Some final 'head' thoughts: The world has changed and it was while rebuilding Nellie's sanitation system that this point was driven home in some interesting ways. The old sanitation design (see first diagram below) reflected the mores of its time. Nellie's new design (see second diagram below) reflects today's rules and maybe, even some of tomorrow's. Almost everywhere in US waters it's illegal to pump the head directly overboard. In fact, where we normally cruise, the inland waters of the east coast, even having an open head through-hull is a fineable offense. So, how does this affect Nellie's sanitation design? Surprisingly in some dramatic ways, and mostly for the better.
When, by law, a normally-open through-hull becomes normally-closed, it's a game changer. There's a cascading affect on the sanitation system's design. The design used to require an anti-siphon and a three-way valve. The first kept the boat from flooding via the always-open thru-hull. The second allowed toilet waste to bypass the holding tank and go directly to the thru-hull. Now, redesign the system about a closed thru-hull and things get simpler. All toilet waste goes to the holding tank. From there the waste is either pumped overboard or vacuumed out via the foredeck fitting. Here's the up-side: by removing the anti-siphon and the three-way valve we eliminated 30' of hose, a dozen hose clamps, and myriad sources of potential 'stink'. A good trade I think against the ability to flush the head directly overboard. This project also resulted in some interesting lessons learned:
1. The old 3/4" vent line was mostly clogged at its connection to the holding tank. The new vent line slopes upward from the tank fitting so that sloshing effluent will drain back into the tank with enough speed to scrub the line's walls.
2. Don't use brass fitting in a sanitation system—they'll dissolve. Use PVC or nylon.
3. All effluent lines slope towards where they drain to eliminate 'standing' effluent and the resultant odors.
4. The same long-moleculed plasticizer which makes PVC hose flexible also makes it more permeable to odors than solid PVC pipe.
5. A little heat from a heat gun greatly helps get stiff, white PVC hose over a barbed connector.
6. Effluent odors can permeate an inexpensive polyethylene holding tank. Test for this by first cleaning a section of the tank and then wipe the area with a cotton cloth. Take the cloth off the boat and then smell it. If head odor is present the polyethylene tank is permeable.
7. Adding some clear 1-1/2" hose at the through-hull allows you to see when you're done pumping out the holding tank.
8. Hiding the toilets water and effluent lines under the toilet's platform gives a cleaner look to the head. There's plenty of space under the platform to house the lines and it can be accessed from a hole made in either the engine room bulkhead or in the bottom of the stateroom's hanging locker.
In conclusion, new laws, and hopefully some enlightenment, motivated us to change how we operate Nellie's sanitation system. Now all head effluent goes into the holding tank. The holding tank can be emptied with either a shore based pump out or into the surrounding water via a through-hull. Looking to the future, Vermont's law may be an example of what we can expect next—there it's illegal to even have a hose connecting the holding tank to an underwater through-hull. Clearly we haven't gone that far with Nellie but that configuration is achievable by removing just a few hose clamps.
Thanks got to Bob White, Renegade #72, for his review and inputs.
No comments:
Post a Comment