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Old 21-08-2012, 15:46   #46
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Re: Sinking ??????

In your first paragraph you square the diameter of the hole, which is correct, when you write the equation you forgot the square, and you do your calc without the square.

So your example is actually 360 GPM.

The original example at a 3 inch hole at 120 GPM will be at 0.6 feet below the waterline.


Quote:
Originally Posted by GordMay View Post
The volume of water that enters a boat is proportional to the square root of the depth of the hole and proportional to the square of the hole’s radius. That is, a hole twice as deep allows in 1.4 times more water, and a hole twice as large lets in four times more water.

Incoming gallons per minute = D x square root of H x 20
where
D = the diameter of the hole in inches
H = depth of the hole below outside water level*

Hence: A 3 inch diameter hole, 4 feet below the waterline will let in 120 gallons a minute, or 7,200 gallons an hour. (Mr. B's 3" hole would have to more than 4 ft. down)

Most boats don’t (cannot) have a bilge pump system which is large enough to keep up with a leak caused by hull damage. Bilge pumps are designed for small quantities of water, and are not damage control pumps.

See ➥ http://www.uscgboating.org/assets/1/...g/News/251.PDF

* However, the flooding rate of a boat will slow down considerably when the water level rises above the leak. In this case, the “h” in the flooding formula becomes the difference in level between the water inside the hull and the water outside it. Additionally, any air in the cabin will provide back-pressure to further slow the flow.


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Old 21-08-2012, 23:54   #47
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Re: Sinking ??????

The point that GordMay albeit corrected by Cal40john is absolutely right,, if there is hull damage causing an influx to such a great extent then no bilge pump able to be carried aboard is going to cope.

In this instance you have 3 chances:-
1) Block the hole with a Pillow/Doona/Small dog anything that will stem the flow to enable your pumps to cope. This is more important initially than all other actions.
2) Compartmentalise your boat, difficult unless at design phase or unless your designer was on the ball.
3) Pray.

Under Australian USL Code guidelines for ship/boat construction watertight compartments with isolation procedures must be a part of all commercial vessels construction.

It saddened me when the 'Day Charter Industry' wormed their way around regulations to enable, at the time, the Whitsunday area 'RENTA A YACHT' businesses to thrive.

In essence 'exemption to preventing sinking' was given because it was just too hard to apply to small boats, probably same happened in other parts of the world.

It would have been fruitful for designers to be enforced to reduce the risk by compartmenting the underbody, watertight bunk bases with hatches etc.

Today most production boats have both cable and piping runs go from one end of the boat to the other in the bilge area with very few glands.

Second job we did on our 'new to us cat' was to seal all bulkhead penetrations so at least we have a fore and aft watertight.

Also remeber the old saying 'NO BILGE PUMP IS AS GOOD AS A SCARED MAN WITH A BUCKET'..... Cheers
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Old 22-08-2012, 07:05   #48
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Re: sinking??????

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Originally Posted by micah719 View Post
Myth? Perhaps...I'll dig in my cellar one of these days, I'm certain I have the book I'm thinking it was in. From what I remember he had it hearsay as well. If it ran into the bilge I can only imagine a nasty mess, but if it dripped continuously on the one spot I assume it could eat a hole. Maybe something to experiment with to see if it works. Mythbusters?
Probably not with polyester resin... I've soaked my roller in acetone for 3 weeks b/c I forgot to clean it immediately... The acetone didn't phase it once it was kicked... Maybe some of the early polymers wouldn't stand up to it, but I doubt it would eat through the glass with today's stuff. Works great for clean up if it hasn't kicked yet, though!
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Old 22-08-2012, 07:07   #49
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Re: sinking??????

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Originally Posted by gonesail View Post
funny thing about the hose clamps: i have removed hoses from thru hulls and can assure you that it is not an easy task. sometimes the hose must be cut just to get it off the bronze fitting. more often it must be muscled off with great strength. the odds of one of those hoses coming off by itself? remote to impossible
I had the same experience replacing my hoses. Had to cut them off. If they were just installed though.... without proper hose clamps, all it would take is a bump from something loose in the bilge.
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Old 22-08-2012, 09:42   #50
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Re: Sinking ??????

cal40john:
Thanks for the correction (again).
Gord

Quote:
Originally Posted by cal40john View Post
In your first paragraph you square the diameter of the hole, which is correct, when you write the equation you forgot the square, and you do your calc without the square.

So your example is actually 360 GPM.

The original example at a 3 inch hole at 120 GPM will be at 0.6 feet below the waterline.
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Old 22-08-2012, 17:15   #51
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Re: sinking??????

Quote:
Originally Posted by micah719 View Post
Myth? Perhaps...I'll dig in my cellar one of these days, I'm certain I have the book I'm thinking it was in. From what I remember he had it hearsay as well. If it ran into the bilge I can only imagine a nasty mess, but if it dripped continuously on the one spot I assume it could eat a hole. Maybe something to experiment with to see if it works. Mythbusters?
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Originally Posted by micah719 View Post
I read a story once about a GRP boat sinking because someone left a bottle of nail-varnish remover (acetone) open in the heads compartment: it tipped over, leaked into the bildge, ate a hole in the hull and sank it. I'm fairly sure it was in a book by Peter Kemp.
This one smacks of pure urban legend status. Acetone will not dissolve cured polyester resin, epoxy or fibreglass.

OTOH, an acquaintance of mine had a boat sink at the dock (San Leandro CA marina) from an acetone spill. He had unwisely used Tygon (Clear, unreinforced PVC) hose for his cockpit drains. He failed to notice that while he had cleaned up the acetone that he saw on the cockpit sole, quite a lot must have gone into the drain where it sat and eventually destroyed the hose.

So, from all the stories above, it is clear that not only is a boat is a hole in the water into which you throw all your money, that hole wants to fill itself with water as well. Beware!

Cheers,

Jim
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Old 22-08-2012, 17:18   #52
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Re: sinking??????

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Originally Posted by Jim Cate View Post

So, from all the stories above, it is clear that not only is a boat is a hole in the water into which you throw all your money, that hole wants to fill itself with water as well. Beware!

Cheers,

Jim
Nature abhors a vacuum.

If you don't throw money in that hole it will likely fill with water...
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Old 22-08-2012, 17:45   #53
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Re: Sinking ??????

The acetone story is hard to believe if for no other reason then acetone evaporates very quickly. I'd think there would be more chance of it causing an explosion then dissolving cured polyester, Ethanol apparently can dissolve some polyester resins given enough time if reports of damage to fibreglass tanks holding fuels with ethanol content are to be believed.

And having just paid for replacement hoses and clamps to replace my cockpit drain and bilge pump hoses, I'm thinking it would be cheaper to let the boat sink lol.
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Old 23-08-2012, 16:05   #54
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Re: sinking??????

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Originally Posted by mbianka View Post
When I was sailing on the 88 foot schooner Ocean Star a number of years ago there were always two of us on watch during the night. One of those people had to do a "boat check" every hour. They would walk through all the compartments
including the engine room with a flashlight checking for something amiss. Including checking the bilge. Seems like a good practice on any boat.
I have a bilge alarm installed; a little float in a chamber that rings an alarm if the water pushes the float up. Even with that, I flashlight the bilge every day and underway every hour or two. It really doesn't take all that long and is cheap insurance.
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