Waste Line Vents

[Duncan Maio]

My CD27 has a small holding tank under the port side of the V Berth, with a vent hose that runs forward to the chain locker and then up to the bow, where it exits at a fuel-vent type through-hull. This vent line tends to trap liquid because of the long horizontal run, and the through-hull clogs as well.

I intend to rework the vent hose to eliminate any low spots if possible, but thought that adding another vent might help. I also want to vent the vented loop to the outside. The current plan is to add a 1/2" or 3/4" bronze through-hull at the rubrail adjacent to the head, and connect it to both the vented loop and the holding tank.

Is this a good idea? Any other thoughts?

-Duncan Maio
s/v Remedy
CD27 #37
Bristol, RI



dmaio@meganet.net

[Ed Campbell]

My CD27 has a small holding tank under the port side of the V Berth, with a vent hose that runs forward to the chain locker and then up to the bow, where it exits at a fuel-vent type through-hull. This vent line tends to trap liquid because of the long horizontal run, and the through-hull clogs as well.

I intend to rework the vent hose to eliminate any low spots if possible, but thought that adding another vent might help. I also want to vent the vented loop to the outside. The current plan is to add a 1/2" or 3/4" bronze through-hull at the rubrail adjacent to the head, and connect it to both the vented loop and the holding tank.

Is this a good idea? Any other thoughts?

-Duncan Maio
s/v Remedy
CD27 #37
Bristol, RI

Duncan:
My CD25 was thusly equipped when I got her. The vent scooped up the sea very nicely when hard on starboard tack (once filling the bilge when the vent line went adrift). Don't put any holes in the hull below the rub rail unless you intend them to take in water at least part of the time.
Regards,
Ed Campbell
CD25 "Cassiopeia"



campbell@waltereden.com

[Duncan Maio]

Don't put any holes in the hull below the rub rail unless you intend them to take in water at least part of the time.

Ed:

How did you remedy the situation? where does your holding tank vent now?

-Duncan



dmaio@meganet.net

[Tom Shelford]

My CD27 has a small holding tank under the port side of the V Berth, with a vent hose that runs forward to the chain locker and then up to the bow, where it exits at a fuel-vent type through-hull. This vent line tends to trap liquid because of the long horizontal run, and the through-hull clogs as well.

I intend to rework the vent hose to eliminate any low spots if possible, but thought that adding another vent might help. I also want to vent the vented loop to the outside. The current plan is to add a 1/2" or 3/4" bronze through-hull at the rubrail adjacent to the head, and connect it to both the vented loop and the holding tank.

Is this a good idea? Any other thoughts?

-Duncan Maio
s/v Remedy
CD27 #37
Bristol, RI

Duncan the most complete info to answer your question can be found at Boatbuilding.com. They have a whole paper on your problem It,s titled MARINE SANITATION : FACT vs FOLKLORE



TShel11523@aol.com

[John R.]

Don't put any holes in the hull below the rub rail unless you intend them to take in water at least part of the time.

Ed:

How did you remedy the situation? where does your holding tank vent now?

-Duncan

I've seen info on some high end boats $$$ (I think Alden or Hinkley) that used the lifeline stanchion as a vent "stack". They machined (drilled) a series of about six small holes in a vertical pattern at near the top of the stanchion. They had a hole going through the deck up into the stanchion. They had some sort of fitting for plumbing the hose or pipe to that hole. I think that was a clever idea to get the vent high above any water intrusion sources.

I'm building and installing a new tapered bow holding tank in our CD30 at this time and I've installed two vent ports in the tank. One will go to the existing hull vent fitting on starboard bow and the other on port. I'll be plumbing the head discharge line vented loop fitting to the head intake line vented loop fitting and then both of them together to a hull vent fitting. That eliminates any venting inside the boat and eliminates odors. The vent fittings on the vented loops need to be serviced regularly so I lubricate the hose before clamping onto the vent fitting. That makes them far easier to remove to access the valve in the loop vent fitting for cleaning. I've applied that method to a couple of boats with odor problems and it works well.

I'm replacing all the CD30 head hose with PVC and very short premium head hose couplers for flexibility. I'll be posting more info on the tank construction in the near future and will have photos of the construction available to anyone contemplating the project for themselves. The tapered tanks are difficult to build due to their compound angles. However, the tank should outlast the boat, very robust. Plastic tanks can't compare. A far better tank than the polyethelene ones commercially available and about $125+ cheaper excluding labor.

[Duncan Maio]

I'll be plumbing the head discharge line vented loop fitting to the head intake line vented loop fitting and then both of them together to a hull vent fitting.

