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Avoiding Engine Damage
How a little vibration can turn into big problems

By by Hugh Carroll
Posted Tuesday, August 21, 2007

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A simple and often overlooked essential aboard, marine engine mounts protect the structural integrity of your boat. The more powerful your engine, the more vibration it creates and the more potential damage it can cause. Engine mounts literally stand between the engine and a cracked hull.

Likewise, flexible disc couplings protect your drive train. The engine shifts from vibration and dynamic movements, particularly propeller thrust, while the drive shaft does not. This can generate huge problems. Flexible disc couplings take up the vibrations/movement that occurs where the transmission meets the drive shaft.

Knowing about the different kinds of engine mounts and flexible disc couplings available, and how to maintain them, can save you time and money and keep you afloat. All too often, owners remember to care for their engines and completely forget to service the foundations.


In the past, it was normal for engines to be mounted directly to the hull or frame. As boats grew in size, so did marine engines and this practice eventually caused irreparable damage to the craft. Naval architects and engineers were able to isolate the vibrations and noise produced by more powerful engines with shock-absorbing mounts.

When selecting an engine mount, pay attention to who makes it and what its applications are. Several manufacturers primarily make mounts for industrial use and later moved their products into the marine industry.

There are many more forces affecting a boat than a stationary industrial site. On the water, your boat and engine are subject to thrust, port-to-starboard and bow-to-stern movements, violent weather and large waves. Make sure the mounts you have on your boat are specifically designed for marine conditions.


Flexible disc couplings play a substantial role in protecting the drive train. Not only do they isolate vibration from the motor to the shaft, they reduce it from the shaft to the motor. Providing a physical brake between the engine and the shaft, couplings also stop electrical current from flowing between the two. This prevents electrolysis and corrosion.

Some couplings are designed to break if the boat hits something and the shaft stops. They will shatter first to help save the transmission. Without a transmission, you're dead in the water.


Engine mounts and flexible disc couplings are available in countless configurations and made out of thermoplastic or a combination of metal and rubber. If you regularly replace the metal/rubber variety, you shouldn't have any issues.

But beware, the marine environment is harsh. Metal is subject to rust and rubber hardens over time. Rubber can also deteriorate from UV rays and common engine room fuels and chemicals. They need to be replaced or the vibrations will start making their way into the hull or drive train.

If frequently replacing mounts and couplings sounds like a real pain, there is a thermoplastic alternative. Many thermoplastic versions are extremely resistant to UV rays, fuels, chemicals, freshwater and saltwater. They won't rust like metal or harden and deteriorate like rubber. With some brands, if you install the mounts and couplings correctly, you'll never have to replace them.

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