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tjdono
03-17-2003, 09:55 PM
As I get ready to refit the plumbing on Lady Nola, which has 2 heads, three sinks, and a shower, my sick mind contemplates the worst. If a pipe fitting breaks loose under shorewater pressure, how long under 40psi would it take to sink my 42' motoryacht? She displaces 21,000. Also, the original system, which seeps in many places, is copper. I am contemplating replacement with PVC and CPVC or the cross-linked polymer tubing. Any caveats or suggestions??

Scott Rosen
03-17-2003, 10:03 PM
Turn the shore water off whenever you leave the boat.

Bob Cleek
03-17-2003, 11:15 PM
Gee, Scott... what a novel idea! I was about to say, how long it would take to sink the boat at 40 PSI really depends on how big the pipe is! No? Probably the best way to find out is to disconnect the suspect fitting and turn the hose up full blast and then stand by with a stopwatch. If it takes too long, you could tie the stopwatch to the rail and go fish for it the next day. When it stopped would give you a pretty good idea of how long it took to sink the boat!

Bob Cleek
03-17-2003, 11:24 PM
PS to Tom Jackson: Now that you've got the watch Specter used to have, maybe you should pick the "Forum Question of the Month" for inclusion in your section of WB. It would be good for a few laughs!

PPS to Tjdono... sorry for the humor at your expense. I realize it is not really a stupid question... I mean, the part about how long it would take might be, but... never mind. Anyhow, I have had the same concern on a motor home rig and the answer is that IF ALL PARTS of the plumbing system are in good shape (not leaking, etc.) and rated for the shore pressure applied, there should be no problem. BUT, as things have a way of letting go when you least expect it, the better practice, seriously now, is to follow Scott's advice. Don't leave the system under pressure when you aren't aboard. (This includes the electric pressure pump as well, although if a pipe let go, you wouldn't have any more water in the boat than was in your tanks to begin with, which cannot sink the boat, but can make a mess... not to mention the cost of a burned out pressure pump.) If the plumbing system is properly constructed and maintained, you should have no greater worry than you would about your house flooding if a pipe burst, and when was the last time you worried about that? BUT, an ounce of prevention is worth a pound of salvage charges!

Bruce Hooke
03-17-2003, 11:35 PM
Calculating how many hours it would take is going to be difficult because it depends on the size of the pipe, the nature of the break, and the freeboard and displacement of the boat, among other things. However, I would hazard a guess that under the most likely scenerios we are talking quite a few hours, but probably less than a day (unless there was a good bilge pump sending the water right on overboard, in which case it might never sink, unless the electricity went out). That said, even if it took a day, unless someone is going to be on board all the time the boat could easily sink before anyone noticed. Say the break took place mid-day, on a stormy, rainy day. If nobody were paying close attention it might not be noticed before dark, and by the time someone was around the next morning it could be too late, or at least a lot of damage might have been done. So, if at all possible I would follow Scott and Bob's advice and plan to turn off the water when you leave the boat. If you plan things right this shouldn't be hard to do. Just throw one valve and be done with it. That is unless there are things on board that for some reason need a water supply even when you are not on board.

John B
03-18-2003, 12:11 AM
we sailed into our moorings one day and Kirsty made a rude remark about the "push me pull you" boat. On closer inspection it was a motorsailer ... 40 ft or so, down by the bow and with about 18 in of bow freeboard. Being a young fool, I got aboard and went below through the forehatch into knee deep water. The head was fountaining , syphoning fast and I blocked it with a mop. I got on deck to check the freeboard and when I went back down I went aft to look for other seacocks and the mop blew out of the toilet.
There was one of those moments.
I looked around, the water was nearer my waist than the knee, it was a steel boat and the washboards were steel and locked.I thought F this.
I got out. there was only about 6 in of bow freeboard left .We watched it for another 15 minutes and she went to the bottom.

Getting on it was stupid even though driven by a desire to be helpful. I had no hope of finding the real reason for it sinking... the head was syphoning because it was left open plus the boat had sunk that low to cause the syphon.
It turned out to be a deck wash fitting in the bow which had let go.
why do I tell you this? I don't know how long it took. Probably a day until she hit the syphon point, then a few hours at the most.
Seacocks should be turned off when you leave a boat.IMO.
This is true. I count it as being in my " stupid things I have done" file

Wiley Baggins
03-18-2003, 12:26 AM
Now that (John B's story) should be in the column, steel boat, or no.

D
03-18-2003, 07:37 AM
I would probably shy away from CPVC. It is very hard and very brittle. You would be better off sticking with copper.

Dan McCosh
03-18-2003, 08:55 AM
This reminds me of one of my father's dictums that he would never have shore water on a boat, after seeing one so equipped sink at the dock. He also never trusted hydraulic shift levers after seeing one ram a dock; and always used a separate grounding chain while refueling.

As for the question--the main factor is how low it sinks before a really big opening goes under water, such as the exhaust pipe. Also, most of the damage from flooding comes well before the boat actually sinks, in terms of oil floating around from a submerged engine, etc. Don't ask how I know.

