Making Sound Choices
Pay attention when listening to the music of your boat.
Anyone familiar with music knows “Good Vibrations,” a tune from the legendary Beach Boys, which aptly described the nascent feelings of a young generation on the move. But the bewildering vibrations your boat can develop following an accidental grounding or collision with a submerged object are nothing to sing about. Things happen out on the water. You miss a buoy, or enter a strange channel on full-moon low tide and suddenly there is a swath of mud or sand in your wake. If you stop in time and scour your way to deeper water you’re lucky. But whenever your props hit real estate or solid debris, the story can have a different and usually more expensive ending.
With a stern drive or outboard boat inspecting the prop is simple; just tilt up. Inboards are a different breed, however, because the propeller is only one part of the drive system and stray vibrations from a damaged propeller quickly lead to other findings. With any engine, sudden vibrations mean you should slow it down until the problem is isolated and solved. With inboards, that usually entails having a diver pull the prop after limping back to the dock, or a boatyard visit for a haul out. The latter is my first choice when possible because it is the best thing you can do. Depending upon what you hit and how hard, a diver may be all you need. But unless you have a spare prop for the diver to swap, you will have to wait for the prop to be reconditioned at a reputable shop and have the diver come back and reinstall it. If you are traveling, you are likely to lose a day before you are back underway. How you spend your time, though, often brings different results.
While the diver can be your quick-change artist, a hard hit will require a more thorough inspection of the boat’s underwater gear, including the other propeller (if your boat has twin engines), the rudders, the shafts, the shaft zincs, the struts, the through-hulls, and the bearings. But unless the shaft is obviously bent like a hockey stick, or the strut bolts are loose, it is not always easy for a diver to make assumptions about the condition of this equipment, particularly if the water is murky and the bottom of the boat dirty. Plus, you are relying on one set of eyes to perform this inspection. If there are any lingering issues, they may suddenly reveal themselves in the form of other, new vibrations the next time you throttle up, like a shuddering bowrail, sensations that seep through your Top-Siders, or worse case, the propeller shaft breaks and your newly reconditioned NiBrAl takes a final spin to the depths below.
Here’s why a haulout is a better way to go. Besides the underwater gear mentioned earlier, the propeller shaft is connected to a coupling at the rear of the engine at the transmission. Some boats also may have a resilient insert sandwiched between this coupling and the reverse gear. Aboard many boats, the transmission has a set of mounts connected to the stringer system. The engine has its own set of mounts, also secured to the main stringers. These fixtures generally have a rubber or synthetic insert to absorb vibration. All of the mounts allow the engine, transmission, and shaft to remain in alignment for smooth operation. The instant the prop made contact with whatever it hit, the impact created a domino effect with the relationship all of this equipment has working together to provide that smooth transfer of power.
You also should recognize that all of these components are age-related. Just like you go for a physical to check your health, when was the last time you had an engine alignment, the strut bearings replaced, or the propellers balanced as part of your routine maintenance schedule? If it has never been done, chances are you have become accustomed to the normal vibrations and habits your boat has accumulated. This may explain why after having a propeller reconditioned the engine does not turn to full rpm. Causes could be that the engine is out of alignment or the shaft has a slight bend and is pinching the strut bearing. There are many possibilities, but more than likely it’s time for some maintenance.
This is why I opt for a haulout after a good grounding. It is the perfect time to give the boat a powertrain-component overhaul. Get the boat out of the water and inspect the bottom and running gear carefully. Put a couple sets of eyes on the hardware and look for things. A small hairline crack in the shaft can lead to a big problem. Tour the inside of the engine room. How are the stuffing boxes? Severe leakage is another tip the engine alignment is out of whack. Look at the engine mounts. If they are painted, is there any rust nearby? This could mean the metal parts are moving and grinding against each other.
Running aground or hitting a log is part of boating. If it happens to you, take it as a minor inconvenience on the way to making your boat more seaworthy. You may not be able to sing about the vibrations, but you will have a good story to tell when you get back to the dock.
This article originally appeared in the July 2017 issue of Power & Motoryacht magazine.