You know how beat you were after just a few hours in your boat last weekend? Was it the result of eyestrain from all the glare on the water? Not a chance, especially with those cool shades that set you back a couple of bills. Maybe it was from dining all weekend on burgers and colas? Naaah.

It was noise. Pure and simple ' the sound of sound. Too much noise can cause all sorts of seemingly unrelated physical and emotional symptoms, as the crews of wartime bombers discovered. Not only is noise exhausting to your body, but it can make you cranky and irritable, reduce the quality of your vision, impair your judgment, and slow your reaction time. It can even make you seasick (the word noise comes from the Greek word nausea, and we all know what that is). Noise such as the hearty rumble of a big V8 may sound cool, but it's definitely not good for you.

Noise is measured in decibels on a scale from 0 (the least perceptible sound to the human ear) to 180. The threshold of pain is around 120 decibels or about the same as a rock band. A three-foot chainsaw measures about 100 decibels, average city traffic is 80, and normal conversation is about 50. Even more important to keep in mind is that with every increase of 10 decibels, the sound is considered to be doubled, so 80 decibels is twice as loud as 70 decibels.

It isn't unusual for inboard or sterndrive boats to reach levels in the 90 to 105 decibel range, which easily exceeds the Occupational Safety and Health Administration (OSHA) labor regulations. However, pleasure boating isn't one of the areas it regulates. And while you may not have to worry about OSHA, noise can still be unhealthy to your budget as well as your ears. The state of Maryland, for instance, passed a law establishing a maximum of 90 decibels for boats on any waterways there, and many other boating areas have even tougher noise laws that can earn you a hefty fine if you exceed them.

It's a fact that most small boats, inboard and sterndrive alike, have poorly insulated engine boxes. A layer of thin foam on the inside or upholstery on the outside does not count as quality sound insulation, although it is better than bare fiberglass. What you really want to do is examine where the noise is coming from, and then eliminate it.

Let's start with the engine exhaust, particularly for waterski or performance boats, because straight-through pipes are going to put out plenty of sound. Adding a muffler (or replacing your old one) will knock down most of that sound to an acceptable level. Centek Industries (800/950-7653), for example, offers the Vernatone inline muffler in several sizes specifically for boat exhausts, and there won't be a noticeable loss of power due to back pressure from the muffler.

An engine also exudes an immense amount of noise (pistons, valves and miscellaneous clatter) through the steel or aluminum block, so you want to contain that noise inside the engine box. Noise Reduction Enterprises has prepackaged kits that are ideal for insulating engine boxes (either inboard or sterndrive), such as the I/O Basic 24, which includes 24 square feet of one-inch-thick sound foam, reflective foil seam tape for clean, professional edges that block out moisture and fumes, spray adhesive, and special fasteners. While there are many variables, you can easily expect the kit to reduce your sound by 10 to 20 decibels, cutting your sound by a quarter or a half. And the price is reasonable ' the I/O Basic 24 kit costs $98.75.

To make the 'cocooning' of your engine complete, locate and plug any openings in the engine box that can allow sound to escape. If you can seal the engine compartment from the rest of the bilge, that's even better. Obvious openings are control cables such as those for the throttle and shift, fuel hoses, and bilge pump plumbing. One boatowner found another culprit: the plastic soft drink holders that were recessed into the engine box. While they were quite convenient, unfortunately they also allowed a lot of sound to escape.

Use rubber or vinyl molding to seal the engine covers or hatches, and you may want to add positive latches to hold the covers in place. Out-boards are relatively quiet, but a panel placed at the forward end of the motor well will bounce a lot of the noise away that can otherwise carry into the cockpit. Even snap-in cockpit carpet can help block noise emanating from the bilge area, particularly if it has a heavier pile than the usual felt-like carpeting. In the cabin, you can use carpet with a noise-barrier underlay available from carpet stores.

Since noise can be transmitted either by air or vibration, you should see if your engine can be remounted on soft or flexible mounts to reduce the transmitted vibration noise. A 'hard' mounted engine is going to transmit considerably more noise even with an insulated engine box than a 'soft' mounted engine.

By the same token, inboard owners should remember to check their prop shaft to make sure that it is properly aligned. A misaligned shaft will add a considerable amount of both airborne noise and vibration.

Engine air intakes can also be noisy, especially with carbureted engines. By facing your air intake ducts aft, you can redirect some of the intake noise away from your cockpit area. Even better, consider looking into a sound-deadening air filter for your carb intakes that will reduce the noise at the source.

An afternoon spent insulating your engine can pay big dividends in reduced noise levels. Afterwards, you'll discover that silence really does make your boating time golden!

July 2001