Waste disposal systems layout and regs

Discussion in 'Boatbuilding' started by Charly, Jan 24, 2014.

  1. Charly
    Joined: Dec 2009
    Posts: 429
    Likes: 32, Points: 0, Legacy Rep: 377
    Location: st simons island ga

    Charly Senior Member

    Hey guys, I am at the stage of my catamaran build that I need to plan for the future installation of a head, sink , holding tank and disposal arrangement. I really appreciate all the knowledge, advice and ideas available here. Please feel free to critique my version.

    Here is my current plan/goal:

    Lavac manual toilet, plumbed directly into a holding tank. The tank will be located aft of the toilet. Straight line, no diverter valve.

    To evacuate the tank, it can be either vacuumed out dockside, or gravity drained overboard when appropriately offshore.
    As I see it, I have a few choices for the gravity drain. I could cut a thru hull next to the tank above the waterline and open a valve next to the tank to drain it (tank bottom would of course will have to be located high enough for proper flow),
    OR I could use a large dia flex hose that I could stick through an inspection port on the transom, let it trail out behind the boat, and gravity drain it that way. I like this option best, because I do not want to have any thru hulls above or below the WL that are not absolutely necessary. The only practical downside that I can see with it is maybe some smell from the exhaust hose when it is in the bilge and not in use.

    With the gravity drain, further flushing of the tank could be done with a deck hose connected to an on deck wash down pump (other than bilge pumps, hopefully this will be the only electric pump aboard the boat) The water supply for the head would come from a supply tank, that I could fill dockside or have the option to use raw water, by filling it with the washdown pump.

    I should mention that this boat will be chartered in some capacity, probably as a two or three hour sail, with six passengers when I need to scare up some money to pay for dockage, etc., BUT there is still the possibility that I will want to go for a COI at some point.

    One thing I am not clear on, is thru hull fittings and the US coasties with a COI: I know they spec metal only for below the water line, but what about above the waterline (WELL above the waterline like over a foot) And what would they say about a plastic inspection port on the transom?

    Heck, I haven't even broached the sink yet, but I may as well get it over with in this thread. I want to have a tiny little sink in the head, with a freshwater supply from a gallon jug, either with one of those hand pumps like that are used to meter out epoxy, or invert the thing and put a push valve like on a water cooler. Either way, be very stingy with it. No foot pumps etc to get in the way. Then drain the sink straight out and through the hull under the bridgedeck, just like the hatch drains that I have already had to put one for each hatch. Maybe even plumb the drain into an existing hatch drain if practical.... Would THAT fly with the coasties?

    The washdown pump would be under a step on the bridgedeck next to the hull with the head in it. I could mount a strum box on the intake hose and store it in there with the pump and washdown hose, and when I want to use it, just stick it down through the freeing port into the water (about 32" head). Maybe I could use the same arrangement for pumping out a shower sump in the head, by sticking the intake hose through the hatch and down ito the bilge in the head. This would be very occasional as there won't be more than maybe one month out of the year when the boat would be used overnight.

    Many subjects here, but any comments appreciated.
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 122, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    This is a simple system I have used with complete success. The diverter valve is mounted below waterline at the thru hull. When emptying the toilet, the diverter valve cannot pump out thru the diverter valve--- it HAS to pump into the holding tank.
    When the diverter valve is in the other position, it HAS to pump the tank contents out into the sea.
    This means the toilet outflow is blocked whenever the diverter is set to drain the tank, making it impossible to accidentally empty the tank directly overboard. In other words, the same hose is used both to fill and to empty the holding tank.
    There's no vented loop and therefore no chance of odors or leakage/back-siphoning (more of an issue with monohulls that heel a lot).
    Although I've never seen this setup excepty on my own boat, I used it for years with no problems. Unclogging is just a matter of reversig the flow for a moment.
    There doesn't appear to be a simpler setup out there. In legal terms, the toilet can't be pumped overboard inadvertently. It has to go first into the tank.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.