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Earthing on boats

Discussion in 'Boat Electronics' started by davew, Oct 3, 2005.

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  1. davew

    davew Guest


    A friend that's just boaugh a canal boat is 'doing' it up and is worried
    about the
    electrics and has heard that boats use positive earth so he's asked me for
    I know about electronics & house wiring (well a bit anyway) but have never
    considered this on a boat where he'd like to have a computer TV etc....

    Now considering I was going to help him sort the electrics out what else
    should I know that's differant from 'Land' electrics I tried searching for a
    UK website but none found.

    Any pointers

  2. Usually, a boat has no "earth return", so the engine and electrics need a
    separate connection to the battery negative. The usual system is to have a
    distribution panel on which the positive is on the switch, indicator-lights
    and fuse (or contact-breaker) side, and all the negatives are fed back to a
    negative bus bar whic is connected to battery negative. The main switch is
    usually positioned close to the battery or batteries, and if a 2-battery
    system is used, a blocking diode is used so that the domestic battery can
    run down to almost zero, whilst you still have a full battery for starting
    the engine.

    If you can get hold of a copy of "The 12-volt Doctor's Handbook", this is a
    great starting point. Also Reading University's website used to have some
    great stuff on marine electrics, but I don't know if this is still the case.

  3. You might also want to try uk.rec.sailing for an answer.
  4. Guest

    Steel Canal boats should be wired with all switching in the positive
    line, an insulated negative return,but with battery negative bonded to
    the hull at one point..
    Blocking diodes for split charging are best avoided.
    Bear in mind that all wiring will be 12 or 24 volts and conductor
    cross sectional area is important and should be fully assessed based
    upon the length of the run.
    Methinks that you have not searched very much! There is a wealth of
    info out there on the web..
    uk.rec.waterways is the best group for asking questions.
    12v (typ) electrics on a boat are VERY easy to get wrong!!!!!!
    Your friends best bet is to get a good marine electrician to spec the
    system, then you could wire if you wish.
    Just my 2 pennorth


    Nb "Pound Eater" Glos+Sharpness Canal UK
  5. davew

    davew Guest

    This sounds like normal land electrics.
    I had a quick surfer a while ago but some info conflicted with
    other sites and what seemed to make sense.
    My fisrst confusion was the idea of positve earth and what happens when
    you tie up at one of those sockets along the canal.
    Cheers for that.
    Yes that's why I've done nothing, hands in pockets and all that.
    12V, lots of amps, water, diesel.... oil.......
    Well the boat ( I wish I understood more of) is around 53ft wooden
    boat made in the 1960s (not a narrow boat) and is still floating just.

    We got side tracked reading about the creatures that can eat away
    at the hull and getting the polarity wrong could mean losing the
    holding the thing together and how things differ depending whether you're
    in sea water or on the canel, fascinating stuff , I'd no idea of such
    bit different to what I'm used to such as wiring computers together.

    In the next few weeks it might be ready to be re-wired and/or checked
    before plugging anything in that's my plan but wasn't sure what I may face.
    I was hoping of a hayes type manual that they have for cars.

    I'm also hoping there's a free wi-fi hot spot somewhere along the regents
    canel unlikely I guess.

    Thanks for replying
  6. "one of those sockets along the canal" would presumably be 240v AC?
    So you can forget the hull for earth return.
    The only suppliers of "the 12-volt doctor's practical hanbook" seem to be
    in the US, but you could have a Google yourself. It is exactly what you
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