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Holding Tank Vent design

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adamb
1st Mate

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USA
39 Posts

Initially Posted - 02/09/2005 : 21:10:12

Visited the Head Mistress – researching the dreaded odor issues associated with marine sanitation.

Learned something a bit disconcerting – wanted to share and get some feed back.

On the subject of venting the holding tank

“We prefer to put holding tanks in the bow of sailboats – under the V berth – because the hull just behind the point of the bow is the only place on the hull except the transom that will never be under water when the boat is on heel; it’s the perfect place to install vent-line through hulls”

Her reasoning is that holding tank vents need to be horizontal to 45 degrees off horizontal in order for them to work – otherwise the now ambient air exchange takes place…

Now, as for me, the last thing I want to do is put another thru hull in my boat (even above the water line..). My current vent is vertical from the holding tank (in the port berth in the main cabin) through the deck, next to the pump out piping.

I am engaged in this whole palaver due to odors, and the fact that my piping is a least 8 years old (as is the tank) and so was thinking of just a replacement program.

Any feed back on Holding tank venting, etc.?

Norwegian Blue
Jacksonville, FL
1984 Standard Rig, Fixed Keel, Traditional Layout

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 02/09/2005 : 22:55:53

adamb<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Any feed back on Holding tank venting, etc.?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">First, let me say that you should pay close attention to what Head Mistress Peggy tells you! She knows her ...um...waste.

When I switched from a porta-potty to a marine head, I installed a sort of inverted pyramid shaped semi-custom holding tank under the pointy end of the V-berth. I had the tank built with two 1" vents on the centerline of the top surface. I used 1" waste hose to two nylon thru-hulls located in the forepeak just below the anchor locker pan (under the whale-eye nav. lights). I used 1-1/2" "SeaLand OdorSafe"(sp?) waste hose from the head to the tank, and from the tank to the discharge. That installation has been in use for several years with no odor issues at all.

Three key points are:

1.) Thick (3/8"), rigid, polypropelene(sp?) tank.

2.) Ratitan K.O. biologically active holding tank additive.

3.) Two large diameter vent hoses.

With the vents on opposite sides of the bow, there is always at least some air pressure differential across them, resulting in a crossflow of fresh air in the tank. This supplies oxygen to the "good" bacteria and constantly removes any odor from the "bad" bacteria. All of my suggestions are noticably more expensive than the more typical installation. I'm a firm believer in doing head plumbing right the first time.

If the lady aboard says, "Ew! Something stinks in here!"

Responding, "But Honey, think of the money I saved!" isn't likely to appease her.

-- Leon Sisson

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SJ
Navigator

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USA
198 Posts

Response Posted - 02/10/2005 : 19:42:20

Leon,
Do you have any photos that would help show the design???

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 02/10/2005 : 21:12:50

SJ,

I might be able to take some photos or draw some sketches for you. Can you be more specific about what you'd like to see?

-- Leon Sisson

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SJ
Navigator

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USA
198 Posts

Response Posted - 02/11/2005 : 14:17:52

I'd like to see how you installed the venting and thru hulls...Thanks, as I am undertaking this conversion this spring....

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 02/11/2005 : 20:21:58

SJ,

Here are some photos of my holding tank installation.

The first image was shot in the V-berth looking forward. With the forepeak panel removed, you see the two vent lines coming up through the very front of the hull liner and going to nylon thru-hulls. The thru-hulls are glowing like fluorescent lights because it's sunny outside.

The second image shows one of the nylon thru-hulls just below the whale-eye nav. light.

The third image was shot in the V-berth looking down and forward with the locker hatch open. In it you can see the holding tank, its mount, the 1-1/2" upper inlet and lower outlet hoses.

The fourth image was shot looking down and slightly aft into the V-berth locker. In it you can see the 1-1/2" waste hoses and the offshore discharge pump and seacock. The 1-1/2" T-fitting is where most similar systems would have a Y-valve. The leg of the T goes to the pumpout deck plate. The 3/4" white hose is the head inlet from a T-fitting in the sink drain hose. The white canister-looking thing is the shoot-through-the-hull depth transducer housing.

Sorry the locker looks so dirty. I hadn't looked in there for nearly a year. Appearently some rain water got down there when I left the forward hatch open, and allowed mildew to get started on everything. The rest is rust stains from that old spare Danforth anchor and its chain.

-- Leon Sisson

Edited by - on

SJ
Navigator

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USA
198 Posts

Response Posted - 02/12/2005 : 08:50:42

Great pics! Now I know what to do...Thanks again!

SJ

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 02/12/2005 : 21:06:56

The cat litter experiment has been going on for a while now. So far the results are good. A vent is required and some reajustment but its simple, clean, no odor, no thru hulls, no pumpout, just a container( 5 gallon bucket) some trash bags, and a bag of cat litter. Updates to follow. Dave

Edited by - on

ChrisDara
1st Mate

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USA
88 Posts

Response Posted - 02/19/2005 : 09:51:51

Hey Leon

Nice job. You mentioned the tank was somewhat custom. Who made it or did you buy one and make some changes yourself?

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 02/19/2005 : 11:50:20

ChrisDara,

I think I ordered the holding tank from Raritan (which I misspelled above). It's a 16gal. model, or mold number, 16B373 with custom openings.

Here's the way this works:

1.) I got access to their catalog of molds which has simple but usable sketches of the stock tank shapes they are equipped to produce.

2.) I whipped together a sturdy cardboard and duct tape mock-up of the most likely tank shapes to see which one would fit best.

3.) I made or modified a sketch of what tank openings I wanted, and where. (Hint: mark openings directly on the mock-up while it's in place in the boat.) One thing I might do differently would be to put the holding tank outlet on top with a dip tube inside like a marine fuel tank. This would put all the openings on top of the tank, and greatly reduce the (already low) risk of a holding tank fitting causing a liquid leak. (Remember to include a cleanout opening. I ordered a 4" Beckson plate in the holding tank, and a 6" one in the water tank. I then FAXed that sketch to Raritan's tank engineers.

4.) They converted my sketch into their formal fabrication drawings and an agreement to purchase. They then FAXed that back at me for approval and signature.

5.) When Raritan got back my signed copy of their drawings (and my credit card number as I recall), they built the tank and ship it.

6.) I then added plumbing fittings and fabricated tank mounts.

Got all that? I ordered two tanks from them, and the whole process went very smoothly. The tanks are translucent, so it's easy to see how full they are.

-- Leon Sisson

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