"Can you hear me now?" isn't just a famous commercial catchphrase – it refers to most powerboats, too.
Sound levels on boats from center consoles to trawlers can be downright uncomfortable, ending casual conversation and making cooperation between crewmembers difficult.
Just how loud is too loud? And is there really anything you can do about it? Listen up, because there may well be.
Companies have introduced a bevy of new products in recent years to combat noise, including high-tech insulation, add-ons for your engine and exhaust system – even special sound-reducing paint.
LENNY RUDOWNoise from the hull slapping the water will travel throughout the boat, but even this can be mitigated.The result is that, while every boat's needs may be different, there is an increasing number of options for owners to explore at all price levels.
FEEL THE NOISE
Sound levels are commonly measured in decibels, expressed as dB-A. Most boats produce 55 to 65 dB-A at idle, and somewhere between 80 and 100 dB-A while running. On boats with open, exposed helm stations, wind alone accounts for much of the elevated sound level, sometimes as much as 30 or 40 dB-A.
But these numbers can be deceiving because decibels are measures in a logarithmic scale. Scientifically speaking, the decibel scale actually measures ratios between power, sound pressure, voltage and intensity, and they relate to fancy terms like phon and sone. In plain English, on the decibel scale, a mere three-decibel increase is approximately a doubling of sound levels.
How loud is loud? A quiet conversation produces around 50 dB-A. Chainsaws usually come in around 110. Sitting 50 feet in front of the speakers at a rock concert exposes your ears to around 130 dB-A. At a distance of one foot, 150 dB-A is potent enough to shatter your eardrum. And at 194, particles in the air start to compress, and you get a sonic boom.
OSHAThe sound levels on some boats often exceed OSHA's maximum standards.Ten years ago, some of the worst offenders of ears in the marine world were large, two-stroke outboards. A pair of 250-horsepower carbureted motors could produce up to 110 dB-A – as much as a chainsaw grinding its way through oak. Cruising could be unpleasant at best and damaging to your ears at worst. Consider that the Occupational Safety and Health Administration (OSHA) standards require that no worker be exposed to 90 dB-A for eight hours at a time without ear protection. Workers exposed to 115 can be exposed for only 15 minutes.
Where does all this sound come from? As you'd expect, much of it is airborne, simply traveling through the air from your engine, transmission, gears and exhaust. But another major source is structural transmission, coming from vibration transferred throughout the boat via the hull, deck and other major structures.
The sound of water pounding against the hull, for example, eventually reaches the ears of someone sitting 20 feet above in an enclosed flying bridge and of someone lying in a berth inside the cabin. The same goes for engine sound, because engines are affixed to the main structural component of the boat. Remember your high school physics class? Sound travels through solids even better than it does air, so while closing the cabin door may cut off airborne noise, it won't eliminate the structural variety.
3MThinsulate, from 3M, is easily added to most engine rooms. But it is not cheap.BAD VIBES
Fortunately, both of these can be combated. Retrofitting is possible in most cases, although the boat's original design and construction play a huge role in sound reduction. Cored bottoms and fiberglass-foam sandwich construction, for example, damp both airborne and structural sounds, because they provide a natural insulation barrier. Boats that are built more solidly also tend to have lower sound levels, simply because fewer parts creak and vibrate when traveling through seas.
Despite these facts, the largest contributor to sound on a boat – and probably the largest area you can impact – is the engine. Stern drive and inboard owners have several options to consider. But the most obvious solution is also the best one: Add acoustic insulation to the engine room or engine box.
Warning: You can't use any old insulation for a boat. First, it must be fire retardant (remember, this is an engine room we're talking about). Second, it needs to be hydrophobic, which is a fancy way of saying it won't absorb water. If it does hold moisture, a mildew explosion will be just over the horizon. Third, marine insulation has to be non-linting. Essentially, this means tiny bits and pieces won't fall off of it as the boat pounds through waves. Those are the "musts." Ideally, marine insulation will also be thin and light, so it can be used to line a compartment without taking up much space or adding much weight.
ROOLS, PANELS AND PAINT
Since marine insulation must do a lot more work within much tighter parameters than standard home insulation, the stuff isn't cheap. Take 3M's Thinsulate marine acoustic insulation, for example. It is hydrophobic, lightweight, non-linting and offers excellent sound absorption. It is sold in rolls and is just one or two inches thick (both sizes are offered). Yet all that costs about $2 per square foot for the inch-thick version and about $3 per square foot for the two-inch version.
If your engine room is 10 feet wide, 15 feet long and five feet tall, that means you'll spend about $800 for inch-thick insulation or about $1,200 for two-inch insulation. Installation is fairly easy, because Thinsulate can be easily cut, stapled onto bulkheads or stringers when wood is present, or glued in place with 3M adhesive if you need to affix it to fiberglass surfaces. But if you ask your yard to do the job, you can expect cost to go up by about 50 percent, for a final tally between $1,200 and $1,800.
LENNY RUDOWDry-exhaust systems are louder than wet-exhaust systems, but neither is problem-free.
