# Leaking holding tank causes boat to almost sink?



## davidpm (Oct 22, 2007)

This thread http://www.sailnet.com/forums/boat-review-purchase-forum/61936-buyer-beware-3.html mentions that a holding tank leaking caused a boat to fill up with a lot of water because of reverse siphoning.

I can almost visualize a holding tank springing a leak that as the water leaked out caused a vacuum that could pull water in from outside, but not quite.

Where exactly would it pull in the seawater?
The head is between the tank and the raw water inlet.
The massarator outlet would have a shut off through-hull on it, plus a pump.

The tank would have a vent that would not allow a vacuum to build up in any event.

Sucking the wast out with a pump out station would cause more vacuum than any leak in any event.

So exactly what combination of events could have happened to cause the problem reported.


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## Architeuthis (Mar 3, 2008)

In my system, which I designed so blame no one, the tank itself is below the water line. The hose from the thruhull to the pump (and then tank) is also below the water line. It is that 1" hose that would need a anti-syphon. As it is the seawater can leak by the pump, slowly but it does and then fills the tank. 

In my case the hose from the head is a bit higher and seems to be just above the waterline but I would expect the seawater to fill that hose as well. 

So with the valve left open the only thing preventing the boat from sinking is the hoses and fittings connected to the tank, the tank itself and the valve at the toilet which is not designed for that so I would expect it to leak or fail first. A failure of any of those items that result in water coming in at a rate higher than the pumps pump it out gives Davy another ship.

If the 1" hose from the mac pump was to rise to an anti-syphon device all that could be avoided. 

BTW when I bought the boat the thruhull was left open. The tank was full. It was an old aluminum tank and I found a spot so weak I could break thru the tank with my thumb. That is all that kept the boat afloat (if the pump had failed).


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## mitiempo (Sep 19, 2008)

I think in a properly installed system if the below the waterline through hull was left open the holding tank would fill with water but as long as the hoses were still attached to their connections that is all that would happen. There should be 2 anti-siphons installed for a conventional head. The first should be between the pump and the back of the bowl. The second should be in the outlet hose between the bowl and the holding tank. If this is done the water that enters the holding tank from the open through hull cannot siphon past the holding tank into the head itself. An anti-siphon is not required between the holding tank and through hull and in most under V-berth installations is impractical as well.
On the other hand if there is not an anti-siphon between the bowl and the holding tank the boat could flood if the through hull was left open. The solution is to install one.


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## Architeuthis (Mar 3, 2008)

Or keep the valve closed. As you suggest there is not a one size fits all solution which is why there are so many differences. 

So many differences that I'm not sure what is conventional. It seems conventional has only one hose to the thruhull, from the mac pump? Thats what I did in part because it seemed to be the most common. 

The older style, which seems to be so old that most of them have been changed over the years had the head connected to the thruhull, some had tanks some did not. 

And then there are other differences, depending on boat. At one point ours had a Y valve going to the thruhull which I think had a single anti-syphon because that is all that style would need. 

And there are newer ones that have no thruhull at all. I think that is because they are required in some areas. 

I like to keep the ocean out of my boat as much as possible so would not be comfortable counting on a tank and it's hoses. Though I might if I had designed it for that. 

Speaking of keeping the ocean out the thruhull for the sink drains seem to be a poor idea. It looks like the only purpose is to avoid having to clean a sump.


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## mitiempo (Sep 19, 2008)

With a conventional pump head I know of no safe install that doesn't have 2 anti-siphons installed. One from pump to bowl and one on the outlet. Of course if the through hulls are ALWAYS closed when the head is not in use there is no problem, but how often does that happen. I have no problem with a through hull as long as it is properly installed, has 2 good hose clamps on quality hose and has an anti-siphon installed where required.


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## davidpm (Oct 22, 2007)

This is a Wooden Boat Graphic

http://i321.photobucket.com/albums/nn367/davidm203/head.jpg


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## mitiempo (Sep 19, 2008)

That is almost right, but the intake anti-siphon should be in the line from the pump to the bowl, not in the hose from the inlet to the pump. The hose from pump to bowl isn't shown in that diagram.


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## southerncross31 (Sep 16, 2006)

