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Spin doctors

Propeller repairmen keep your boats running smoothly.

By TERRY TOMALIN, Times Outdoors Editor

© St. Petersburg Times, published April 12, 2002

Propeller repairmen keep your boats running smoothly.

TAMPA -- Spring is great for fishermen but even better for propeller repairmen.

"This is our busiest time of the year," said Bob Musselman, owner of Admiral/C&B Propeller. "A boat propeller is like a muffler on a car. You usually don't deal with the problem until it is too late."

The difference is when your muffler goes bad, you still can drive slowly to the auto repair shop. But what do you do when you lose your propeller 20 miles offshore?

"Propellers are out of sight, out of mind," said Musselman, who repairs about 20,000 of the propulsion units each year. "But it is one piece of equipment that you cannot do without."

Humans began using propellers around 100 B.C., but they didn't become widely used for propulsion until the invention of the steam engine. On ships, propellers replaced sails about 100 years ago.

"But in the last couple of years, the number of different types of propellers has risen exponentially," Musselman said. "Today it is more of a "niche' market ... bass boats, flats boats, etc., all have different props."

Musselman's shop works on everything from $25,000 props for mega yachts to "throwaway" propellers for flat-bottomed johnboats.

"One of the things that many people wonder about is whether they should get an aluminum or steel prop," Musselman said. "The difference is in performance. It is like driving around with good tires on your car. You can feel the difference."

A steel prop costs about $300 to $400, an aluminum prop about $100.

"Aluminum props are sacrificial," he said. "If you hit something or lose it, it is not a big deal. A steel prop will give you better performance. But if you hit something, you can seriously damage a lower unit."

Boaters who move to Florida after spending time on the lakes and rivers up north may wonder what you can hit in the Gulf of Mexico.

"Lots of things," Musselman said. "Sandbars, oyster beds, crab traps ... too many boaters use their boat propellers as depth finders."

If you own a flats boat, a stainless steel, four-blade prop is the way to go.

"It will get you up on a plane and run in 6 inches of water like it is supposed to do," he said.

But boaters always should carry a spare, even if it is just a cheap, reconditioned aluminum prop. "After all, would you drive around in a car that doesn't have a spare tire?" he said.

How do you know which is the right prop for your boat?

"The propellor should make the motor run at the maximum rpm range at full throttle," Musselman said. "The first thing I ask people when they have a propeller problem is, what kind of rpms do you get at full throttle?"

Determining the right match can be a complicated process.

"You have to have an accurate tachometer and know the motor's maximum rated rpm range," he said. "You can then adjust rpm by changing diameter, pitch, cupping, the number of blades or some combination of all four."

Still, most of Musselman's repairs come from simple collisions.

"As long as there is beer and low tides, we will stay in business," he said. "If the water is low late on a Sunday afternoon, we know we will have a busy week."

Propeller basics

PITCH: Measured in inches, pitch is the theoretical distance the propeller would travel in one revolution.

DIAMETER: The size of the "hole" the propeller creates in the water. Usually determined by measuring from the center of the prop to the end of one blade (the radius), then multiplying by two.

CUPPING: A small flare in the trailing edge of a propeller blade that decreases rpm. Increases efficiency by reducing cavitation and ventilation. Except in very slow applications, like sailboats or work boats, a cupped propeller will usually work better than one that's not cupped.

UNDERPROPPED: Not enough pitch and/or diameter causes too many rpms at full throttle. Results in poor fuel efficiency and speed and may result in motor damage.

OVERPROPPED: Too much pitch and/or diameter causes not enough rpms at full throttle. Results in poor hole shot and efficiency and may cause motor damage.

-- Source: Bob Musselman, Admiral/C&B Propeller

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