water tank volume calculation

Discussion in 'Powerboats' started by Armada01, Aug 31, 2016.

  1. Armada01
    Joined: Jan 2010
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    Armada01 Junior Member


    I'm writing a design specification for a 60ft motor vessel to be used for charter and need to calculate the volume of :

    -fresh water tanks
    -grey water tanks
    -black water tanks.

    Anyone know how much fresh water* is used per person on a charter yacht (not super high-end), as well as disposed on an average by person as grey and black water?

    *Freshwater would be used for showering, brushing teeth, dishwashing, food and drink preparation as well as laundry and vessel cleaning (weekly thorough cleaning will be in port obviously)
  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

    A little more info is required
    Are the heads going to be freshwater?
    If they are freshwater, what type of system are you using for the toilets, ie vacuflush, regular water fill and flush etc
    Heads can consume a lot of water. Salt water heads minimize freshwater capacity but odor control of the black water tank can be an issue.
    Laundry, if this is done away from port, then you will have to determine what your washer uses per cycle. Are you washing the guests clothes or just linen
    Are you using an automatic dishwasher or hand washing them

    As a charter boat, your guests will not expect to ration the water so you should consider a freshwater maker then you will not have problems
    Are you able to discharge black water overboard when away from port, grey water when away from port, dishwasher and laundry water overboard when away from port?
  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    In addition to seconding Barry on the need for some more information to answer, I would say that many of the questions that a design can raise are answered in the regulations that the ship must comply. Find out what rules the ship is required to meet and you'll probably find many answers.
  4. Armada01
    Joined: Jan 2010
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    Armada01 Junior Member

    Tx Barry for your feedback,

    The heads would be salt water. Using fresh water seems insanity IMO. It'll be a vacuflush system for the toilets as a manual pump will require to know how to use it, and most charter guests are not familiar with life aboard.

    Laundry will be primarily for clothes washing. Bed linen will be done weekly, during the day in port. Not that much clothes will be washed either. It's primarily the ones that are sweaty and smelly and for which the guest has no double and the crew clothes (2crew) also day will do their washing primarily during the day in port between charters.

    For dishes, an automatic dishwasher will be used. However, latest models are often more frugal than hand washing in terms of water consumption. So that shouldn't really add to the sum total IMO.

    I will also carry a freshwater maker, but these use a lot of energy (fuel) and I want to keep the cost of fuel to a minimum, not knowing where fuel costs will go in the decade ahead. Therefor I aim to have a decent fresh water carrying capacity, but on the other hand limited in volume since a huge water tank will quickly increase the vessels displacement, raising fuel consumption again, as well as the vessel's sales price, which is often calculated by yards based on displacement , not LOA.
  5. Armada01
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    Armada01 Junior Member

    Tx TANSL,

    I've posted a question regarding this in the Class Societies forum.
  6. Armada01
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    Armada01 Junior Member

    to Barry,

    I forgot to mention: the vessel will operate mainly in coastal waters, so no possibility to discharge any water at sea.

  7. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Minimum of 10 gallons a day per person, not including laundry. And this just with a quick shower twice aday. Dishwasher alone is a major consumer on a boat. Might want to use disposable plates in your circumstance. ; )
    Most people aren't used to rationing water, so with out a water maker, you need very big tanks, far more than fuel.
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