Decanter Of Endless Water Math [Archive] - Giant in the Playground Forums

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TypoNinja

2012-11-26, 07:19 PM

So the decanter, I was looking at it, and realized the math on it seems weak.

Decanter of Endless Water

If the stopper is removed from this ordinary-looking flask and a command word spoken, an amount of fresh or salt water pours out. Separate command words determine the type as well as the volume and velocity.

"Stream" pours out 1 gallon per round.
"Fountain" produces a 5-foot-long stream at 5 gallons per round.
"Geyser" produces a 20-foot-long, 1-foot-wide stream at 30 gallons per round.

The geyser effect causes considerable back pressure, requiring the holder to make a DC 12 Strength check to avoid being knocked down. The force of the geyser deals 1d4 points of damage but can only affect one target per round. The command word must be spoken to stop it.

A 1 foot wide stream that produces 5 Gallons a second, is a pretty low flow rate in terms of use against a person. Sure it blows away your bathtub in terms of volume, but that 1 foot wide stream is what kills it as a weapon.

Unless I've flubbed the math, the water coming out of a decanter on geyser mode is moving at a hair over 3.4 MPH, only a little over walking speed.

Cog

2012-11-26, 07:27 PM

Perhaps it's a hollow stream, basically a ring in cross-section instead of a full circle?

The Random NPC

2012-11-26, 07:31 PM

Not only that, at 30 gallons a round, it takes about 6 rounds to fill up a coffin sized area. So not a lot of water coming out of it.

Seer_of_Heart

2012-11-26, 09:27 PM

Yep this is weird, time to do some math!

Assuming they mean that geyser releases the water in a cylindrical form that cylinder would have an area of about 31.4 cubic feet. Some googling tells me that, 31.4 cubic feet is about 234.9 gallons. The actual flow is 30 gallons, but the expected amount is ~7.8 times as much. Meaning that either 87.3% of the geyser is what came out of the decanter last round, or the water is mistlike and takes up 12.7% of the air in the area of the geyser.

Darth Stabber

2012-11-26, 10:02 PM

Not only that, at 30 gallons a round, it takes about 6 rounds to fill up a coffin sized area. So not a lot of water coming out of it.

Filling a coffin in under a minute is actually a pretty impressive rate for things that aren't riot water cannons.

TopCheese

2012-11-26, 11:17 PM

TypoNinja

2012-11-27, 01:05 AM

I'm sleepy but bare with me...

30 gallom/ 6 seconds = 5 gallons a second....

Think about getting hit by 5 gallons of water every second...

It is also hitting you pretty fast... 20 feet long in 6 seconds = 3.xx feet/second

The water is travaling at a speed of 3.00 (rounded down) feet / second and every second you are getting hit by 5 gallons.

1 gallon = 8lbs thus 5 gallons = 40lbs/second at a velocity of 3 ft/second

40lbs traveling at about 1.4 miles/hr hitting you constantly... Ouch

That's my point, the math doesn't add up. 5 gallons a second out of a 1 foot diameter opening is not going to give you a 20 foot stream, you can jog faster than the water will be moving.

The stated flow rate, does not come close to providing the stated distance of a stream, or the force equivalent of a dc 12 strength check.

Its the huge diameter that kills it. A fire-hose has a diameter of 1.25 inches, water cannons for crowd control have diameters in fractions of inches to get high pressure across dozens of feet.

ericgrau

2012-11-27, 01:09 AM

It's probably only 1 foot wide at the end of the 20 feet. At the start it's still only flask sized, which probably means an opening of around 1/2" to 1".

The Random NPC

2012-11-27, 07:20 AM

Filling a coffin in under a minute is actually a pretty impressive rate for things that aren't riot water cannons.

Now that I think about it, it does seem pretty fast. I did my math about a year ago to figure out how much water Dust of Dryness took up, now that is a disappointing item.