Another acoustic-insulation option is to install panels, such as those available from Soundown. These have a fire-retardant polyester layer with a PVC barrier and a Mylar exterior vapor barrier. Panels are available in many sizes, weights and shapes, costing from $4 to $6 per square foot.
Or you could go the viscoelastic route. Confused? I was, too, until I saw Silent Running's coatings at a trade show a few years back, where it won an innovation award. Silent Running is essentially a rubberized paint; it converts mechanical energy (read: vibrations) into heat, by absorbing the vibrations (read: sound) and dissipating them across the entire coated surface. This is a cost-effective option for do-it-yourself types, because a five-gallon bucket of Silent Running SR1000 coats 200 square feet and costs about $240, for a total material cost of $1.20 per square foot. Of course, you'll also need the painting tools to apply it, and this "paint" must be built up in layers, so it's labor-intensive. But if you have your boatyard do the work, it will cost at least twice as much as the materials alone.
Outboard-boat owners have few options for lowering the volume, but most modern four-stroke outboards are incredibly quiet already, with sound readings of less than 60 dB-A at idle and in the mid-80s at cruise. If you own an old-tech two-stroke, adding insulation isn't an option in many cases, because there simply isn't room under the cowl. But on some models, wrapping the inside of the cover with a thin layer of simple foam insulation can help. About $40 will get you all the insulation and the adhesive you need to secure it in place, and the job can be done by just about anyone. One note of caution: When adding insulation under an outboard cowl, don't block the engine's air intake or allow the insulation to get near any moving parts.
VIBRATION ELIMINATION
What about all that structural noise? In some cases, such as water noise, insulation will have a damping effect, at least in the areas where it is applied. But when it comes to engine-produced vibration, the motor mounts and shaft have direct physical contact with the structure of the boat, so an entirely new tack is needed: soft mounts and bushings.
GAFFRIGClamp-on exhaust tips are easy to install and effective for inboard gasoline engines, though they are also pricey.Aquadrive, which supplies some high-end boat builders such as Pearson and Fleming, manufactures several vibration-control devices. One is a coupling that uses rubber bushings to allow movement between the engine and shaft, eliminating the transfer of vibrations from the shaft into the structure of the boat. In its shaft incarnation, the same principal can also be used with inboards, jet drives and even thrusters.
The second part of the Aquadrive system consists of a CV joint, and the third piece of the vibration-free puzzle is the company's "soft" motor mounts, rubberized mounts which absorb vibration before it is transferred to the boat's structure. Put them all together, and you'll get a vibration reduction of 50 to 90 percent. The downside? The entire system has to be installed by professionals, and can cost as much as $3,000 for small engines (in the 100-horsepower range) and $12,000 for large engines (up to 450 horsepower.)
EXHAUST OPTIONS
Naturally, your engine's volume level also depends on the exhaust system. Because the exhaust system is attached to the boat's structure and plumbs directly to the engine, it produces both types of sound. Marine diesel inboards commonly generate in excess of 100 dB-A, and even after quieted down with acoustic insulation and structural vibration control, the exhaust system still generates a lot of sound.
Generally speaking, the larger a muffler is, the better it is at sound reduction, because it reduces the exhaust gas velocity – and the higher the velocity, the louder a sound it makes when exiting the system. Unfortunately, in most installations, muffler size is dictated by the amount of available space, not sound-level requirements.
Another contributor to sound level is pressure; sudden pressure changes are loud, but they can be mitigated with a bit of backpressure in the system. Many boats have water-lift mufflers, which use a combination of minimal backpressure and water-cooling to reduce the gas's volume and regulate its pressure. If your boat has straight exhaust or a dry-exhaust system, you may be able to lower the decibels with a wet-lift system – but there's a downside. Improperly designed or installed wet systems can allow water to back-flow into the engine and, in some extreme cases, can even sink the boat. The short story: This isn't a job most people should handle on their own. And the installation is labor-intensive. Plan on spending thousands of dollars and, in the case of large inboard yachts, tens of thousands.
Underwater exhaust would seem to be an obvious answer, but often these systems can actually boost sound levels by causing new vibrations via turbulence, or by putting exhaust gases within reach of the boat's props. In short, a boat must have been originally designed for underwater exhaust.
In some cases, specialized mufflers can minimize sound. When it comes to gasoline-powered inboards with minimal factory-installed muffling (think: rumbling speedboats), simple clamp-on exhaust tips can work wonders. Many models are available from high-performance companies like Gaffrig, Corsa, and CMI, and modestly competent boaters can install them. Expect them to reduce sound levels by eight to 12 dB-A, a significant difference especially when you consider that many boats in this category create well over 110 dB-A and break 100 even at idle. But, like most parts of a go-fast boat, these add-on exhaust tips are big, shiny and expensive. Prices range from $500 to $1,200 for a single unit.
Then again, what fun is it to ride around on a boat that's as loud as a screaming chainsaw? If you're sick and tired of yelling, take action and make your boat sound like a winner.
Lenny Rudow was senior technical editor for Boating magazine for more than 10 years, and is currently the electronics editor for Marlin and GoBoating magazines.