Black water holding tank in a Swan 41:

Hello every-one.

Having a holding tank is becoming compulsory in more and more anchoring places these days, and I believe it is justified.

I have been scratching my head for a while trying to decide where I could put such a tank, and not found a really convenient place. If I put it under a bunk either in the rear cabin or the main one, I am afraid of smells. Also under the cockpit the access is rather limited, and it is probably a bit far away from the heads.

There are also electrolysis systems (electroscan?) 

Could we share your own experiences?

Many thanks, and happy sailing to all.

Philippe. 41/022

Dear Phillipe,

  Among the drawings that came with my Swan 41 there is one for the plumbing installation. On this are references to the optional toilet holding tank, however the general accomodation drawing does not show where it was fitted! Perhaps Lars can enlighten us.

regards, Cosmo Little

Dear all

A holding tank was a very unusual feature at the time of build. The location was decided considering other equipment, which is likely to be the situation also today.

Take care to use odour tight hoses suitable for this application.

Kind regards

Lars

Here a suggestion for the plumbing.

Sorry for being hypercritical but I would suggest that the circuit branch from the WC to the tank enters the tank from above.

Daniel, 411-004

Daniel

Forgive me for this rough sketch, you are perfectly right. Pls note, however, that sometimes it is not possible to go through the top, but the system works anyway.

Best regards

Lars

Dear Philippe

Referring to your concern about smells - using rigid PVC pipe for the plumbing would be a better alternative although this is seldom used on small craft.

Best regards

Lars

I have installed a black water holding tank on my Swan 411, which I suspect is very similar to that which might be required on a Swan 41. Lee Sanitation www.leesan.com are very helpful in providing advice on how to design a suitable system. They could provide a custom plastic tank. I purchased a stainless steel tank from Nautor at not inconsiderable cost, which I subsequently needed to modify on the advice of Lee Sanitation. This has worked very well.  I can look out my piping diagram. I suggest that you install a spectacle valve immediately behind the toilet pump as it makes the routeing of the effluent to sea/tank very easy. I have a Plastimo toilet and this spectacle valve fits it. A large diameter vent pipe is essential if the vacuum pump out is not to collapse the holding tank! My tank has a separate vacuum pumpout outlet over and above the mechanical pumpout outlet. It is essential to use odourless sewage grade plastic piping. This can be supplied by many chandlers or by Lee Sanitation. My other advice is do not use a macerator pump as the almost always seize up. It is better to use an electrically driven diaphragm type pump. Whale Pumps manufacture such a pump.

Please contact me if you require further information

Anton Fawcett

Hello everyone, thank you for all this precious information.

Anton I am not sure what is a spectacle valve: I have seen on chandlers catalogs that there are specific three way valves which I suppose do work well. I also have been on lee sanitation's site, and have an article of PBO which describes the piping, pumping etc...  So for the theory I feel almost OK!

BUT in any case your own experience is invaluable.

The last info I am looking after now is where to put that tank, and which capacity. Today I see two possibilities: either under the starboard upper bunk of the saloon (ie just next to the chart table) or under the starboard bunk in the rear cabin. One also needs space and access for the pump which might not be easy for the rear cabin option.

So Anton, where did you install it in your 411? And are you happy with it?

I read that stainless steel was not a recommended option for a holding tank (corrosion)? May-be that's one question for Lars?

Many thanks again. Kind regards, and happy sailing!

Philippe Vidal 41/022

Philippe

In order to comment on the tank material question I need to know where to find the information you refer to.

Lars

Dear Professor,

I read this information (on stainless steel holding tanks) in two different articles. One from Practical Boat Owner (april 2005),

one found on the internet from the Connecticut Department of Environmental Protection: http://www.ct.gov/dep/cwp/view.asp?a=2705&q=323760&depNav_GID=1711

where there  is also a lot of info on the recommended design of the system.

I must admit that the statements against stainless steel are very general. The recommended options are polyethylene or polypropylene tanks.

.... but there is nothing like experience, that's why I brought this question!

Grateful regards.

Philippe,

Our 1974 Swan 38 was equipped with a >100 liters stainless steel holding tank by Nautor right from the beginning, as the boat was to be launched on Lake Constance, where the regulation is very strict. The holding tank is located under under the port side settee of the saloon, just forward of the chart table. The system is installed as in the sketch provided by Lars, excluded the option to pump right from the bowl out into the sea.

