Engineering question (speed of water ingress)

Hi folks,
three of us went sailing this afternoon in the South Pugent Sound with an uncharacteristicly constant 12 knot wind, when someone came up with an interesting topic for discussion:
"a thru hull seacock 4 feet below the waterline is left open...the water coming into the boat has a certain amount of pressure, and will produce a gusher that rises a certain height...is it possible to calculate the volume and height of the water comming into the boat if the hole is known to be 1 inch? Part two: Now the waterfilled boat is lifted out of the water... would it drain slower, or at the same rate, from the hole? Why or why not? (we are a carpenter, an internet system engineer, and an avionics technician, all three sheets to the wind)

By my calculation, water will come in faster than it drains out. Approximately 16.5 psi pushing it in vs. 14.7 psi pushing it out. I'm too thirsty to figure out the height of the fountain.

I need to go buy some beer.

Hmmmm, very interesting....why would it be different?

What kind of beer?
What is the basis for 16.5 psi?
And 14.5 psi ?
inquiring minds want to know...

The hole that is letting the water in is below the level of the sea. Sea level water pressure is 14.7lbs (1 bar) on an absolute gage, and as one goes down below the surface, water pressure increases.

Iny or Outy?

Not only is the pressure different, you've got the weight of the boat "above" the waterline. When breached the flow would be the highest. As the boat sinks the pressure would equalize, but you're still going down!

Upon salvage there would only be the weight of the water to consider.

As far as the height of the "geyser", this can only be determined w/ a field test. A qualified technician(the carpenter) should measure the resultant "geyser" w/ a suitable measuring device. My initial thought is that the "geyser" would rise to the approximate level of the surrounding water.

Gravity

My favorite is Redhook ESB, if it's fresh (less than a month old) and has been stored cool most its bottled life. Redhook's ales are bottled cold and should be kept cold, for longest shelf life.

Gravity is the culprit. Our atmosphere is miles and miles thick and gravity pulls all that air down towards the surface, where it presses on us, at sea level, with about 14.7 pounds per square inch of pressure. Water is heavier than air* and it only takes a depth of 33 feet of water to make 14.7 pounds per square inch pressure. Four feet of water exerts about 1.78 pounds per square inch (4/33 x 14.7).

The reason you add the water induced pressure to the air pressure is because the air is also pressing down on the water surface. It all adds up as you continue going downwards. When a diver goes down 33 feet, for example, he has 2 x 14.7 psi or 29.4 psi (two atmospheres) of pressure on his/her body. It's an ear popping experience.

*Disclosure: Actually water molecules are more massive than air molecules and therefore gravity makes 33 feet of water weigh as much as miles and miles of air. I'm and engineer, not a physicist, so the professors among us can take it from here.

Aha! that makes sense now. OK, so the height of the fountain of water coming in a 1 inch hole would depend on the angle of entry, but would be acted on by the force of gravity in any case, so we know it's not going to rise 4 feet even if vertical...(I am guessing the height would be slightly less than two feet, or half the depth, accounting for friction loss) The volume of water is the bonus question. Anyone?
I enjoy Hales Mongoose , and Pyramid Thunderhead IPA's, but in the old days, (before RH sold out ), I was an ESB fan.

It was a bittersweet day for me when A-B bought a piece of Redhook. But, I was pleased to find that the additional brewery in Conn. meant that ESB showed up in unexpected places - like a grocery store in Knox, Indiana. It was fresh and cold and you have no idea how nice it was to find it there. The taste and quality seem to be un-affected by their affiliation with A-B.

Of course, I remember the days when Coors wasn't found very far east of the Colorado state line. The good old days. We could/should start a beer/ale and alcoholic beverage thread in the Lifestyle Forum. We could deal with important questions there, such as "How high does a 12 oz. longneck bottle of Coors squirt after you shake it?" and "What beer should the beer connoisseur drink while performing these tests?"

Great thread, Dave. Thanks for the opportunity to expound.

Knox, Indiana reference: No slight intended there. My folks and and a whole bunch of my cousins were born very near by and most still live around there.

Talk to the Navy!

The process to answer your question is actually very easy! That being said, I don't remember the equations needed to plug in numbers. Since your in the Seattle, Washington, call one of the Navy ships in the area and ask to speak to the Damage Control Assistant. It his (or her) job to know how much water will come into the ship from a certain size hole located a certain distance below the waterline.

I am lost where does Tequila fit in this equation?

This is how I remember it

You can call a seacock a simple orifice or nozzle. Flow will be affected by the shape and restrictions, but generally the flow can be predicted by taking the square root of the depth of water, times 19.636 x the diameter squared of the opening. To pin it down further you should times by a friction coefficient based on restrictions, anywhere from 0.98 to 0.50. I would split at 0.75 to be realistic.

for example: say the depth is 3.5 feet with a 1-1/4" sea cock, then the flow would be about 43 gallons per minute.

or the original post asked about: 4 feet depth with a 1" seacock, then the flow would be about 29.5 gallons per minute.



