ALTERNATOR WOES

In previous blogs we have told of problems with bolts breaking and constant repairs needed to the alternator support system. In this one Vince explains exactly what the problem turned out to be and how he is attempting to fix it.

The engine that I put into the boat was a Yanmar 3GM30F which came with a 55Amp alternator. Soon after acquiring the engine I realized that for the electrical demand on board, a larger alternator was needed. A professional, who spoke at a meeting of the Boat Builders Association suggested that I install a 120A alternator available from “Powerline” with one foot support and one pulley to drive it. (remember this).

About half way down the Erie Canal the “foot” broke off the alternator casing. This “foot” was part of the alternator casing and was the only support attaching the alternator to the engine block. The other side of the alternator was attached to a bracket for tightening. Fortunately I had brought a spare alternator (same make and model as the broken one) which I was able to re-attach. Meanwhile I arranged for the broken part to be welded back on to the original which now became my “spare”.

Part way down the Hudson River the bolt attaching the alternator to the engine sheared off. I replaced it. In the ICW the bolt sheared off again. Another replacement was done. Then the foot of the alternator itself snapped off again! At this point we knew that we had to have a mechanic come out to the boat and do a thorough diagnosis to determine what was wrong. He told me that anything over 100A should have two belts and be two footed. He suggested that I contact a Yanmar dealer and get a bigger Yanmar alternator with this type of support system which is designed specifically to “fit” with the Yanmar engine. Fortunately I had the original Yanmar 55A two footed alternator with me and he was able to professionally install it. This got us safely back out on the ICW again and I made arrangements with a Yanmar dealer in Charleston to install an 80A alternator when I arrive there.

This has been an expensive lesson that I am sure others could learn from Preferably, alternators on boats should have “two feet” regardless of size. Since manufacturers spend millions designing systems with components compatible with each other, it’s only logical that wherever possible you purchase an alternator made by the same manufacturer as the engine and designed to “fit” it.