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Old December 12th 05, 10:17 PM posted to rec.boats.cruising
rhys
 
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Default Boat Sank due to Syphoning Effect

On Mon, 12 Dec 2005 20:49:04 +0200, Mike the Spamkiller
wrote:


We usually open the toilet intake seacock when we get to our boat and
have it open as long as we are under way. Have reconsidered that
practice since then.


I draw lake water to flush through a seacock topped with a T-valve.
Above the T-valve (to the toilet and just a shave below the waterline)
is the drain hose to the sink. I leave the seacock SHUT unless I or
someone aboard is using the toilet. I have the option of emptying the
sink into the lake or if there's something noxious in the sink, I can
drain it into the toilet and then to the holding tank. This year, I
vented the loop as well. Everything is double-clamped. We've had two
boats sink at dock in a club of 220 in the last five years due to this
sort of issue...and it's completely avoidable.

The only seacock open when underway is the freshwater intake for the
motor. All others are shut unless in use. All others have bungs tied
to the seacock handles.

If you think of them not as seacocks but as "large holes in the bottom
of the boat capable of letting in dozens of gallons a minute" I find
it focuses the mind wonderfully.

R.

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Old December 12th 05, 11:10 PM posted to rec.boats.cruising
Lew Hodgett
 
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Default Vented loops

Subject

Vented loops are provided with a vent that functions like a "mechanical
ass hole", an engineering term introduced to me many years ago.

The vent allows flow in ONE direction only, just like a MAH.

Lew
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Old December 13th 05, 01:29 AM posted to rec.boats.cruising
Gary
 
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Default Boat Sank due to Syphoning Effect

phasmatis wrote:
A friend of mine has a Beneteau 345 moored in Corfu, it was due to be
lifted out for the winter this morning but unfortunately he had a phone
call from the Marina to say his boat had sank! The boat was stern on to
the pontoon and it was only the ropes holding the stern end out of the
water. There are no other boats on the pontoon as they have already
been lifted out.

The boat has now been pumped out and is afloat again and on inspection
there is no obvious reason why the boat would take on so much water to
sink the boat in a 12 hour period since it was last viewed.

The evening before the boat sank a large power craft powered at speed
through the Marina and created a very large bow wave, the only
explanation as to the cause that has been offered is that the bow wave
caused the toilet to overflow and created a syphoning effect which in
turn filled the yacht with water.

Anyone heard of this before?

Yup, my cousins bilge pump started syphoning and sank his boat.
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Old December 13th 05, 01:31 AM posted to rec.boats.cruising
Gary
 
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Default Boat Sank due to Syphoning Effect

Jeff wrote:
Peggie Hall wrote:
...

His toilet is below the waterline...I'd bet real money that a) he's
never installed a vented loop in the head intake...



Just curious - do most new boats come without the vented loop, or is
this caused by poor refits (or both)? Also, do the vents get clogged or
fail on their own? How often should they be cleaned out?

Thanks

Surveyors will look for the vented loops and note if they are not there.
Insurers require them. The need annual cleaning routines.

Gaz
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Old December 13th 05, 01:54 AM posted to rec.boats.cruising
Lauri Tarkkonen
 
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Default Boat Sank due to Syphoning Effect

In [email protected] Gary writes:

phasmatis wrote:
A friend of mine has a Beneteau 345 moored in Corfu, it was due to be
lifted out for the winter this morning but unfortunately he had a phone
call from the Marina to say his boat had sank! The boat was stern on to
the pontoon and it was only the ropes holding the stern end out of the
water. There are no other boats on the pontoon as they have already
been lifted out.

The boat has now been pumped out and is afloat again and on inspection
there is no obvious reason why the boat would take on so much water to
sink the boat in a 12 hour period since it was last viewed.

The evening before the boat sank a large power craft powered at speed
through the Marina and created a very large bow wave, the only
explanation as to the cause that has been offered is that the bow wave
caused the toilet to overflow and created a syphoning effect which in
turn filled the yacht with water.

Anyone heard of this before?

Yup, my cousins bilge pump started syphoning and sank his boat.


My neighbour in the club marina had a 30 footer, where the builder was
being smart and had joined the bilge pump and kitchen sink outlet. If
you left the kitchen sink plug on after you had pumped the bilge, you
had a perfect siphon. Of course it happened once. He was lucky that
someone noticed that hes freeboard (usually about six inches higher than
mine, was about a foot lower than mine and came to the rescue.

Another case was with the toalet pump in another boat. So if you make a
sifon, once it will work. Just wait long enough.

- Lauri Tarkkonen



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Old December 13th 05, 01:54 AM posted to rec.boats.cruising
Peggie Hall
 
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Default Boat Sank due to Syphoning Effect

Gary wrote:
Yup, my cousins bilge pump started syphoning and sank his boat.


I don' TEEENK that's what happened...for a couple of reasons: bilge
pumps don't bring water INTO the boat, they remove water FROM the
boat...and the thru-hulls for bilge pumps are above the waterline. So
unless there was already enough water in the boat to put the bilge pump
thru-hull under water, there's no way that a siphon can start in a bilge
pump line.

The water that sank your cousin's boat had to be coming in somewhere
else...and either the bilge pumps clogged and failed, or they kept
pumping till they drained the batteries and died...allowing the boat to
fill up and sink. Or, the water was coming in faster than the bilge
pumps could keep up with it. Or any combination/all of the above.