Steve
e35-3 #159

Now were talking. (OK, the Margueritas can be served now...no salt, thanks)
Does this rate of flow remain constant as the vessel sinks? Or does it increase, at a rate proportionate to the increasing depth/pressure?

Wow, thirty gallons per minute (give or take) from a 1 inch hole. Gives one pause for sobering thought.

Think of that long and twisted bilge pump hose run

Here's another fact of life that will make you drink! (more)

There is a good chance that your bilge pump won't even make a dent or keep up due to flow loss from the hose restrictions. These pump ratings are very deceiving, it might say 1500 GPH but that's without any hoses attached. Add a pick-up hose and a long run discharge plus elevation and you now have 750 GPH. Some surveyors say anywhere between 3,000 and 4,500 GPH is recommended to be safe... wow!

Add additional pump(s) with as short a hose run as practical. I haven't tried this, it might make some sense. -Some day while at the dock, open a sea cock to the sea -that won't ruin anything nearby, and see if the pump(s) can keep up. You'll know quickly, long before it washes over the sole. Really, how else can you be sure!

Keeping around those wooden plugs takes on a whole different meaning.

Steve

Big numbers

30 gal per minute x 60 minutes = 1800 gal per hour

What's the volume of a boat?

Thanks, Steve.

Doesn't the inflow slow down? As she sinks, the hole goes lower in the water (which would increase the pressure and therefore the inflow) but the water table in the boat rises faster (for a flaired hull shape) - so the fluid head gets lower and the rate of incoming water drops.

For the boat out of the water, if full to level of 4 feet, initial drain rate is same. But the drain rate slows down as the water level in the boat drops.

By the way, I'm a bit rusty on the math, but assuming a 0.75 coef friction and negligible air friction, I get the initial height of the fountain of 2.24 feet =
4 ft head x sq of coef friction (I think - any engineers know for sure?)

"a thru hull seacock 4 feet below the waterline is left open...the water coming into the boat has a certain amount of pressure, and will produce a gusher that rises a certain height...is it possible to calculate the volume and height of the water comming into the boat if the hole is known to be 1 inch? Part two: Now the waterfilled boat is lifted out of the water... would it drain slower, or at the same rate, from the hole? Why or why not?

A better question: is this a TRICK question?

First, an open seacock isn't necessarily an invitation to water intrusion. As a matter of fact, I can think of several examples where closed seacocks would cause real heartburn. Or rather - burning of one's engine. So, the question SHOULD be:

"A hose blows off a seackock below the water line. How long will it take before the boat sinks, and/or the bilge pump gives up the ghost?"

Second issue: the notion a waterfilled boat is 'lifted out of the water.' I'm no Archimedes, but I'd surmise a waterfilled boat would go the other direction.*

I hope this sheds some light on the problem.

*PS: Okay, I'm being a smartass. I realize you meant to say: 'when a boat is HAULED (lifted in slings) out of the water.

Capt Dan G>E35II "Kunu"

I for one am a rather simple guy and don't drink (which strangely does seem to have some importance here) I do have the mental horsepower to do the math, at least in theory, but prefer to just keep the water out! When it starts to come in stop it! While it may be a fun exercise to measure the height of the pretty fountain.... it is an expensive show. and once in, the answer to the question of how fast it will drain, is always not fast enough! The real scary part of this thread is that when you add in the volume of that water and subtract it from the volume inside the boat it shows how quickly the damage will add up. It hill pickle an engine in a few minutes, then attack the woodwork, the electronics, the ... and will leave mold mildew and rot just to leave a lasting impression. I don't mean to be a wet blanket on this thread but on the other hand, have you checked all those hoses, clamps and thru hulls lately?...sure? OK now it"s Miller time

I too (like all of us I'm sure) am paranoid of every hole in the boat. Is it possible to get rid of (at least some of) them? Depth sounder can work through the hull. How about the knotmeter - anything on the market that uses ultrasound or something. Can I flush the head from a fresh water holding tank? Is it possible to air cool an engine? and what about the scuppers - two huge holes in the bottom just to drain the cockpit - is there an alternative?

The best defense is a good offense, but not if you are talking about the Detroit Lions!!
This thread shows why it is imperative to have top quality thru-hulls, seacocks, and marine grade double clamped hoses. It is also a very good habit to close all seacocks when not on board. Insurance companies get quite upset when a claim is filed for a vessel that has sunken at the docks because of a defective hose or thru-hull fitting. We use a "buddy system" where I keep my Ericson, meaning that everyone looks out for vessels that are not sitting on their lines, or just don't look right in the water. It's amazing how fast an owner will get to his boat when he is called because the boat is lower in the water !!