Holding Tank Cross Ventilation

[pupsis]

Dear Peggie,
I have 2002 SeaRay Sundancer 310. Installing new holding tank 40Gal. Holding tank is located in the engine compartment port side. On top of the holding tank are 2 vents - 1” ID (installed on the opposite sides of the holding tank). One vent thru-hull will be on the port side and line about 4 feet. The second vent thru-hull I understand must be on the starboard side and line will be about 18 feet long. Can I achieve the cross ventilation effect in my holding tank with the second line that long? Or maybe I can install second vent thru-hull on the port side? Please advice.

 

[CalebD]

I'm not Peggy, but I've read her book "Get Rid of Boat Odors".
Two vent lines are certainly better than 1 as more air can get into the tank helping the aerobic bacteria do their work.
Her book does say: the "vent line should be as short, as straight, and as horizontal as possible, with no sags, no arches, and no bends."
This advice would seem to preclude making an 18' vent line run to the opposite side of the boat.
I see no reason why you cant have 2 vent thru hulls on the same side, located a few feet apart. That is how the tank on my boat is set up. Obviously, if the vents are located farther aft then so much the better. Vents located near the beam will be underwater at some point.

Another argument for not having such a long run for the vent is if the tank ever becomes over filled. You will never let that happen, right? When (not if) that happens the contents of your tank will want to flow out the vents, whichever, port or starboard, is lower, when the boat is heeling. Now I have a long 18' nasty vent line to clean up. No thanks.

 

[pupsis]

Dear CalebD, thank you very much for advice.

 

[Steve Dion]

Pupsis:

What are you issues with this tank? Are you having odor issues? Are you using chemicals in the tank? What chemicals are you using? Have you checked your hoses for odor?

We have a short vent hose probably 5/8" and we do not have any odor issues.

 

[Ron20324]

Any chance of making one of the vents larger, say 1 1/2 inch, then not use the second?

 

[thinwater]

You may be over complicating. The 1" vent and some Oderlos should be enough. A 1 1/2" vent would do it without chemical.

 

[AnsleyS]

Pupsis,

I installed my tank with Peggie's help and I put two one inch vent lines out the port side. I pierced the hull just below the deck and put one thru hull above and one below. Then I put on two clam shell vents, one facing forward and one facing aft. When at anchor or the mooring the wind is from the bow and the forward facing vent helps move air thru the tank. I figured that it is possible to get water into the vent line but I would have to bury the rail forward of the beam and on a thirty nine footer this does not happen often.

Then use a biological tank cleaner and don't kill the bugs in there with any formaldehyde treatments. Raritan's KO is good and use their CP for cleaning.

 

[shannon28]

pupsis - i'd say go with the two 1" vents on the same (shorter hose length side) as has been suggested. Your SeaRay won't be doing much heeling so there's little worry there and with the vent lines coming of the aft end of the tank it should work just fine.

The biggest issue with any side mounted vent is clogging. Just make sure the lines move steadily upward with no sags or dips. And make sure thee vents are cleared from time to time.