The Plastic Classic Forum, your free and in-depth resource for information on re/building classic sailboats. ... Be sure to visit / join our sister site at sailFar.net! ... And don't forget to check out Atom's Virtual Home Port! ...
The holding tank vent fitting looks like the Perko fitting I am about to install on my boat. I thought it was stainless steel but you stated it was zinc plated on your website. It looks nasty. I don't suppose you recommend it, would you? What are you planning to use instead?
Also, as for the location of the vent can you please discuss the pros and cons of topside vs. deck (next to the toerail)?
The fitting is chrome-plated zinc. I installed it in April 2002.
It's Perko #506. Obviously, I don't recommend this one.
In it's place I'm either going to install this Perko #509, made of chrome-plated bronze...
...or this one, touted as "polished bronze" from Hamilton Marine:
I'd discuss more about how the vent works in its location, but I think I have to plead the 5th against self-incrimination. Suffice it to say the new vent is going in the same place.
---------------------------------------------------
Forum Founder--No Longer Participating
No worries Tim. Your comments are protected by attorney client privilege :-) My only concern of the topside location is that most of the time Triton rails are under water. I don't know if water will be syphoned into the holding tank.
David, the stanchion idea is ingenious. I have to think about that. Have you done the same? BTW, I have been reading over and over again how you conquered the Bristol29 weatherhelm problem with a bowsprit and a shortened boom. Those are on my to further explore list. I am so tired of the weatherhelm.
Triton106 wrote:My only concern of the topside location is that most of the time Triton rails are under water. I don't know if water will be syphoned into the holding tank.
I've not had an issue with this. This might be more of an issue if the vent were more amidships, rather than nearly at the bow (which isn't underwater when heeled). Waves are one thing; full submersion when the rail's down might be an other.
---------------------------------------------------
Forum Founder--No Longer Participating
I deep-sixed a chrome plated zinc holding tank vent fitting for having corroded full (meant that we could not pump anything into the tank!) and replaced it with the Perko chrome plated bronze fitting from West Marine. After 4 seasons, the chrome is about gone and the bronze is very deeply pitted. (Leaping just a little, this is one of the reasons for my grumps and nags about the way our suppliers buy from unverifiable sources.)
I replaced the pumpout fitting which also was zinc with a solid stainless one; it's nice but I wish that someone made a stainless vent fitting!
As for dipping a vent in the water when the boat heels, I suggest moving your vent to the transom. You'll very seldom dip it there but even more importantly, the folks in the cockpit will much less often be reminded that there's a holding tank and a vent forward and to windward! Wish I'd taken my own advice when I had the head apart this past spring but sloth and the pain involved in passing a hose some 20' to the stern, not to mention filling and painting the old hole, won out.
"The key to the airflow through the tank is mounting a vent on each side of the bow. In the same manner that air flowing along the sail creates a high-pressure zone on one side and a low-pressure zone on the other, so it is with the airflow down the hull. As long as the airflow is not exactly symmetrical, the same effect will be seen. Since the pressure will be greater on one side relative to the other virtually all of the time, air will flow through from that side to the other. " - George Dinwiddie
I believe George is quoting Peggy Hall about the in and out venting idea. I don't agree with much Ms Hall has to say about marine sanitation, and I doubt that two 3/4" diameter hoses going to thru-hull vent fittings would actually create any air movement as Peggy thinks is so important. I believe for her idea to work you would need 3" vent hose, vent cowls to pick up air and channel it, etc. Not sure I want open pipes to my holding tank any more than I would want to vent the underground septic tank in my front yard.
Last edited by David on Tue Oct 21, 2008 3:04 pm, edited 1 time in total.
I believe Peggy is correct about what happens when your holding tank gets depleted of oxygen. (as an aside, Peggy stayed with us one year while attending the Newport Boat Show. She is a nice lady and a real character.) I had a horribly stinky tank on my Pearson 30 from the PO, that I since replumbed. The vent went to the transom but was a cheezy piece of garden hose with an obvious dip in it that would trap water and thus shut off the vent. I ran a piece of solid 1" pvc pipe along the deck hull joint (on the inside) from the area of the holding tank aft to the transom area. I connected a piece of 3/4" ID hose at either end of the pipe to the holding tank on one end and the transom vent fitting on the other. The solid pipe allows plenty of breathing and can't trap water under any circumstance. I have had zero odor problems since.
Venting forward near the bow or the transom makes sense to me. The only thing I would like to understand is that, depending on the location of the holding tank, venting in those two location will invariablly involve much longer runs of vent hose. I understand that vent hose should be as short, staight and wide (within reason) as possible. The location and the length of the run will conflict in my case since my holding tank is outboard of the toilet which is between the V-berth and the saloon.
