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The Official Magazine of the Bluewater Cruising Association

Lessons Learned the Hard Way - Electrical Failure

Norm Cooper

Sarah Jean II
Saga 43
August 6th, 2015

Norm shares another valuable lesson learned from a major electrical system failure while on passage in the South Pacific.  Today’s boats having more and more electrical devices aboard.  Failure of the boat’s electrical system can create havoc ranging from spoiling all provisions in the freezer to the loss of key navigation and communication systems.


We had just started our passage from Niue to Tonga, a distance of 325 nautical miles.  The weather was stormy and overcast so the solar panels were not generating any power.  We thought it would be a good idea to motor sail for a few hours in the late afternoon to charge the batteries before going into the night.  We always like to have good battery reserves for operation of the radar.  We were surprised to see that the battery charge status did not improve after an hour of motoring.  A close inspection showed the alternator had no power output. It was not charging our batteries at all!

Our immediate response was to reduce our power consumption so we could save whatever juice still remained in the battery for navigation and communication.  We shut down the refrigeration and everything but essential navigation equipment. The remaining power in the 800 amp hour battery bank was adequate to get us to our landfall without incident.  Fortunately it was a short passage.  Upon arrival in Tonga the sun came out providing more than enough solar power for all our needs at anchor. Our problem was solved but only for the short term.


My assumption was the alternator had failed. We carry an identical spare. I would just swap alternators and then go for a snorkel. When this did not make any difference I concluded the problem must be a regulator failure. We carry a spare one of these as well. I swapped the regulator but this too made no difference.  There would be no snorkelling this day. The next step was to try replacing both the alternator and the regulator on the off chance both had failed simultaneously.  Still no output.  I then turned my attention to the wiring harness and checked that every connection was still in place. They were all intact.

When a major component such as the alternator (red colour on right side) appears to have failed, it may actually be the wiring connecting the alternator to other components that has failed due to corrosion.

When a major component such as the alternator (red colour on right side) appears to have failed, it may actually be the wiring connecting the alternator to other components that has failed due to corrosion.

This is when I gave up and called for help from other cruisers in the anchorage.  There were many volunteers with various degrees of expertise.  Most swaggered onto our boat confident they would quickly find the problem.  All of them departed mystified and with egos somewhat deflated.

I then decided to test the continuity of every single wire in the wiring harness, checking the resistance from one end to the other to make sure there were no hidden breaks anywhere. Mark Aisbett on s/v Merkava, a BCA member, helped me with this painstaking process.  We soon discovered that corrosion inside one little spade connector on one control wire was responsible for shutting down the whole system.  A new connector was crimped on and the problem was solved.

Mistake Made

I immediately assumed the charging problem was due to the failure of a major component like the alternator or regulator.  But these components are generally pretty robust.  The problem lay in the connectors.  The humid salt air in the tropics eats away at all electrical connections, particularly crimped connectors that are often exposed to the air.  This is the first thing I should have checked, not the last.

Lessons Learned

Always Suspect Corrosion in Connectors: Most electrical failures in the tropics are due to corrosion at the terminals, connectors or crimps.  Check these first before replacing components.

Have Diagnostic Tools: Have a good multimeter with a continuity tester.  Know how to use the ohmmeter function to measure resistance.  Have a long length of wire you can stretch throughout the boat to make certain tests.  Have several sets of alligator clips.

A good multimeter, such as this compact unit from Blue Sea, is invaluable when it comes to tracking down wiring problems related to corrosion.

A good multimeter, such as this compact unit from Blue Sea, is invaluable when it comes to tracking down wiring problems related to corrosion.

Contact Cleaning Solution & Fine Sandpaper: Surface corrosion that is invisible to the eye can build up on connectors and create resistance.  Often all that is required to solve a problem is to clean the contacts with spray contact cleaner and/or use a little fine sandpaper.

Carry Spare Connectors, Crimpers & Wires: Sooner or later you will have to replace electrical connectors on your boat.  Your spare parts box should have a large selection of proper marine grade connectors of every shape and size, a set of quality crimping pliers and a good supply of marine gauge wire of various gauges.  Corrosion can wick its way up inside the wire from the connector rendering much of it useless.  Then the wire run must be replaced.

Protect Against Moisture Penetration: If possible use heat shrink and/or connectors with integrated heat shrink covering to minimize moisture penetration.  A heat gun works great on shrink wrap provided your inverter can handle the load.


In this case a new connector, crimped onto the end of one of the alternator control wires, solved the problem.  The spare alternator and regulator went back into their storage boxes.

Have a Story?

We have all made mistakes and learned valuable lessons the hard way. Do you have a story you want to share with BCA members, so we can learn from your experience? If so, please submit it for publication in this column.  Thanks!

Send your story to with ‘OOPS!’ in the subject line.


