I’ve got a BCC with the head in the forward compartment. The waste tank is plastic, mounted low in the bow between the anchor locker and the head. The tank is vented but the small diameter hose ascends to the deck where it attaches to a single fitting with two screw-down covers, one for the pump-out and the other for the vent. Both need to be in the closed position. So, there is no venting. A second vent hose is attached to the top of the “vented loop” between the head and the tank. The loop is raised, mounted just under the deck. The small-diameter vent hose descends to the dry bilge under the tank. Effectively, the tank is vented only through the vented loop and inside the boat. I’m thinking that I can re-route the vented loop hose by drilling a hole into the hull near the bow, just below the deck and attaching the hose. Effectively, this would function as the tank vent. Will this be sufficient? What type of thru-hull do you use for either the waste tank vent or the loop vent?
Hmm … I’m no expert on this.
The usual expert is Peg Hall, with her book The New Get Rid of Boat Odors: A Boat Owner’s Guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor: Hall, Peggie: 9781892399786: Amazon.com: Books.
Peg Hall also answers queries on the commercially-run advertising-supported forum cruisersforum.com (to which I understand a couple three BCC owners participate). I think the sub-forum to which you might direct a query to Peg Hall would likely be: Plumbing Systems and Fixtures - Cruisers & Sailing Forums
Should you join cruisersforum.com, I can only suggest you equip your browser with an ad-blocker and so on.
I’d suggest:
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venting the holding tank has a completely different function from the vented loop.
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what you call the first vent is somehow misplaced; I think it ought not be a deck fill fitting, through the weather deck, which has to be sealed. The vent should instead be a through-topsides fitting (one through the topsides of the hull, up as high as possible) that is always open to the air and relatively protected from rain, green water on deck etc.
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a vented loop ought not produce sewage (i.e. it ought not leak). In 20 years, I don’t think Zygote has ever had a leak from the vented loop of the sewerage system (we’ve had other failures, I assure you). And if it did, I would want to know about it and clean the leak up fast - and I cannot imagine how I could clean up a leak that was transferred by hose to the bilge. I just imagine that as a recipe to create a stinking boat that could not be easily rectified. I’m a father and have cleaned up infant bums and spills - always better to be able to act fast and clean up than to have something buried in a bilge that you cannot work on in a seaway.
I repeat, I’m no expert in these matters.
- what you call the first vent is somehow
misplaced; I think it ought not be a deck fill
fitting, through the weather deck, which has to be
sealed. The vent should instead be a
through-topsides fitting (one through the topsides
of the hull, up as high as possible) that is
always open to the air and relatively protected
from rain, green water on deck etc.
I have never deliberately photographed Z’s holding tank vent. Here’s a quick crop from a photo taken during Zygote’s recent haul-out to have hull peeled back to the epoxy barrier coat (and the old epoxy barrier coat replaced with new) Can you see the unobtrusive aft-facing vent, below the rub rail and between the G and O of Zygote?
- what you call the first vent is somehow
misplaced; I think it ought not be a deck fill
fitting, through the weather deck, which has to be
sealed. The vent should instead be a
through-topsides fitting (one through the topsides
of the hull, up as high as possible) that is
always open to the air and relatively protected
from rain, green water on deck etc.
I have never deliberately photographed Z’s holding tank vent. Here’s a quick crop from a photo taken during Zygote’s recent haul-out to have hull peeled back to the epoxy barrier coat (and the old epoxy barrier coat replaced with new) Can you see the unobtrusive aft-facing vent, below the rub rail and between the G and O of Zygote?
Can you see
the unobtrusive aft-facing vent, below the rub
rail and between the G and O of Zygote?
I would suppose that that vent is similar to a fuel tank vent, some of which have a splash guard. For examples:
https://www.westmarine.com/buy/perko--gas-tank-vent-with-swivel-elbow--224738?recordNum=14
https://www.fisheriessupply.com/perko-tank-vent-with-splash-guard-0506dp4chr
And the lower priced polymer version without a splash guard:
https://www.fisheriessupply.com/sea-dog-line-nylon-tank-vents
head. The tank is vented but the small diameter
hose ascends to the deck where it attaches to a
single fitting with two screw-down covers, one
for the pump-out and the other for the vent. Both
need to be in the closed position. So, there is no
venting. A second vent hose is attached to the top
Here’s the root of the problem, I think.
