It’s doubtful that any watercraft has become more synonymous with Florida than the airboat. They have been the “transport du jour” into some of the state’s wilder regions for years, and are a major asset for law enforcement officers, aquatic weed control technicians, biological researchers, and search and rescue personnel; not to mention numerous civilian users.

It’s also doubtful that there is a noisier craft on the water.

When you stick a high-powered engine (whether it’s one designed to power aircraft or automobiles) in an unshielded position on the back of an airboat, and then have it drive a massive propeller that breaks the sound barrier at high RPM, you’re going to get noise. The basic physics put it in a different class than a cowled outboard engine with an underwater exhaust.

In past years, when Florida’s population was many millions lower than today, the noise—while annoying for some—was not a big deal. However, with the population approaching the 15 million mark, and with many residing near waterways, airboat noise has become a significant problem. In fact, according to several Florida Fish and Wildlife Conservation Commission (FWC) officers, noise complaints in some inland counties have skyrocketed in recent years.

In 2003 the Florida Legislature considered a bill to restrict airboat noise levels statewide to 90 decibels at 50 feet, but opted instead to give the FWC the rulemaking authority to adopt a uniform municipal code to address the noise level issue.

Under current Florida law, all vessels must be effectively muffled in a reasonable manner. In years past, law enforcement agencies have accepted flex pipe (an accordion-shaped metal hose that diverts engine exhaust to a point behind the airboat) as a reasonable muffling device.

Not anymore. The new rules will require all airboats to be equipped with automobile-type mufflers. According to a study conducted by Dr. Stewart Glegg, a researcher at the Florida Atlantic University Engineering Dept., mufflers can significantly reduce airboat noise when the vessel is operated at low to moderate RPMs.

The question is, will mufflers accomplish enough of a noise reduction to provide a solution to the problem? There is doubt in that area.

“I think the effects of adding mufflers will be minimal unless airboaters change the way they operate their boats,” says Capt. Ray Van Horn, a Tarpon Springs guide who has used airboats extensively in his business. “It can reduce noise at low RPMs, but there are other issues there that result in airboat noise at higher RPMs that are extremely expensive to address and correct. I have spent thousands of dollars on custom mufflers, carbon props, engine tuning and other tricks to get my airboat as ‘stealthy’ as an outboard engine, and have not really succeeded.”

As Van Horn’s experience has shown, and as Dr. Glegg’s studies confirm, engine exhaust is only a portion of the airboat noise equation, and not even the major one when the engine revs up.

“The prop itself generates more noise than the engine exhaust, especially at high RPMs,” Van Horn notes. “With the traditional wooden paddle prop you’ve got large blades that are breaking the sound barrier when you rev that engine up. Another noise factor is that the engine itself is not confined under a cowling, like an outboard, or under a hood like an automobile. Adding mufflers—airboats will require two—isn’t going to address either of these.”

Technology does presently exist to greatly quiet, but not totally eliminate, prop noise. It involves a pair of counter-rotating carbon props with multiple blades and multiple hubs. The system requires a complete re-working of the drive shaft system. But, it is hugely expensive. If demand was there, cowlings could be developed for exposed airboat engines, adding additional expense.

“There will be some airboaters who will be upset at having to pay up to $400 for a pair of mufflers under these new rules,” says Van Horn. “But, if that doesn’t reduce the noise level complaints and FWC decides to move to additional steps, those mufflers will be a drop in the bucket money-wise. You might see laws passed that would require a very expensive re-design of the airboat as we know it.

Some degree of compromise is needed, Van Horn says, and airboaters need to be conscious of how, where and when they are operating their boats. The FWC is currently developing guidelines for an Airboater Code Of Ethics that could greatly reduce the conflict between airboaters and the public.

FS