A far better tank than the polyethelene ones commercially available and about $125+ cheaper excluding labor.

John:

Thanks for the pointers; I may just try the stachion trick. Where do you intend to locate the vent for the vented loops?

Also, what material are you using for the tank?

-Duncan



dmaio@meganet.net

[Duncan Maio]

Duncan the most complete info to answer your question can be found at Boatbuilding.com. They have a whole paper on your problem It,s titled MARINE SANITATION : FACT vs FOLKLORE

Tom:

It's a great article, and what got me started (and kept me from building custom stainless steel or aluminum tanks).

Here's my problem: The article says that vent lines should be as short and as horizontal as possible, with as few turns as possible and no vertical rise above 45 degrees. My holding tank is at/below the water line at the aft end of the V Berth, with a vent line that runs forward to the chain locker, then vertical to a vent at the rub rail. I can, I think, take the low spots out of the line and angle the rise somewhat.

I think that adding a 3/4" vent line above the tank (at the vented loop, with a tee to the loop and the holding tank) will provide the "cross ventilation" the article describes, but I don't want to put extra holes in the boat if they will not be helpful and might be harmful (e.g., filling the boat on a starboard tack).

-Duncan Maio



dmaio@meganet.net

[Mike Thompson]

I have a CD28 with the holding tank in the same place as
yours (under port v-berth). The following routing of the
vent line has given no trouble:
Vertical from the tank to underside of the deck.
Horizontal (actually a gradual incline due to the sheer)
to the anchor rode locker. Then there is an inverted
loop through 360 degrees to reduce water entry.
The vent is a few inches below the top of the incline
previously mentioned.

Mike
"Haven"

My CD27 has a small holding tank under the port side of the V Berth, with a vent hose that runs forward to the chain locker and then up to the bow, where it exits at a fuel-vent type through-hull. This vent line tends to trap liquid because of the long horizontal run, and the through-hull clogs as well.

I intend to rework the vent hose to eliminate any low spots if possible, but thought that adding another vent might help. I also want to vent the vented loop to the outside. The current plan is to add a 1/2" or 3/4" bronze through-hull at the rubrail adjacent to the head, and connect it to both the vented loop and the holding tank.

Is this a good idea? Any other thoughts?

-Duncan Maio
s/v Remedy
CD27 #37
Bristol, RI

tmike@ma.ultranet.com

[John R.]

I'll be plumbing the head discharge line vented loop fitting to the head intake line vented loop fitting and then both of them together to a hull vent fitting.

A far better tank than the polyethelene ones commercially available and about $125+ cheaper excluding labor.

John:

Thanks for the pointers; I may just try the stachion trick. Where do you intend to locate the vent for the vented loops?

Also, what material are you using for the tank?

-Duncan

Duncan,

The vent fitting is located just under the rubrail as high as possible.

The tank I'm building is constructed of 15/32" (1/2") BC exterior grade plywood. All tank panel sections (tapered sides, bottom, top, front and rear) are assembled with thickened West System epoxy used on all seams and screwed together with #6 flathead stainless screws in 1" and 1-1/4" lengths. The front of the tank is double walled ( 1" thick ) where the bronze discharge fitting and vent fittings are installed. The rear wall is doubled only where the inlet fitting is installed.

All interior seams will be filleted with a thickened West mixture. All interior surfaces will be glassed with West and 12 oz. cloth. Over that a 2" glass cloth tape will be applied to all the seam joints for extra strength. A total of about 22 mils of epoxy with West barrier coat additive will be applied as a final interior finish. The exterior will be glassed over as well and final finished with polyurethane topcoat such as Interthane. All tank fittings are bronze. The inlet fitting is a 1-1/2" Perko thru hull. Onto the thru hull will be attached a Shields 1-1/2" glass reinforced sanitation hose barb (similar to Marelon). The outlet and vent fittings are bronze threaded couplers epoxied into holes in the tank wall. The outlet is 1 1/2" and the vents are 1/2". The pick up tube on the inside of the tank is schedule 40 PVC and is supported by two 3/8" thick baffle boards that bridge the width of the tank at two different depths. The top of the tank is fitted with a custom inspection access port that also serves as a "tank full" indicator unit (no moving parts at all) that will switch on a indicator light in the head compartment when the tank is full to about 3" under the top.

[David Brownlee]

We fixed this problem on our CD 27 serveral years ago by re-routing the vent line between the tank and the forepeak. I explain this in detail in an earlier posting. It really works.

Ann and David Brownlee
WINDRUSH
CD 27 #181
Havre de Grace



dbrownle@sas.upenn.edu