There are a great many advantages to choosing a motorboat with an outboard engine, from the ease with which they can be accessed for maintenance to their ability to adjust the trim of your craft in shallow waters. However, these unique engines are just as vulnerable to mechanical problems as inboard engines and stern drives, and one problem in particular tends to be unique to outboard engines -- excessive vibration.
An outboard engine that vibrates violently when in use can lead to a number of problems, and can even damage the hull of your craft in extreme cases, so diagnosing and repairing the cause of the vibration as soon as possible is vital. The best way to do this is to call in a professional marine servicing company to inspect and repair whatever is causing your outboard to vibrate, but you can speed up the diagnosis by checking for the following common, vibration-causing malfunctions:
Propeller damage is generally the most common cause of excessive outboard vibration, and a propeller that has been knocked out of alignment by damage or wear will cause significant vibration as it spins. If you're feeling particularly suicidal, you can inspect your propeller while it is in motion, checking for wobbling that would indicate improper propeller alignment. A far safer course of action is to remove the propeller entirely and run your engine -- if the vibration stops, your propeller is is the culprit, and should be either repaired or replaced.
However, vibration caused by your outboard's propeller assembly may not be caused by the propeller itself, but by the shaft that spins it around during use. This shaft is fitted with a number of bearings that keep it aligned and stable during motion, but these bearing become vulnerable to wear after significant use, Check these bearings for significant signs of wear if you suspect your propeller shaft is causing your vibration woes.
Worn engine mounts
Since outboard engines are almost always fitted to a craft's hull after it has been constructed, they are not integrated into the hull, but are instead attached to the craft's stern using durble, flexible engine mountings. While formidable, these mountings can wear out over time, and worn engine mounts are another common cause of engine vibration. Check your outboard's mounts for visible signs of wear; damage to the hull around the mount attachments is a common sign of wear, especially in fibreglass craft.
If you discover worn engine mounts to be the source of the vibration, replacing them with new versions of your existing mounts is the most obvious solution. However, you might consider upgrading, as advances in engine mounting materials have created mountings that are flexible enough to absorb almost all of the vibration your engine normally produces. Ask your chosen marine service for advice and recommendations if you decide to upgrade your mounts.
Marine outboard engines are just as vulnerable to misfires as the engine in your car, and if one or more of your outboard's cylinders is repeatedly misfiring the problem can cause dramatic increases in engine vibration. Misfires usually cause the noise your outboard produces to change significantly, and can generally be heard even by untrained ears, although you may have to run your engine on dry land to confirm the problem.
Unfortunately, this problem can have an enormous variety of root causes, ranging from clogged diesel injectors to contaminated motor oil. Consequently, having your misfiring engine professionally nspected and repaired by a dedicated marine service company is generally the best way to deal with this problem, as attempting to tackle the problem yourself without extensive knowledge of marine engines can do far more harm than good.