Earthing on a wooden boat.

[nashynetfit]

Dear Forum

I have recently brought an old wooden boat, however after trying start the engine, I cant get any life or even a spark.

I believ ethe problem lies with a combination of bad connections and also the fact that I cant seem to see any earthing wire from the batteries, which there are 2 main plus 1 at the rear end of the boat which runs an automatic bilge pump, again not earthed.

Can anyone advise where I would earth the boat, its a 2.5 bmc engine, and would teh same earthing place be suitable for a bilge pump, as this may be whats cuased the problem, as since this was installed, I believe wrongly, the engine won't start, but simply sparked once around the starter motor / igintion.

Many thanks for any advice.

 

[Tranona]

The earth should be the negative from the starter battery to the engine block - usually through one of the bell housing bolts. The positive goes through the switch to the starter motor. You don't need an earth for the bilge pump. It should be fed from a DC fused panel and switch which in turn takes its 12v power supply from your house batteries.

The non starting is probably poor connections or a knackered battery.

Sounds like you need an electrician to check it out for you - old wooden boats and electrics aren't good friends, particularly if people have "modified" them over the years.

 

[Dave_Seager]

Boat wiring is not earthed in the same way as a car as there is seldom a conductive structure that can be used (except possibly in a steel boat). Most electrical devices on a boat will be connected with both a positive and a negative wire. Usually the positive is fused and switched and the negative is permanently connected by they are exceptions. For example, my Princess has fuses in both the positive and negative wiring for every circuit.

In the case of an engine, you will usually find a heavy duty cable from the negative battery terminal bolted to the engine. There will also be a similarly heavy cable from the positive battery terminal to the starter solenoid. Other circuits on the engine may also be fed from the connection on the solenoid to the alternator, instrument panel and other ancillary circuits.

It is unlikely that that the negative cable has gone missing so it is probably a loose or damaged connection. If you saw sparks that would suggest a likely location to start checking. Be careful though because a short circuit on heavy, unfused cables can provide enough heat to weld metal and can give you a nasty burn.

 

[mitiempo]

Dave

In an aluminum or steel boat the structure is never used for earth. It's a good way to sink a boat. Ideally every DC switch is dual pole to switch both positive and negative. Isolation is the important thing on a metal boat.