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1
http://shop.sailboatowners.com/books...ku=90&cat=1304
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Old December 13th 05, 02:36 AM posted to rec.boats.cruising
Stephen Trapani
 
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Default Boat Sank due to Syphoning Effect

Peggie Hall wrote:
phasmatis wrote:

The evening before the boat sank a large power craft powered at speed
through the Marina and created a very large bow wave, the only
explanation as to the cause that has been offered is that the bow wave
caused the toilet to overflow and created a syphoning effect which in
turn filled the yacht with water.
Anyone heard of this before?




Many times...but it's unlikely that the large wake had anything to do
with it. Head seacocks left open when no one is aboard are the leading
causes of boats sinking in their slips.

His toilet is below the waterline...I'd bet real money that a) he's
never installed a vented loop in the head intake...and b) he never
bothers to close the head intake (nor the discharge either) seacock when
he leaves the boat, foolishly relying on the wet/dry valve in the toilet
to prevent water from overflowing the bowl. Either the valve failed
(very common), or the toilet was left in the wet mode. It only takes a
few hours for enough water to flood the boat via the toilet to sink it.


So when I heard this last week here I realized I am one of the fools who
trusted their wet/dry valve and left the seacock open on the head
intake. I spent the last week trying to reassure myself that the wet/dry
valve has held up for a good year now (since I rebuilt the toilet!), but
I was nervous. So yesterday I finally got to the boat and closed the
seacock. Everything was dry as a bone on board. Just lucky I guess.

But my question is, I don't have a vented loop in the line, a vented
loop would be hardish to install with the layout I have. Should I put
one in or not, assuming I never again leave the seacock open?


--
Stephen

-------

For any proposition there is always some sufficiently narrow
interpretation of its terms, such that it turns out true, and
some sufficiently wide interpretation such that it turns out
false...concept stretching will refute *any* statement, and will
leave no true statement whatsoever.
-- Imre Lakatos
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Old December 13th 05, 03:17 AM posted to rec.boats.cruising
Peggie Hall
 
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Default Boat Sank due to Syphoning Effect

Stephen Trapani wrote:


So when I heard this last week here I realized I am one of the fools
who trusted their wet/dry valve and left the seacock open on the head
intake.


Not only the wet/dry valve, but also the last person to use the toilet
to leave it in the dry mode.

But my question is, I don't have a vented loop in the line, a vented
loop would be hardish to install with the layout I have. Should I
put one in or not, assuming I never again leave the seacock open?


Put one in. People are fallible...if you're only just beginning to
retrain yourself to close the seacocks, you WILL come in late enough and
and tired enough to say "to hell with the rest...it'll be ok this time."

Vented loops aren't quite 100% foolproof (you DO have to maintain 'em),
but they go a long way toward saving fools from ourselves, and they do
provide an arch in the line well above the waterline that water can't
rise above unless a siphon does get started.

Btw...the loop should be at least 6-8" above the waterline at ANY angle
of heel.

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1
http://shop.sailboatowners.com/books...ku=90&cat=1304
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Old December 13th 05, 03:24 AM posted to rec.boats.cruising
Peggie Hall
 
Posts: n/a
Default Boat Sank due to Syphoning Effect

Dave wrote:

On Tue, 13 Dec 2005 01:31:56 GMT, Gary said:


Surveyors will look for the vented loops and note if they are not there.
Insurers require them.



Not my experience.


You need to get to know a better clase of surveyors...REAL ones, not
just bozos who think that 10 years experience in doing things the wrong
way qualifies 'em call themselves a "surveyor."

Unfortunately, the same applies to insurance companies who don't know
that a boat isn't just a car or house that floats, or what a REAL
surveyor is supposed to know (and shouldn't even be IN the boat
insurance business--at least when it comes to anything bigger than a ski
boat)...so they hire the cheapest bozos and take their word for it that
the boat meets all the standards without ever bothering to find out
whether the bozo has the slightest idea WHAT standards, if any, apply.

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1
http://shop.sailboatowners.com/books...ku=90&cat=1304
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Old December 13th 05, 03:31 AM posted to rec.boats.cruising
Peggie Hall
 
Posts: n/a
Default Boat Sank due to Syphoning Effect

Lauri Tarkkonen wrote:
My neighbour in the club marina had a 30 footer, where the builder was
being smart and had joined the bilge pump and kitchen sink outlet. If
you left the kitchen sink plug on after you had pumped the bilge, you
had a perfect siphon.


You're saying that bilge pump discharged BELOW the waterline???? What
WAS the builder thinking??? Otoh, I had a consulting job last year on a
70' trawler on which both the gray water and the black water tank vents
terminated in charcoal canisters in the engine room, right next to a
propane furnace. So anything is possible.

Of course it happened once. He was lucky that
someone noticed that hes freeboard (usually about six inches higher than
mine, was about a foot lower than mine and came to the rescue.

Another case was with the toalet pump in another boat. So if you make a
sifon, once it will work. Just wait long enough.


But you CAN'T create a siphon if you close the bloomin' seacock! No
matter how inaccessible and inconvenient that may be, it's a whole LOT
easier and more convenient than drying out your boat after it's sunk in
its slip.
--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1
http://shop.sailboatowners.com/books...ku=90&cat=1304


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