Dan McCosh
03-18-2003, 09:08 AM
This reminds me of one of my father's dictums that he would never have shore water on a boat, after seeing one so equipped sink at the dock. He also never trusted hydraulic shift levers after seeing one ram a dock; and always used a separate grounding chain while refueling.

As for the question--the main factor is how low it sinks before a really big opening goes under water, such as the exhaust pipe. Also, most of the damage from flooding comes well before the boat actually sinks, in terms of oil floating around from a submerged engine, etc. Don't ask how I know.

Matt J.
03-18-2003, 09:49 AM
I have a book by H. Herreshoff at home (a little yellow “handbook” of sailing, or some such name). In the book the times to sink an average vessel w/o bilge pumps working if holed for different size holes are listed. I seem to recall even a small diameter hole of about 1” diameter took a matter of minutes… as for 40 psi… I will pull out the old reference books on lunch and crunch some numbers. How much water would sink the boat? Any guesses? How much by weight or volume? That I don’t know, but the numbers I can crunch.

For a large hole (I want to say a 5” diameter hole) the sinking tie was VERY low – I’m thinking under a minute :eek: .

Matt

High C
03-18-2003, 11:03 AM
I can fill my 450 gallon 6 man (uhh, make that 3 men and 3 women) hot tub in about 45 minutes with a 5/8" garden hose. It wouldn't take long at that rate to sink a boat if something let loose.

Close those thru hulls, and shut off those valves and pumps when you're away! My boat is right here at the house where I can see it, and I still take these precautions.

Nicholas Carey
03-18-2003, 01:29 PM
Originally posted by tjdono:
As I get ready to refit the plumbing on Lady Nola...my sick mind contemplates the worst. If a pipe fitting breaks loose under shorewater pressure, how long under 40psi would it take to sink my 42' motoryacht? She displaces 21,000.Well, pulling out my handy-dandy

http://www.sequoiapublishing.com/images/cov_pocketref3.jpg (http://www.sequoiapublishing.com/pdt_pocketref3ed.htm)

And looking up the nozzle discharge tables, we find that at 40psi, a 1-inch diameter nozzle's theoretical discharge rate is 189 gallons per minute. Actual flow should be about 95% of that, or about 180 gallons per minute.

Water weighs 8.35 pounds per gallon, so you'd be losing bouyancy at a rate of about 1,500 pounds per minute.

How long she'll take before sinking depends on how much reserve bouyancy she has and how stable she is, especially considering the free surface effect of all that water.

Just for the sake of argument, if you figure she has...oh...40,000 pounds of reserve bouyancy, it'll take about 27 minutes for her to sink, assuming she's stable.

Joebob sez...shut down the shore water when not aboard.

John B
03-18-2003, 03:28 PM
I regularly remove my log for cleaning. It's impeller body is about 1 1/2 in diam approx.
I don't know what 40 psi looks like but it sounds like a lot to me . That impeller hole generates a head ( a wee fountain)of about a foot when it's out. I can't imagine it being anywhere near 40 psi. 2 or 5 perhaps.

Nicholas Carey
03-18-2003, 03:52 PM
Originally posted by John B:
I regularly remove my log for cleaning. It's impeller body is about 1 1/2 in diam approx.
I don't know what 40 psi looks like but it sounds like a lot to me . That impeller hole generates a head ( a wee fountain)of about a foot when it's out. I can't imagine it being anywhere near 40 psi. 2 or 5 perhaps.Right, but he's talking about a broken pipe bringing city water into the boat. And he specified 40psi. He may know what the water pressure in the pipe is.

videoguy
03-18-2003, 05:16 PM
Why would anyone leave their boat for any length of time with the waterpresure on . We even shut of the water to the washing mach when we will be gone for more than a few hours. :confused: ...Phil

John B
03-18-2003, 06:36 PM
gotcha. :rolleyes: I missed the significance of that.I've never heard of doing that actually.

[ 03-18-2003, 06:37 PM: Message edited by: John B ]

tjdono
03-18-2003, 09:44 PM
Hey Guys!
Wrote the oringinal post here last night...got up..went to work..came home....and laughed my ass off reading the first few threads! Thanks Mr. Cleek, et al! Now, when I leave my boat, my intention is always to shut down city water. I have forgotten once, about a week ago and drove the 25 miles back to shut her off. That incident, plus the impending plumbing refit, is what prompted this thread. To answer the last few guys...I have a pressure reducer installed inline to limit pressure coming in to 40 psi. Its a 5/8 hose for supply. I have twin 125 gal monel tanks for the house water underway pressurized with a PAR pump. I could simply 86 the city system but like the convenience and freshness, of the city system as well. So there you have it, I was thrilled to see such a plethora of activity on my little thread!
Thanks again
Tim

Bob Adams
03-19-2003, 12:17 AM
I just run off my tank. That way if something goes, you only have water in the bilge whose weight was already accounted for anyway. Leaving city water hooked up is absolutely bad news.