Pre-Purchase Inspections
March 2010 - Air in Fuel

If there's one system that simply has to be reliable aboard any cruising vessel it surely must be the fuel system. When compromised or inadequate the results can range from a nuisance to catastrophic.

Imagine this scenario (this happened to me once), you are approaching the entrance to the Cape Cod Canal and, thanks to a broken alternator belt you're running about 45 minutes behind schedule. That means, instead of transiting at slack water as you had intended, you will be powering against the formidable tidal induced current for which this waterway is known. You're anxious to get to your destination, the Maine coast, to begin exploring its many harbors, rivers and off shore islands so you decide to press on. Besides, your engine has ample power for overcoming any current, or so you think.

You set your course and throttle up to overcome the effects of the tide, enjoying the scenery as it passes by. Within a few minutes of entering the Canal, however, you notice a barely perceptible change in the engine's note and as you glance at the rpm gauge your heart sinks. It's usually rock solid but now instead, it's fluttering and sinking slowly. You throttle back and the engine seems OK but as you reapply power the engine stumbles and almost stalls. You send your mate to the engine room to switch the tandem primary filter to the standby element, certain that the one you are operating on is clogged. After the switch over you tentatively advance the throttle, but the same symptoms persist and again your heart sinks. You manage to keep the engine from stalling while maintaining headway until you reach the marina at the east end of the Canal. You breathe a sigh of relief as you make your lines fast and then immediately head for the engine room without bothering to shut the engine down. It's hot and noisy, but that doesn't matter, you have to determine how your hitherto trusty engine and fuel system let you down; you carefully look at the primary filter bowls, searching for the cause of the problem, dirt, asphaltine, water…but nothing is there, just clean fuel. The recording vacuum gauge also mysteriously remains in the green zone or low vacuum. Then you see them, small bubbles escaping out of the coalescer cone inside the filter's settling bowl, a stream of saboteurs on their way to wreak havoc on the otherwise orderly fuel injection system.

Although it's not often thought of as a "contaminant", air can have as detrimental an effect on diesel engine operation as water and debris. In the example image from this month's ad, taken aboard a new vessel undergoing a SDMC Pre-Purchase Inspection, air bubbles are compromising the operation of this 52-foot motoryacht's engines (remember, it's a new boat). Among others, the defect was brought to the attention of the selling broker and corrected before the buyer took delivery. The culprit turned out to be a coupling whose threads were incompatible.

If you're interested in finding out more about Pre-Purchase Inspections like the one described above, system inspections, vessel selection assist, the Captains' Club (simply click on these words to be taken to the relevant sections of this website) or other services offered by Steve D'Antonio Marine Consulting, email or call 804-776-0219.