Zygote carries a Ronco B125 holding tank, installed by Sam L Morse Co.
The Ronco B125 is a nominal 16 gallon tank that comes standard with:
- 1 inlet,
- 1 outlet, and
- 1 vent.
See: https://ronco-plastics.com/product/water-waste-holding-tank/
(scroll down the size range until you see the 16 gallon tanks. If you click the button beside B125 you’ll see a description of the tank and if you click the ‘Show image’ link you will see a diagram showing dimensions of the tank).
Or browse: 16 Gallon Marine Holding Tank | Ronco B125
My point is that a holding tank ought have at least one outlet (for pumping out, whether to ocean and/or to a dock-side pump out facility) and one separate vent (so air can enter and leave the tank).
Similar to a fuel tank, a holding tank has to have a vent open all the time, so air can leave as the contents increase, so oxygen is present to deny anaerobic fermentation, so odoriferous gases can exit outside the boat, and so air can enter when the contents of the holding tank are being removed.
The current catalog downloadable as a pdf from the Ronco website only lists the tanks and their dimensions.
Earlier catalogs, such as the one from 2006, had additional pages showing fittings and even a schematic guide to installation. I assume you will be able to search for the Ronco 2006 catalog if it is appropriate for you (of course the web has several other schematics showing recommended installations of holding tanks).
I’ve attached what I hope is a legible screen clip of that schematic guide to installation.
I note, to my surprise, that the schematic includes a hose from the siphon breaker/vented loop that exits the boat via a topsides thru-hull. I do think that is better than a hose that exits to your bilge, but I question - based on my experience not any particular expertise I have with sewerage systems - the need for it.
Thanks much for your thorough replies and attachments! I appreciate the time that you must have put into this, along with your previous responses to my other posts. I’ll install the tank vent as you suggest. If I’m understanding you, you do not vent the the siphon breaker/vented loop. Since my toilet flushes with no functional tank vent, on my boat (Penna) the loop vent must function as the sole vent to the tank which explains the smell inside the boat. If a correct installation of the tank vent doesn’t solve the problem, I’ll add a through-hull to the loop vent and check the hoses for odor. I do use cruisersforum.com and just took a look at some of the discussion. Helpful as well.
It seems to me that as you pump from the head to the tank, a tank vent is necessary to remove the air that is displaced. The vent on the exhaust loop can’t serve that function because the air in the tank can’t pass through the liquid in the tank. I suspect you have a leak that allows air (and stink) to escape the tank. That could be at any of the hose clamps on any of the fittings that connect to that air space. Is everything double clamped?
I agree with Bil that the vent on the exhaust loop hose should be closed. I omitted the vent on Shaula’s installation because the loop was high, passing close to the foredeck, and any siphon would fill the holding tank at worst. If you want the loop vented, I like the idea of venting it outside as you mentioned doing.
Unfortunately, I think that the commonly used sanitation hose becomes more permeable to the stink odors over time. If your plumbing is significantly more than 3 or 4 years old, it may be necessary to replace it if you want maximize stink reduction. It’s a job I’m dreading!
I should have mentioned that the tank vent hose should be connected to a thru-hull fitting, as you and Bil have suggested.
Thank you all for the information. At present there is a fitting that in catalogs usually is described as a vent, on the port side just forward of the teak trim on the bow. up high on the hull. However, it has been used as a thru-hull through which water collecting from a shower in the head compartment is pumped out. I plan to re-purpose this as the vent for the head and install new a small round bronze thru-hull to starboard to dump the shower water. I’ve seen these placed on other boats up high on the hull and also just above the water line. High makes sense to be sure it doesn’t back fill, but it also is likely to leave a streak on the hull. If any of you have a shower in the same location, where on your hull have you placed the thru-hull? Thanks, again for your help.
