By Bob Humphreys
Over history, boat manufacturers, repairers and owners have used many inappropriate materials to conduct electricity. Finding those materials is often a challenge.
This particular one involved a 39′ sailboat made by a world renowned manufacturer. The retired owner was having difficulty starting the diesel engine in certain circumstances and was beginning to wonder if his choice for a retirement boat was a mistake.
This boat had two large 8D gel-cell batteries, a 150A 12V alternator and an aftermarket voltage regulator adjusted to prevent overcharging of the batteries. The batteries were connected to the engine through a ‘1, 2, both, off’ battery switch and when the engine was cold, it would not start using only one battery. When the battery switch had both batteries selected the engine would start without difficulty and the observed difference between single and dual battery cranking was a slight drop in cranking RPM.
The boat was two years old, and since new the starter had been rebuilt once and replaced, the positive cable from the battery switch to the starter had been replaced with one of significantly greater cross section, all with no change. My yard was storing this boat in anticipation of a sale in the spring because the owner just couldn’t rely on the engine.
During the winter decommissioning I went head-first into a locker to examine the back of the engine and found the ground stud on the engine bell-housing was hot enough to raise a blister on my hand. The engine manufacturer had installed a stainless steel 3/8 x 16 1″ long stud to use as a grounding point for the multiple grounds from the various electrical loads. The stud was threaded into the engine block and a nut was used to tighten the bell-housing, then the ground wires were placed on the protruding stud.
The resistance of this bolt caused a significant voltage drop which severely limited the voltage to the starter. I installed a #00 ground wire direct to the bell-housing next to the starter itself and ran the ground wire to a copper buss bar mounted on a nearby bulkhead and connected all grounds to the buss bar.
The owner removed the boat from the market and enjoyed it for many years. Stainless steel is a wonderful material for fastening in the marine environment and works well for clamping two things together but should never be used as a current carrying component.
Bob Humphreys received electronics training in the U.S. Navy, then worked as an electronic technician and test engineer in the semiconductor industry for 15 years. He built houses during the occasional lay-offs, and built and repaired boats for over 40 years until age diminished his ability to continue. He is currently working as a senior process technician for a medical instrument manufacturer in Maine.
He says he enjoys the Sherlock blog and is frequently reminded that there are simple answers to the most complex problems.
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