How can I reduce my boat engine’s noise?

Outboard engine

I have a five-year-old inboard/outboard MerCruiser 135. Is there something I can do to reduce the engine noise? Maybe soundproofing the engine compartment?
—Larry Schmidt, Bass Lake, Ont.

Sure. Chris Poole, co-owner of Buckeye Marine, in Bobcaygeon, Ont., suggests lining the inside of the engine box with a high-density sound-reducer such as acoustic foam. (Check stereo shops, or marine or auto supply stores for products, and make sure the foam is safe to use in gas engine compartments.) “It works very well,” says Poole. That is, assuming the racket isn’t caused by a problem with your boat.

A loud engine could mean a malfunctioning exhaust system, says Rob Davidson, the coordinator for the Marine and Small Engines Program and Apprenticeship at Georgian College, and owner of Rob’s Marine Service in Orillia. For instance, the exhaust bellows may have become disconnected, and aren’t correctly diverting the exhaust underwater.

As well, make sure the boat’s running at the proper RPM. “If somebody put the wrong prop on the boat, the engine could be revving way higher than it’s supposed to,” says Poole. If the engine’s revving at more than 4,800 RPM, the prop should be replaced with one that has a higher pitch. Keep in mind, your engine may sound loud because it’s relatively new. Some newer fibreglass boats don’t have much in the way of sound-absorbing wood, says Poole. Noisy? Yes. But it won’t rot.