  1. Hugh Bacon says:

    Hi Guys, yes electrical stuff is a major feature of a cruising boat and the means to charge large house batteries, in our case 800 amp hour capacity, needs more than solar panels and a wind gen both of which we were equipped with. Indeed our oversize but stock alternator (120 amp hour) was woefully insufficient and thus in our refit for cruising, besides the increase in house battery storage, we added a 300 amp hour truck type alternator. This beast became the heart of our electrical system as it minimized engine run time to charge batteries to 90%. I like to operate the house batteries between 70 % to 90% and with both alternators at work, we could bounce the house batteries back up in about 45 minutes and that is with regulators set to prevent excessive charge rates We rarely charged beyond 90% except by default if we had some motoring to do.

    All of the above to relate our serious loss of charging capability while in Tonga. The loss was entirely my fault! We had been hearing a slight grinding noise from the big alternator for a week or so and consultation with our fellow cruising wizards some with a lot more experience than I, we agreed it must be a bearing problem.

    Order new bearings about $60.00, three weeks delivery, freight about $600. With bearings in hand I removed the “beast” and lugged it over to a highly reputed Kiwi Mr Fixit. He installed the bearings and I reinstalled the alternator. I found it strange that the old bearings looked as new. I fired up the diesel and found no output from the alternator. To make a long story short, Mr Fixit had not installed the commutator correctly and it shorted out by contacting the wiring bundle at the rear casing. Now we needed a new commutator: read another three weeks and about $800.

    OK, we still had the stock 120 amp hour alternator so we cruised around Tonga as we awaited shipments from the US. Had to be careful not to run the batteries too low though or face hours of dieseling at anchor!

    Finally I got smart and began to look a little further. Using WD40 as a dye penetrant, I discover a hairline crack in the alternator mounting plate located on the lower front of the engine adjacent to the fly wheel. It was the two sides of the crack vibrating against each other which was creating the noise! Easy to fix. We pulled into a small yard which had portable welding gear and we put a thick metal plate overlapping the crack. Problem fixed at least until we got to the Canary Islands five years later. Then we did the same repair once again. Meantime, I had located a seriously competent all round mechanic at the local Moorings Base. Once the new commutator arrived, this chap installed it correctly ensuring internal clearances were right. Of we went to Fiji.

    OK so my message is similar to Norm’s. Fault analysis is an important skill which can save significant cost and time. Be careful about a seemingly knowledgeable fellow cruiser’s “expert” opinion. The most likely solution is often the simplest and most probably it does not lie with the actual piece of gear but rather a connection or something related to the assembly.

    Part of my professional background is in operational testing, specifically as a maintenance test pilot on RCAF fighter aircraft. This demanded a strong capability in fault analysis. I was absolutely mortified about my misstep in handling this incident!!

    Best, Hugh Bacon

    1. Rob McLennan says:

      Is this the Hugh Bacon who graduated from MRHS in Haney, B.C.? This is Bob McLennan, also a grad of MRHS. Our careers are similar, I spent time in the RCAF, learned how to fly, and then worked for Okanagan Helicopters in technical management, total OKie time was 27 years (easy time).

      Cheers, (Rob) Bob McLennan

      1. Hugh Bacon says:

        Hi Bob, yes it is I! Sorry it took so long to come across your comment. Drop me an e-mail sometime please when you have a moments. Hugh

  2. Bill Robinson says:

    Also, ALWAYS solder EVERY connection. And don’t use connectors if you can make direct solder joints – as when splicing or tapping into wires. I even solder light bulbs in directly when practical!

    I’ve had Scorpius almost 30 years now – including four years in the tropics and have had almost no electrical failures – and the only one I can think of that was due to corrosion was in some of the bilge pump wiring that was being continuously sprayed with salt water from a too-loose stuffing box.
    -Bill Robinson
    S/V Scorpius

    1. Ken Christie SV Blue Rose says:

      Bill, Norm,
      Yes, I soloder every connection , every terminal. It takes way longer. I have been criticized for doing so- by some of the great fixers. However the issue seemed to be that a soloder could easily be done too cold, be the wrong flux, , or in a lump instead of a hot taper and not shrink wrapped causing copper metal fatigue with vibration. These fears are from the occasional poor craftsmanship, and not a reason to avoid a conductive molecular metal bond. (Just saying how I feel here)

      In a pinch one can even soloder an old corroded copper blackened wire to get one home- a crimp would never work there.
      Also, all those spade and other connectors vibrate and get looser, they oxidize & such. It’s ok to compress them by .5mm and plug unplug plug to scrape the contact surfaces clean.
      When faced with any suspect whirring, I start off as Norm recommended, test every wire. But my backup solution is Tag those wires with clearly written tabs (white electrical tape & black marker) draw out a schematic, then unhook that suspect one and run your own direct bypass new clean full length wire.

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