antonywardle Posted April 30, 2020 Share Posted April 30, 2020 Hi everyone I've been trying to track down 12 volts that shows up on the multimeter when I go from the + on the battery to the hull. (Hull is a plate boat). I've disconnected everything in a few attempts to sort this out. The only thing I can think of is that the engine boat to the transom aren't insulated. Could this be the cause? Does an outboat been to be insulated from the hull? I have the backing board between the engine and the transom but the bolts simply bolt on. thanks Link to comment Share on other sites More sharing options...
Renegade460 Posted April 30, 2020 Share Posted April 30, 2020 They have just used the hull as an earth return. The engine electrics will be earthed through the motor as well, motor won't be insulated from hull. Problem with running a hull earthed system in the possibility of electrolisis and the resulting corrosion. 1 Link to comment Share on other sites More sharing options...
antonywardle Posted April 30, 2020 Author Share Posted April 30, 2020 so the fix will be to insulate the bolts? Link to comment Share on other sites More sharing options...
dmck Posted April 30, 2020 Share Posted April 30, 2020 No... what you are seeing is common to every aluminium boat I have seen. It is not a problem unless the hull IS USED as part of an electrical circuit. EVERY electrical device on the boat should have a +ve and a -ve wire going to it.. The -ve wire MUST be connected back to the battery either directly or by a joining to another cable. Using the body as a part of the circuit is OK for cars... but not for boats. 2 Link to comment Share on other sites More sharing options...
zmk1962 Posted April 30, 2020 Share Posted April 30, 2020 41 minutes ago, dmck said: It is not a problem unless the hull IS USED as part of an electrical circuit. EVERY electrical device on the boat should have a +ve and a -ve wire going to it.. The -ve wire MUST be connected back to the battery either directly or by a joining to another cable. @dmck has said it MOST succinctly. 100% agree. If you want further confirmation please look at the post by "kmorin" on the following link - he goes to great lengths to explain exactly what our Don has summarised in 3 lines... http://www.aluminumalloyboats.com/viewtopic.php?f=3&t=2260&view=previous Do earth the -ve of the battery to the hull (similarly the motor will have a -ve attachment somewhere on the head and then to the hull through the mounting bolts). Do NOT use the hull as part of the electric circuit (run a separate -ve and +ve wire to every device). With this set up, if a stray current does appear, it would follow the path of least resistance (the dedicated -ve wire) back to the battery rather then use the hull. Cheers Zoran 2 Link to comment Share on other sites More sharing options...
antonywardle Posted April 30, 2020 Author Share Posted April 30, 2020 Ok I have bus bars that are insulated from the hull and that's where all of my devices go to. and from there back to the battery. So @dmckin my case, I'm good? @zmk1962, thanks for that link, I'll take a look. 1 Link to comment Share on other sites More sharing options...
zmk1962 Posted April 30, 2020 Share Posted April 30, 2020 (edited) 1 hour ago, antonywardle said: I have bus bars that are insulated from the hull and that's where all of my devices go to. ...as long as every device has its own -ve and +ve path back to the battery (ie. no device uses the hull as a -ve path). Cheers Z Edited April 30, 2020 by zmk1962 1 1 Link to comment Share on other sites More sharing options...
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