Diagnosing the 30A drain

So at the end of our Easter weekend sailing we had a problem.  Our solar array was designed to recharge the batteries whilst looking after the power requirements while sailing.  On the trip back up at the Orwell, it looked like somewhere we were losing about 30A at 24V. This meant we were drawing power out of the batteries even in bright sunshine. If that kind of power usage was within the boat then it would likely be generating a lot of heat.

We set about understanding the cause of this on our return.  We had already established that it as the second circuit in our bank which controlled winches and the bow thruster.  All of these seemed to work fine which added to the confusion.  By disconnecting the individual elements, we were able to trace the power loss to the bow thruster.  This is located under the fore peak berth. Opening this up we found a few issues. Firstly, there had clearly been some heat on the positive terminal. 20190504_130923The wiring had melted.  We had this once before in the aft cabin where the wiring for the  davits came into the boat.  On this occasion it was some corrosion within the wiring that had caused the problem.

Our belief is that this stems from well before our ownership of the Moody.  A long time ago, a dehumidifier had been left running on the boat and had caught fire.  This caused damage to the floorboards, galley and headlining.  We imagine that putting this out required a fair amount of water and that when the boat was awaiting repair this water was left to stand with quite a bit of our low down electrical wiring in it.  As the wiring corroded it became less efficient creating heat and then melting parts of the wiring.  This could be rubbish but seems a plausible explanation. So the heat may be the cause of our loss of power but it didn’t explain why this was happening even when the bow thruster was not operating.

We disconnected the negative wire from the bow thruster and there was no drop in the amps going out of the boat. Oh dear. So the amps are going out through the bow thruster into the water. Fortunately, this circuit is only switched on when we are sailing and not when we are berthed or anchored so at least we haven’t done too much damage to our neighbours but this could also explain why our anodes were eaten through within fifteen months.  May be this had been going on for longer without us noticing.

Potentially we could have tried to repair the existing bow thruster drive unit but with our plans, this didn’t seem sensible, not least of all because cost wise a rebuild would probably have been a similar cost to a new one. 20190504_130710There was also quite a bit of surface rust of the bow thruster too which in an area that is mostly dry seemed strange – maybe reinforcing our theory about the fire.

There was some concern as to whether the drive unit would detach from the housing or whether we would have to come out of the water to do the work.  Fortunately the combination of corrosion X, WD40 and a little time worked wonders and the bolts could be undone to take out the old unit.  The new one was a lot of money but I guess now we have peace of mind.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s