Complete Rewire

Discussion in 'OnBoard Electronics & Controls' started by tWEEka, Aug 31, 2014.

  1. tWEEka
    Joined: Aug 2014
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    Location: Torquay, Devon, UK

    tWEEka New Member

    Hi, i recently bought an old snapdragon 26 in need of repair. so i got some help from friends and have fixed it up:), my problem now however is that one friend, who thought they were doing me a favour, ripped out most of the wiring thinking it an easy job to replace:mad::eek:. I have no idea where to start. I have never re-wired anything in my life and certainly can't afford a marine electrician to help me out! :?:Can anyone please direct me or help? Any diagrams etc would be great,
    Thanks in advance...
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    Well, damn, you're in a pickle aren't you. Rewiring from scratch requires some familiarity with electrical systems in general and practical experience in particular, so given your budget restraints, you'll have to learn this stuff yourself.

    The first thing to do is run through the archives at >< and see if they have anything that could help. A wiring diagram will not be much use, unless you understand what it says, so pick up a book or two on the subject, such as "the 12 volt Bible". Fortunately, your boat doesn't really have a very complex system, except to the uninitiated.
  3. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Can you afford at least someone to check the boat over and help you out? If so, I can recommend some friends in Totnes.
  4. AndySGray
    Joined: Jun 2014
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    Location: Cayman

    AndySGray Senior Member

    Don't think of it as a whole - Just wire one 'device' at a time.

    Get a good soldering iron, heat gun, snips and wire strippers.
    Cable ties, heat shrink and a waterproof pen and plastic tie on labels

    Picking the Port Nav light as an example

    The basic formula is P=IV -> Power (watts) = Current x Volts

    The old style bulbs were if memory serves 10W for smaller fittings and 25W for larger fittings so the currents for a 12V system are just under an amp for the small and just over 2A for the larger ones.

    Measure the cable run on a 26' boat I am guessing at 12' - YOU measure.
    which gives a 24' total (there and back).

    Use a table to get the correct wire size e.g. print this for offline

    or calculate online

    3% 8meters 12v - 17AWG is not common -
    So get a 12' length of 16 AWG (for 1A, 14AWG for 2A) two core boat cable and wire it back to the fuse panel.

    Ideally Crimp AND solder each of the end fittings (probably rings) and additionally protect with adhesive heat shrink.

    Probably take an hour for the first, 20 mins for the second and 10mins after that...

    OK so you have 4 sets of wires (Port Stbd Stern Mast) 2A on each = 8A total
    Wire all 4 reds to one side of the NAV switch - other side of switch goes to a fuse 8A (10A is nearest available) then to + on battery, blacks all joined to a common bus bar and then to battery. DO the calc again - may find you need 8 or 10 guage for that bigger load to the panel.

    Use proper marine cables if the boat is to pass inspection and get a copy of the rules for the boat safety scheme to make sure you don't forget e.g. a Battery Cut Off switch...

    Enjoy - he probably did you a favour in the long run - poor wiring is such a PITA

  5. WestVanHan
    Joined: Aug 2009
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    Location: Vancouver

    WestVanHan Not a Senior Member

    Do you still have the old wiring harness,etc?

    If you do- you can lay it back attention to where connections are,look at the wiring to see where it might have gone via lengths,colours,clamp marks on the wires indicating where it was fastened etc.

    I had to do this with a car,and it worked out.
  6. tWEEka
    Joined: Aug 2014
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    Location: Torquay, Devon, UK

    tWEEka New Member

    :DThanks for all your help, I'm not a complete novice so have decided to get a few books and learn how to do it myself. Thanks also for the links, very useful stuff! I'm going over tomorrow so will have a good look and maybe post some photos of what i need help with. The boat itself is in Avonmouth, so i would be very grateful if anyone could suggest someone close by to look it over?
  7. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

  8. WestVanHan
    Joined: Aug 2009
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    Location: Vancouver

    WestVanHan Not a Senior Member

    Tweeka read
  9. tWEEka
    Joined: Aug 2014
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    Location: Torquay, Devon, UK

    tWEEka New Member

    Sorry, I did read that post, but Totnes isn't all that close to Avonmouth & there are many other boatyards around the area, so I just wondered if anyone else was closer.
    I can't really afford to pay someone's travel fares! Didn't mean to offend!
    All the advice I'm getting is excellent, much more concise than when I've asked in shops/yards.
    The Snapdragon I bought for less than £3k so was initially very excited, not perhaps realising how much I needed to learn (or spend) in order to get her fixed up.
    All advice greatfully received!
    Last edited: Sep 2, 2014

  10. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    My advice is to do some paperwork first:

    1. Make a list of all electrical items you have and want to have on board. Specify the
    current/voltage requirements.

    2. Draw the wiring according to the approximate location of all items. No need to do that
    on scale, but specify the cable lengths. Pay attention to the location of switches.

    3. If there are any high current loads, determine the cable size based on current and

    4. Make a list of the colors you are going to use. Of course all negative leads are black,
    positive ones are red, for instruments you can use any color you want as long as you
    mark them in your drawing.

    Then post your paperwork here and add your specific questions, if any.....
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