carries 120 soldiers 50 tons cargo.

It's not a rowboat.

>>21449751
Actually, that's a thought. Could you place a sphere of annihilation in FRONT of the ship, so that the water moving might drag the ship forwards slightly? Balance it right and you should be able to remove the water from the oceans at about the same rate it's going in, and get a small boost to the ship's speed in the process

>>21449753
I see, you were referring to displacement, not weight.

Back to the question of speed:

F=ma
mass of a longship is roughly 20 tons or 18,000 Kg

a = (4360 - Force of friction)/18,000 = acceleration in meters per second squared.

I don't know how to figure out the friction due to the water and air for a viking longboat because I lack those coefficients of kinetic friction or other opposing forces for moving in water. If friction is 0, acceleration = decanters X .24 m/s/s.

So from rest it accelerates to about 2.4 m/sec in 10 seconds with 1 decanter, or roughly 5 miles per hour. Opposing forces probably cap the speed at about 8 miles per hour, which is decently fast for a boat. Each extra decanter is probably about 2/3-3/4 more effective, so 2 would get you going about 14 mph, 3 about 18 mph, 4 about 21 mph, 5 about 23 mph.

That's my best approximation.

>>21449889
That's pretty good for an engine you never have to maintain, refuel, or fix.

What if you strapped another one on?

>>21449542
that is awesome totally gonna have to do that with my next wizard.

>>21449925
>>21449889
Pretty good, except he figures water to be frictionless and the mass of a boat that carries up to 200 people and and or 50 tons of cargo to be 20 tons total.

It's a very optimistic estimate.

>>21447676
Don't fucking bother with the naval propulsion aspect.

1. Acquire a bonded fire elemental or other source of unlimited heat.

2. Construct a pressure vessel (i.e. a big spherical airtight tank) and a nozzle.

3. Direct the geyser into the pressure vessel, apply heat.

4. INFINITE STEAM ROCKET.

Don't bother running an ocean ship. Build a goddamn spaceship. Because you don't have to carry your reaction mass with you (it gets pulled out of the Elemental Plane of Water), you completely avoid the difficulties of most rockets.

A calculation on LoP's old Dirty Tricks threads says that just one Decanter, built like this, will give you half the thrust of the Space Shuttle's main engine- with none of the extra weight from those fuckhuge fuel tanks. Three decanters should be enough to turn your ship into a goddamned Spelljammer.

>>21450143
But yeah, a straight Decanter isn't going to get you much thrust, as the various calculations in this thread have shown. Add some heat, though...

>>21450176
Actually, let me run the actual numbers instead of relying on somebody else. To make things simple, let's say that the boiler chamber has to be made out of Adamantine or Riverrine or some other unbreakable material. How much of that would be reasonable for you to afford, OP?

>>21450236
Here's the equations I'm using:
http://www.grc.nasa.gov/WWW/k-12/airplane/rktthsum.html

>>21449968

Screw doing it with a wizard, do it with an artificer and turn the decanters into FLUDD from Mario Sunshine.

An easier way of going about doing things... One of my own devising that allows for practically infinite speed on tap of any sort of vessel, albeit somewhat expensive towards the top end of things.

Step 1.
Make a Lightning Turbine (Arms and equipment).

Step 2.
Construct a sealing cylinder that one end of the turbine can be inserted with slightly larger capacity than is needed for the ooze it will contain. (This is to allow someone on watch the ability to pump air into the "engine" as needed).

Step 3.
Harden the cylinder and turbine to adequate levels to withstand full on maximized, twinned, etc etc nastiest Lightning Bolt you think you'll see.

Step 4.
Shove a living Lightning Bolt spell into one end, screw in the turbine and attach to the vehicle of choice.

How it works:
Living spells are oozes and the fluff/rules specifically state Living Spells do not need food since they draw upon the ambient magical energies in the air. Since lightning is what drives the turbine, anything engulfed by a living spell is affected by the spell it's based on automatically.

The first of these contraptions will give the vehicle a speed of 90 feet/round OR twice the speed of the vehicle (whichever is greater). Each one after that doubles the speed until you can quite easily get to relativistic speeds and beyond.

All said and done you can probably (with judicious hardening spells) make a complete "engine" for less than 500 lbs. Even if weight were an issue, a single Enveloping Pit (MIC) should provide all the extra space/weight carrying you need for the entirety of the engines easily.

Alright, so after doing some heavily back-of-the-envelope, guesstimatey calculations, a steam rocket with a DoEW on full blast as reaction mass and a way to heat that up to the typical operating temperatures of steam engines would put out about 27 kN of thrust.

Plugging that value into >>21449889 's heavily optimistic calculations gives me an acceleration of 1.5 m/s/s for a 20-ton vessel, assuming no friction.

That means that, if it were a frictionless environment, in just ten seconds you'd accelerate to 33 mph. Two decanters would get you up to 66 mph in that time.

>>21451285
That is blazing fast for a longboat.

>>21451285
And, after some very rough calculations on top speed, you should get something like 200 mph as your top speed with one decanter. Two will get you up to 400 mph.

So: Ordinary decanters are meh propulsion devices. Don't bother buying that third decanter; spend that money on some glyphs of water to steam or a Brazier of Endless Fire or something and some copper plumbing.

>>21451467
Also, if you somehow manage to save up for seven decanters, you'll have enough thrust to perform VTOL in your longboat.

>>21451467
What. That is fucking insane.

Also, it's a wooden boat. Wouldn't the stress tear the whole thing apart without enormous reinforcing?

>>21451548
Yes, if you add too many decanters or turn the heat and force up too high the engine is going to punch out of its anchor points and tear through the hull like a giant bullet.

>>21451588
But there's something so gratifying about building an engine so powerful that it tears out of your ship and blasts through it like a steam-powered rocket.

>>21451611

Also, mount a pair of decanter-boilers on your ship with long piping on the end. With an exhaust velocity of approximately FUCKLOTS meters per second, you ought to be able to do some serious damage using those as steam cannons.