The safest setup for a holding tank system is also the easiest to use. Step 1: get a Lavac toilet. Step 2: install a holding tank above the waterline. The intake hose for the toilet is looped above the waterline with an anti siphon valve. The outlet from the toilet goes directly into the holding tank (no outlet to the water) from the top of the tank. There is a typical breather from the tank. The tank then has an outlet at the bottom which is connected to a y valve. One side goes to a drainage seacock, the other to the pumpout fitting on deck. With this system there is no way for the water to backflow unless the tank is already under water (in which case the toilet is the least of your worries! The lavac toilets have no joker valve. Instead they rely on a vacuum created by a henderson bilge pump. NO clogs....ever!!!! It goes like this. Poop....then close the lid with a seal on it. Pump the pump 5-6 times and the water will be pulled into the bowl...crap goes out and into the holding tank as the bowl is re-filled. Simple.....nothing breaks and the crap is macerated by the big pump. Again, there are no small valves to be clogged and there is no direct path for water back-flow. Now the real advantage to this system is this; Say you have been in and out of harbors...... cruising for several weeks.. your tank is full and there are no pumpouts. All you do is turn the y-valve ( 3 miles out) and the tank will gravity drain (and wash itself out). Again, it is not possible for the water to backflow into the tank or the toilet! I installed this system on my SC 31 and it worked flawlessly!!! To bad i was forced to sell the boat . Now my Oday 25 c/b has a portable toilet....yeah......no more thru-hulls at all! At least i'm still on the water...in April that is.... and i'm not taking this boat offshore!


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## mitiempo (Sep 19, 2008)

I agree the Lavac is the best solution. This is what I have on my boat (my previous posts were for Jabsco type heads). I will also be installing a gravity drain holding tank across from the head in the back of the large hanging locker. But I disagree with the Y valve below the tank. In my to be built tank there will be a drain at the tank bottom directly to a through hull with seacock. The deck pumpout will come from the top of the tank and will be directly above the bottom drain. There are several advantages to this. One, there is no Y valve which requires 3 additional connections that are possible leak issues. Two, if by slim chance the drain clogs just open the deck pumpout fitting and as it is above the drain a rod pushed down will clear the clog. I have the inlet hose looped to just under the deck with the Lavac supplied vent at the high point. The outlet line goes from the pump to a anti-siphon fitting also just under the deck then down, across and up to the top of the gravity tank. There will be a vent on the holding tank of course.


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## davidpm (Oct 22, 2007)

mitiempo said:


> That is almost right, but the intake anti-siphon should be in the line from the pump to the bowl, not in the hose from the inlet to the pump. The hose from pump to bowl isn't shown in that diagram.


In fact Jabsco specifically says it is wrong to put the loop in the inlet side.
Apparently it will not even work as the pump will just suck air.

http://www.myboatsgear.com/newsletter/images/jabsco vented loop.pdf


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## davidpm (Oct 22, 2007)

How about this drawing?
Plumbing Diagram For Marine Head - Toilet Plumbing Diagram Cruisers & Sailing Photo Gallery

Or this one

http://i321.photobucket.com/albums/nn367/davidm203/head5.jpg
From How Boat Things Work


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## Maine Sail (Jan 6, 2003)

mitiempo said:


> With a conventional pump head I know of no safe install that doesn't have 2 anti-siphons installed. One from pump to bowl and one on the outlet. Of course if the through hulls are ALWAYS closed when the head is not in use there is no problem, but how often does that happen. I have no problem with a through hull as long as it is properly installed, has 2 good hose clamps on quality hose and has an anti-siphon installed where required.


ABYC standards also call for this so all new boats built to ABYC standards have this set up. Many boats have sunk due to poor head plumbing. Just check in with Peggy Hall over on SBO and you'll get a lot of stories..

Siphon events are more common than most think and the head can not be counted on as a valve so you need vacuum breakers to prevent siphoning. Relying solely on a seacock, and a human to always shut it, can become quite risky.

Of course there are some heads like the old Groco model K and the WC Skipper models where you can't put a siphon break between the pump and back of the bowl because flush water is routed internally. In this case a siphon break on the intake and a finger over the vent hole while pumping can work. I have seen a valve on top of the siphon break but again this can be forgotten, a finger plugging the siphon break can not..

Vented loops/siphon breaks, should be placed in the pressure side of a pump, not the intake side, unless there is NO other option. This is why you need the finger tip method to plug it as I mentioned above. A Lavac pump can often overcome the incoming air from the siphon break but small Jabsco Head Mate etc. pumps most often can't and you just suck air and get horrible flushing performance.

The vented loop should be placed between the head pump outlet and the bowl inlet (under pressure) by removing the small factory plastic hose that leads from the pump output around the back of the bowl and replacing it with the high point and vented loop if you have a head where you can do this. This is a very common mistake people make, installing a vented loop on an intake line.

Vented loops/siphon breaks let air into a standing column of water, under the vacuum created by the weight of the standing water in the hoses, to break a siphon. They also allow air into the system while pumping, if place on the suction side, thus reducing performance. This is why they are not intended to be used on a suction line. They seal on pressure, break on vacuum/suction.

This is such a misunderstood product that I have even seen some boat yards install them on the suction side of a raw water pump. Doh' !!! The pump can eventually over come the incoming air, and will move water, but often has dry periods and short impeller & pump life. Not a good situation..


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## sailingdog (Mar 19, 2006)

Actually, I'd point out that the LAVAC requires a siphon break on the intake line as part of its installation IIRC.