A few years ago I unfastened the tank and cleaned it thoroughly using sodium hypochlorite. There were no signs of corrosion. However, the boat has been sailed for the first 30 years in fresh water environment, which may have some role also here.

I think acid resistant stainless steel makes a sturdy, odor-proof and, so it seems, corrosion resistant holding tank.

Concerning the hoses, I have been told that hoses made with inside lining of butyl rubber are the most impervious to odour.

Best regards, Jyrki

Hi,
in my 411-004 the tank was originally installed by Nautors in 1977 and was placed under the starboard bunk of the forward cabin. This is a quite convenient position but it is not applicable to the 41 as the head is elsewhere.
It was made of stainless steel and operated until few years before 2001 when I bought the boat. At that time the tank was laying in a garage and only few holes here and there in the toilet remained as a sign of the previous system.
I had the tank inspected from a skillful marine blacksmith who advised to rebuild it because the weldings and nearby parts were badly corroded. I had it rebuilt identical to fit the same position.
Corrosion of the welding in SS is a well-known issue that can be avoided by skilfully welding or by coating. Another cause of corrosion in SS is oxygen starvation but I ignore how much this would be an issue in an holding tank.
Restoring the whole system in its original position was very easy and straightforward.
A vent hole is just beside the vent of the shower/sink sump on the side of the hull and the diverting Y valve is behind the Blake´s toilet. The diaphragm flushing hand pump is under the sink. Presently, there is not a deck flushing line because in this part of the world I have never met any flushing station but there is a port in the tank ready for it.
I finish the story saying that in fact I am quite proud of having the holding tank because in Italy there are very, very few boats of the age of mine with such civilized facility!

Daniel, 411/004

Philippe & al

Hi Phillipe

A spectacle valve is a valve which can divert water in two or more directions by moving a lever which is a flat piece of plastic, which blocks off one or other of the orifices. You can find one on the EC Smith website www.ecs-marine-equipment.co.uk. It is the RM68 Valve 1. This fits immediately behind a marine toilet outlet and fits a Plastimo toilet.

I put the tank in the starbord bin in the forepeak immediately below the pipecot. The capacity of the tank I do not know, but it pretty well fills the bin on the 411. The pump out pump to use is a Whale Gulper electrical toilet pump. You can find details on www.whalepumps.com. You will need to box in the holding tank to avoid smells. This is a somewhat fiddly job, but is in the end not that difficult. A shipwright would do it in a couple of hours!

I am delighted with the installation of my holding tank. There is virtually no smell and it is not difficult to use. I have put the electrical toilet pump under the wash basin in the heads. The three way valve, which directs effluent either from the heads via the spectacle valve to the sea, or from the holding tank via the pump to the sea, also sits under the wash basin in the heads. You will need to drill a number of holes in the bulkhead between the heads and the sail bin in the forepeak to take the pipe work. You will need to use a hole cutter of the appropriate diameter. In order to provide a suitable U bend to stop effluent getting into the breather/activated charcoal filter I used the space at the back of the cupboard in the heads. The run of the pipework needs a lot of thought. I have to say it took me some time before I worked out the optimum solution. Unfortunately my boat is in Gothenburg so I cannot send you pictures of the pipe work.

I suggest that you send me an email. You can find it on this site. I would be only too happy to help you. We could then talk on the phone.

Best regards Anthony

Thank you Anthony and Daniel, and professor!

This time I believe I have most of the precious information.

Only problem now is that the position of the toilet compartment in a 41 is in the center of the boat, which makes positioning of the tank a bit more complicated. I will give it some thoughts and keep those interested posted.

Kind regards.

Philippe

I too had to do this in my 41 and I located it under the starboard berth in the aft cabin.  I really don't think there is any other practical location.  I would highly recommend stainless steel, as we have not had problems with odor and I think this may have helped.

Thanks a lot CBinRI.

I came to the same conclusion after all these discussions. Could you please add a few details such as capacity of the tank, type and location of the pump to empty the tank, etc... Also: do you still use the original Baby Blake toilet? A photograph or two could also help me.

Many thanks for your help.

Kind regards.

Philippe. 41/022

I am embarassed to admit that I do not know the answers off-hand.  I can't recall the tank size and I am not aware of the head manufacturer, although I think it's original.  I also have no pictures and the boat is too tucked away for winter for me to have any for you soon.  I guess I win the "Mr. Unhelpful" award for today.  I used Jamestown Boat Yard to install it.  Best of luck.