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September 21, 2007

Good Vibrations

We've all heard stories of seductive hulls and alluring engines-we want to know: Does boat noise raise fish?

Most big-game anglers I know swear certain boats raise more fish than others. Although there is no repeatable, scientific evidence to support the theory, Captain Pete Manuel, a hardcore North Carolina tournament competitor, is one of the believers.

Manuel recalls a former charterboat in Cape Hatteras, North Carolina, that was skunked constantly.

A day after running slightly aground on a shoal, he raised four blue marlin and finished the season with plenty more. When the boat was hauled that winter, a bent shaft was discovered and replaced. After the repair, the boat once again could not raise any fish.

Do some boats act as giant teasers-while others do not- because of the sound of trolling engines or the hull slicing through the water? Some say it is a mystical hum that mesmerizes fish like the Pied Piper. Others think it's an unusual noise that mimics baitfish. Whoever eventually figures it out is bound to make gobs of money. Here's what we do know.

Sound Science
Research has determined that billfish and tuna have small ear bones, or otoliths, relative to their overall size, so their sense of hearing is not nearly as acute as their sight. Instead of hearing with ears, they have lateral lines running down each side of their bodies. These fluid-filled canals have tiny, hair-like receptors that are highly sensitive to vibration at short distances. Sharks have similar features in the pores of their skin.

"Sound is tremendously important to fish," says Dr. David Ross, scientist emeritus at Woods Hole Oceanographic Institution. "Fish are sensitive to certain noises like other fish feeding or baitfish in distress. And we obviously know they're not always repulsed by boats. Besides, if fish don't like a certain noise, they can easily get away-it's a big ocean. I don't know if you can quantify it by saying twin or diesel engine noises are more attractive, but sound does travel well in the ocean, which is noisy anyway."

Hearing Aids
Some boats are said to spook fish less than others, according to those with a special appreciation for water flowing past a hull. Cold-molded boats crafted by custom builders in Carolina or South Florida are reputed to be the top fish-raisers. But Manuel also thinks new, inboard-powered, fiberglass boats exhibit a strong allure because their hulls, engines and bearings are tight, the running gear is properly aligned and the wheels are tuned.

For this reason Manuel, who has numerous tournament wins to his credit, routinely tweaks his 57-foot Island Boat Works sportfisherman. He changes cutlass bearings every year and has his wheels analyzed by Prop Scan computers. Afterwards, he checks for unwanted vibration by placing five-gallon buckets of water on the deck of the flying bridge and over each shaft. When the water in the bucket doesn't make rings, Manuel feels his boat is properly tuned to raise fish. He also carries spare wheels to every tournament, along with a computer printout showing the performance of each propeller. And when he's on the hunt, he frequently uses the engines' trolling-valve mode to increase the load and reduce excess vibration.

Although there is much we don't know about fish and boat noise, this much is certain: never mess with a streak. If your boat consistently raises fish, don't change a thing unless you absolutely have to. If you fly the skunk flag too often, however, there's always that soft sandbar.

Sounds Fishy
A product of optimism
More than a few companies make products that are purported to attract fish with sound. The Magic Sound CD ($10; www.starlures.com) duplicates the seductive, low-frequency hum of out-of-sync twin diesels. You just need speakers mounted in the hull. Or try dunking a sound-producing 12-volt-powered electronic fishing lure, such as the Mako Magnet ($350; www.makomagnet.com), to emit low-frequency sounds. Or just sing Jimmy Buffett tunes at the top of your lungs while ladling chum-$350 goes a long way at the bait shop.
- D.L.