Holding tank in the bilge?

[Don C L]

OK everyone I got a question, is there a kind of bladder that is designed for this purpose?
oops, never mind, found them... so why not use a bladder in the bilge?

[David B]

Originally Posted by Don C L

OK everyone I got a question, is there a kind of bladder that is designed for this purpose?
oops, never mind, found them... so why not use a bladder in the bilge?

Full of freshwater - OK
Full of Diesel - Hmm
Full of sewerage - No way.

Yes, they are available, and if I was to use one, I would be sitting it on top of a synthetic felt pad, which ran up the sides etc to protect from chafe. But down there flopping around as you go through a seaway - over the years, those seams are going to be stressed a lot, and like water beds (we have one) there is is a chance they eventually let go. Even if the bilge area is perfectly sized, the fluid contained within is still going to surge from one side to the other, from one end to the other. They are very tough, but .....

[GarthGregory]

My Beneteau 473 - The 3 x heads holding tanks are Roto Moulded and are 50 Liters each . The tanks are in each of the heads compartments above the water line and discharge through a ( approx ) 80 mm I D pipe . I have tried many systems over the years and this seems the best and the simplest . In ten years I have removed and air dried the tanks once and used a rubber mallet to loosen the build up . At the end of every season , I have put 10 x liters of vinegar in each tank for minimum of 24 hours and then drained and flushed the tanks with sea water and left them to air dry in situ . I checked them after 6 x years and there was almost no build up at all . We also put paper through the system and we ( and our Guests ) have never had a blockage of any sort .
A smelly tank on a yacht is awful , our system ( Beneteau ) is way ahead of all the types we have tried on various charter yachts . The large diameter discharge pipe is definitely the key to the success of the system . Hope this helps .

[Peregrine1983]

Thank you all for the replies.

David B - I think we are going to go with a larger single holding tank (because we do often spend extended time in harbors) and a single overboard discharge diaphragm pump, but thank you for the info about your system. I was recently on a charter boat with that setup and it was fantastic, but we never spent more than a day or two in a harbor, so the small holding tanks were OK.

Don C L - A bladder does seem like the logical choice for an odd-shaped space, or a space with a small opening to get the tank in, but I always hear that same response about them eventually permeating... which has scared me off. I am starting to think that anything flexible (hose or otherwise) will eventually permeate and stink.

Peggie - I'm sitting here with your excellent book in front of me as I type this. For the general good I figured I would ask these questions in the open here on the forum. I hope that's OK. My new system design at this point involves two heads going to one new Ronco 28.5 gallon (or similar size) holding tank under my settee. I plan to use PVC for my pipe runs and high grade hose where it's needed. My two head waste outlets will run to a tee, then into a 1 1/2" inlet on the top of holding tank. There will be a 1" vent hose coming out of the top of the holding tank going up to the deck. There will be one single 1 1/2" outlet at the bottom of the tank. This outlet hose (according to Page 26 in your book) should go into a Y-valve. I plan to have this Y valve switchable between my diaphragm pump (which will pump to my discharge through hull) and my deck pumpout. The discharge through hull for the diaphragm pump I also plan to share with my forward head's direct discharge. So, there will be another Y valve upstream of my diaphragm pump to switch to the forward head from the holding tank.

Hope this is clear. Does this sound kosher to you?

Also, do I need a check valve between my discharge through hull and my diaphragm pump? In your book, you mention that check valves are necessary to keep things moving in the right direction, but I am not sure if the diaphragm pump acts as its own check valve or not.

Thank you very much for your help.

[Peregrine1983]

Originally Posted by GarthGregory

My Beneteau 473 - The 3 x heads holding tanks are Roto Moulded and are 50 Liters each . The tanks are in each of the heads compartments above the water line and discharge through a ( approx ) 80 mm I D pipe . I have tried many systems over the years and this seems the best and the simplest . In ten years I have removed and air dried the tanks once and used a rubber mallet to loosen the build up . At the end of every season , I have put 10 x liters of vinegar in each tank for minimum of 24 hours and then drained and flushed the tanks with sea water and left them to air dry in situ . I checked them after 6 x years and there was almost no build up at all . We also put paper through the system and we ( and our Guests ) have never had a blockage of any sort .
A smelly tank on a yacht is awful , our system ( Beneteau ) is way ahead of all the types we have tried on various charter yachts . The large diameter discharge pipe is definitely the key to the success of the system . Hope this helps .

When I mentioned in my above post that I was on a boat with this system it was a Bene 473. I loved it. 50 liters each (13 gal) is great. I didn't realize they were that large. Hmmm... Decisions decisions.

[Robert E]

Dear Peregrine 1983,


As part of a major refit of our Nonsuch 33 we removed the waste bladder from beneath the forward berth, all hoses, the manual pump and rebuilt 2 thru hulls. The odor was awful. We replaced a 40 gallon aluminum water tank in the central bilge with a custom plastic one, the best hoses, macerator and a simple waste to the tank, pump out, or overboard where allowed.


Yes, the bilge is a perfect location for the waste tank. Make the system as simple as possible. Use the highest quality components, particularly holes. Venting across the tank encourages the growth of proper bacteria. Good luck.

[SuW]

Just on the subject of unpleasant boat smell, we solved our problem with a 1976 fiberglass boat by painting the entire interior with enamel paint. The inner liner (gelcoat) was producing a smell not dissimilar to "that head smell".
I don't think the boat had absorbed the smell, I think it was being created by the interior liner.
We did get the boat cheaply, though!

[SouthernPride]

I used to design and install big KOI ponds. Something to consider... Run two lines of schedule 80, space permitting, and a couple of gate valves. Having the ability to bypass a problem line or broken line helps save time and aggravation immensely. As some have said sweeps also help. On the sweeps get a couple that have access valve offshoot with a nut screw access option for blockage, washouts , etc...
Tilt the tank a few degrees lower towards one corner. Helps washout and emptying... Although most new tanks these days have a low spot.

[David B]

Originally Posted by Peregrine1983

When I mentioned in my above post that I was on a boat with this system it was a Bene 473. I loved it. 50 liters each (13 gal) is great. I didn't realize they were that large. Hmmm... Decisions decisions.

It is a simple and very effective system. Our tanks are 80 litres each (two heads), so that is greater capacity (41 gals) than the single tank you are thinking of installing.

Whatever you do, keep it as simple as possible.

[Bridger]

Hi, I'm considering a holding tank low in the bidge as well. From another thread I learned of the Whale Gulper pumps which can pump up 9 feet so that's plenty for overboard discharge. Just want to confirm the average marina vacum pump out can pull the contents out how far? I could be 8 feet from the deckfitting? Will that be a problem?

Thanks, Marty

[Kim Gregory]

The bottom of my holding tank is 5 feet below the water, and have had no problems getting it pumped out.

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