If any of you have a shower in the same location, where on your hull have you placed the thru-hull?
BCC 116 Zygote has Sam L Morse Co boatyard installed shower and ancillary equipment.
I’ll detail the installation, because I know that most every BCC has differences.
The shower faucets and nozzle are in the foc’s’le, directly under the scuttle hatch. That compartment also houses the head box (with the marine toilet) on the centreline, workbench and lockers to port, and hanging lockers and shelves to starboard.
The sole of the foc’s’le has a teak drain grid. That grid allows water to drain to the forepeak bilge (i.e. a bilge that is divided from the aft deep bilge by bulkhead #3). The forepeak bilge collects water from forward, including any water that falls from the anchor chain.
I also use the forepeak bilge to store anchor chain. About half of Z’s anchor chain has been hauled aft into the forepeak bilge so the chain more or less fills the forepeak bilge forward of bulkhead #3.
A strum box sits in the forepeak bilge, to keep hair and large debris (e.g. from the anchor chain).
Hose from the strum box feeds to a Flojet Quad II diaphragm 4105-143 pump, just forward of bulkhead #3. The Flojet diaphragm pump pushes water aft through nylon-reinforced PVC hose, over the hump of the lower part of bulkhead #3 and all the way to the transom.
So the forepeak bilgewater exits from a thru-transom fitting, quite high up.
With that arrangement, the Flojet diaphragm pump cannot remove all the water. Shower waste water contains skin scurf (dander) plus soap/detergent, both liable to be food for bacteria and fungi. Mud and other debris from the anchor rode also has potential to feed bacteria, of course.
To prevent bad odours from bacterial growth, we have a small handpumped siphon pump, to extract any remnant water from the forepeak bilge.
In truth, on Z we’ve hardly used the shower. Only in cold and nasty weather.
On passage and in warm temperate or tropical climes, we’ve used a garden spray on the leeward side deck. Or sponge bath using a small pail and washcloth.
Hose from the strum box feeds to a Flojet Quad II diaphragm 4105-143 pump, just forward of bulkhead #3.
My memory may be at error. The diaphragm pump is likely just aft of bulkhead #3 and in the area just forward of the mast, accessed from the sole plates around the mast. I’d need to go aboard to check. Sorry for my muddle-headedness.
I hope you found a workaround for the vent.
I’ve owned a few boats and followed Peggie’s system. One of the refits I did: removed the tiny, partially collapsed vent hose and change to ⅝. This fit to a thru-hull high on the port bow straight across from the position of the holding tank vent outlet with a gentle curve from vertical over to horizontal. For the hull outlet I bought a 5/8 thru-hull that was completely open, no clam shell vent cover. This notably improved airflow and reduced stink. Seawater rarely find its way in, but that just gets pumped out anyway.
I considered a vent on the starboard side to allow cross breeze but couldn’t get the run straight enough. Instead I made a small air horn top which screwed into the pump out fitting on deck. At anchor the boat heading into wind also aimed the horn, moving more air through the holding tank.
Any carbon filters should be removed. They foster dead air and anaerobic bacteria.
The current owners still enjoy its benefits after many years.
PS to have a pleasant interior you need dry bilges.
Fair seas
Thanks, Symphony, for your comments. The workaround that I described in Nov 2020 did the trick. I placed a new thru-hull with a seacock just above the waterline for the shower pump out.
Paul
Hi Paul,
A word of caution about bilge pump thru hulls just above the waterline: they are at elevated risk of siphoning water into the boat when heeled. I’ve experienced this boo boo. Didn’t quite float the floor boards, but it came close. On Calypso, I just installed a shower sump pump - and ran the discharge all the way back to a high point on the transom alongside the other bilge pump discharges and diesel tank vent.
Cheers,
Jeremy
Thanks, Jeremy, The shower pump/through-hull has a sea cock that is always closed, except for actual showering. I’m hoping that this will keep us safe,