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## davidpm (Oct 22, 2007)

Maine Sail said:


> ABYC standards also call for this so all new boats built to ABYC standards have this set up. Many boats have sunk due to poor head plumbing. Just check in with Peggy Hall over on SBO and you'll get a lot of stories..


Thanks for that post Maine. I've seen it wrong myself a few times.
How can I get my hands on these mythical ABYC Standards?
They sound like some good light reading.


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## mitiempo (Sep 19, 2008)

I've managed to get bits and pieces of the ABYC regs by googling but I think you are supposed to pay for the complete ones. If they want people to follow them they should be more available in my opinion.


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## boatpoker (Jul 21, 2008)

mitiempo said:


> I've managed to get bits and pieces of the ABYC regs by googling but I think you are supposed to pay for the complete ones. If they want people to follow them they should be more available in my opinion.


It costs a lot of money to produce those standards. Who do you think should pay for them ?


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## mitiempo (Sep 19, 2008)

I'm not sure what would be best. But when I look at the Canadian standards and it says to see ABYC and I can't see them it does make things tougher. It's not worth whatever they charge for an owner of a boat to purchase the regs, which are in many parts and very expensive. So they ask on a forum and get differing answers. If they were more accessible possibly more boats would comply. Or if they were government standards abiding by them would take precedence over dollars.


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## Maine Sail (Jan 6, 2003)

davidpm said:


> How can I get my hands on these mythical ABYC Standards?
> They sound like some good light reading.


You join and pay $$$..


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## hellosailor (Apr 11, 2006)

Brian-
They are probably available in a reference library, or an interlibrary loan request. You might start by asking your local library reference desk.


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## Architeuthis (Mar 3, 2008)

mitiempo said:


> I've managed to get bits and pieces of the ABYC regs by googling but I think you are supposed to pay for the complete ones. If they want people to follow them they should be more available in my opinion.


I fully agree with that, the standards, all standards should be free, as should inspections. I worked with a company that wrote the electrical code and people were required to follow them by getting a permit and inspection. Some with in the company felt that the standards were not be followed so in a "dehorn the chickens, the cows are not giving milk' move they increased the cost of the permits, required detailed drawings for all permits, charged for initial inspection and final inspection. Even I did not get a permit the next time it was required.

I realise I was talking about fresh water systems which could flood the boat but only by the amount in the tank. Interesting how many systems did not have anti-syphons. I'm not sold on the need for a valve that should always remain closed, is open only in use and use can only be done by pushing a button by the valve. Sure one can 'forget' but one can also forget to turn on the bilge pump, open the seawater valve for the engine and a dozen other more likely things.

That said if I was selling this boat I would be sure everything was to current standard or make the buyer sign off on such deficiencies.


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## boatpoker (Jul 21, 2008)

C'mon guys, nothing is free, someone has to pay for everything. I personally have always thought that Ferraris' should be free


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## Maine Sail (Jan 6, 2003)

boatpoker said:


> C'mon guys, nothing is free, someone has to pay for everything. I personally have always thought that Ferraris' should be free


ABYC is a 501c organization, non-profit. It takes money to do the education, research the standards, enforce the standards (at compliant builders etc.), run the organization etc. etc. and they make their money through membership.

ABYC is NOT a requirement for your boat and NOT a requirement for builders but it is the best set of standards we have for pleasure boats IMHO and most reputable builders follow these standards and are members.

Many West Marine stores have ABYC standards you can look at and the West Adviser is generally written to ABYC standards as is Charlie Wings book and Much of Calder's stuff.

Should those books be free too? I have no problem with the ABYC charging for membership..


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## Maine Sail (Jan 6, 2003)

sailingdog said:


> Actually, I'd point out that the LAVAC requires a siphon break on the intake line as part of its installation IIRC.


Yes the Lavac has to put the siphon break on the intake and I eluded to this in a previous post. The ONLY reason they get away with this is the massive suction/vacuum created by the huge bilge type diaphragm pump.

As I mentioned smaller heads can not often overcome the air let in by the vented loop like the Lavac can. I know that Model K's, Skipper's and PH II's can't. Siphon breaks are not intended for suction lines but with enough suction the air in, to suction volume, can be over come as is the case with the Lavac..


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## sailingdog (Mar 19, 2006)

Yes, I know you did. I was just clarifying it for those who don't know the Lavac system's installation requirements.



Maine Sail said:


> Yes the Lavac has to put the siphon break on the intake and I eluded to this in a previous post. The ONLY reason they get away with this is the massive suction/vacuum created by the huge bilge type diaphragm pump.
> 
> As I mentioned smaller heads can not often overcome the air let in by the vented loop like the Lavac can. I know that Model K's, Skipper's and PH II's can't. Siphon breaks are not intended for suction lines but with enough suction the air in, to suction volume, can be over come as is the case with the Lavac..


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