Size of grey/black tanks needed for protected seas?

Discussion in 'Boat Design' started by fouxfleur, Jul 10, 2007.

  1. fouxfleur
    Joined: Jul 2007
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    fouxfleur New Member

    I am in the middle of refitting a 35' steel ketch to do a round the world trip. We are anticipating that in certain places (such as protected areas) it is obligatory to have a grey water tank and black water tank. Does anybody know in general if there are general minimum tank sizes that are required or have any experience or advice in this matter?

    Thanks very much.
  2. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    The regulations I know (several states in the US) all regulate discharge, actually "no discharge", rather than tank size. The point being that you can have whatever size tanks you want, so long as you don't discharge into protected waters.

    Calculating how much volume is needed for X days and X people is simple but not necessarily easy, because of variables in personal metabolism, diet, body size, climate, etc. There is an excellent discussion of the subject here. It's worth reading all the way through:
  3. safewalrus
    Joined: Feb 2005
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    safewalrus Ancient Marriner

    Really its a case of how big is a bucket? how big do you want it to be? how much can you carry? how many will be using it? how far is it to the next discharge point?
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    FAST FRED Senior Member

    Very few places need the Grey water held , "no discharge" usually means No treated black water.

    Simplest method of extending the range is to use an RV style setup , where the head products drop straight down into the holding tank.

    Sorta hard to retrofit , bur MOST of the water in a black tank is from flushing. A good RV unit will flush on 1/2 pint a time , so 20 gal is a LOT of time and use.


  5. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    In my RV I have a black water and a grey water tank. The black water is 35 gal the grey is 42. The one that takes the shortest time to fill is the grey water. Every thing from the sink, shower, what have you, except the toilet goes to the grey water. If we follow our normal routine, daily showers, washing dishes, cooking, etc., two of us can fill the grey in two days. If we are very frugal, and use the rv parks showers we can make it four days until the grey is full.

    The black tank takes more than a week to fill.

    When dry camping (no hookups) we go to frugal. We use very few dishes or pans that will have to be washed. We take sea showers (wet down, turn off water, soap down, rinse off). On a boat at sea you could wet down with salt water and then rinse with fresh. The ships I was on in the Coast Guard, were plumbed with seawater pipes so you could do that, if the ships evaporators stopped working, which they did quite frequently.

    Now for the latest. Some new houses being built are installing a grey water tank, which is plumbed to the toilet and used for flushing. You could certainly do this on a boat or RV. Saves on fresh water if you use grey water to flush.
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