Salvador Mejia maneuvers a 600-pound yacht propeller onto a stand using a hydraulic lift. He hoists a 20-pound hammer over his head and strikes one of the blades. Mejia, a propulsion reconditioner at Frank & Jimmie’s Propeller in Ft. Lauderdale has decades of experience. He can see and feel the smallest of dents with his hands.
Even so, this part of the repair that requires a hammer may take him an hour or an entire day.
Yacht captains understand that myriad things can whack a prop out of balance, said Brandon Cooney of Lauderdale Propeller Service. Electrolysis, cavitation, a bottom bump, even driving over a submerged log or coconut can cause vibrations, fuel inefficiency and mechanical issues.
“Just five one thousandths (.005) can make a prop out of balance,” Cooney said as he pointed to rows of new, slightly bent and mangled propellers during a walk through the shop in Ft. Lauderdale.
But captains may not realize just what goes into making that prop turn smoothly again.
“We understand the need for a quick turn around, but it can be a tedious process,” Cooney said. “We do old-fashioned blacksmith work here.”
It takes a craftsman to repair a propeller, agreed Jimmie Harrison of Frank & Jimmie’s, and that’s why it takes anywhere from two days to two weeks for the entire process.
“It’s a misconception that the computer fixes the prop,” Harrison said. “It doesn’t. It measures the prop.”
The process of fixing an imperfect prop begins by taking it off, either in-water or during a haul-out. Commercial Diver Services in Ft. Lauderdale dives to remove damaged props, and owner Geno Gargiulo takes many emergency calls, including a recent one from a yacht more than 40m in length in the Bahamas that was preparing for an owner’s party. Surprisingly, it took three days to remove the damaged prop. (The topic of removal and installation are extensive enough for another article.)
Back to the prop shop for the repair: first anti-fouling coating is removed. Since megayacht props are usually made of bronze or nibral (a nickel, bronze, aluminum alloy) they weigh hundreds of pounds and take the repair crew some effort to move with hydraulics and forklifts.
The real repair begins when the prop is placed on a computer stand for assessment. Using a variety of manual measuring tools, craftsmen like Mejia scribe each blade with lines at 50, 60, 70, 80, 90 and 95 degrees from the hub.
Now it’s the computer’s turn. Mejia will guide a Prop Scan or Hale MRI (Measurement Recording Instrument) to take readings along his prescribed lines and several computer screens worth of data are computed. With these numbers, Mejia isolates and marks raised and lowered spots along the scribe marks.
Next, he moves the prop to pitch blocks, which support the blades, chooses the appropriate hammer — covered either with rawhide, copper or aluminum — and pounds out the damaged areas. Big dents will require big hammers and big swings.
When he thinks he’s close, Mejia will move the prop back to the computer to see how near to allowable measurements the dings are. Then it’s back in the blocks for more hammering. He continues the sequence until the prop is within ISO class tolerances. It is important for all the blades, whether there are three, five or more, to be nearly identical.
“It’s like swimming,” he said. “If one hand is cupped and the other is flat, you don’t swim straight.”
During the repair, if any chunks are missing from the prop, it is sent to the welding department to make them whole again.
Toward the end of the repair the prop is subject to a few more checks, said Robert Abrahamsen, Frank & Jimmie’s production manager.
“The geometry of props is really complex, but two types of balance testings confirm the work,” he said.
The prop is hoisted onto a stand that holds it vertically, the way it will be installed on a yacht, and set to spinning. The technician can see if any of the blades is not perfect in weight.
“The static balance test uses gravity to allow the heavy blade to swing to the bottom,” Abrahamsen said. “And the dynamic balancing machine spins it to show any imbalance.”
“People ask for dynamic balancing because they think it’s a computer repair,” Harrison said.
But prop shops use the machines just to take readings; the work still lies with the techicians, he said.
“We use the MRI for about 80 percent and dynamic is about 10 percent,” Harrison said.
Eventually, the propeller moves to the grinding, polishing and buffing room.
“People think polishing is sign of good prop, but it’s just the last step,” Harrison said. “They like to see shiny props, but what they can’t see is the balance and the pitch.”
At the time of propeller repair, captains choose between their priority in reference to cost, accuracy and time, Harrison said. It can take two months and more money for a yacht to have a custom or specifically designed prop. And less time and money (therefore, less accuracy) for a standard factory prop or a previously used prop that is repitched or reworked.
Propeller experts offer captains, engineers, managers and owners a few insider tips to prevent and prepare for prop work:
Plan for delay. Be prepared for potential difficulties removing or repairing a damaged prop, Cooney said. You know when a job starts, but not when it will end.
Understand the paperwork. Captains make better choices when they are familiar with class requirements and understand their prop’s repair paperwork, said Chris Brown, general manager and president of High Seas Yacht Service, in Ft. Lauderdale.
“It helps if captains understand the different ISO class levels and how to read a routine scan report,” he said.
Captains are usually given an initial assessment of a damaged prop that lists averages of pitch and radius measurements on each blade. Then the propellers are typically repaired to ISO 484 tolerances for class S or class 1.
Class S is the most precise. Class 1 works for a 10-knot boat or one running at slower shaft speed. Class 2 would be for a tug, Brown said.
“If a yacht is Class 1, we don’t want them to go to sea trial and wish they had requested Class S,” he said.
Captains should be aware that the American Bureau of Shipping (ABS) and Lloyds have implemented survey requirements for when a vessel is hauled for propeller work, Brown said.
Keep records. Crew may save time and money by maintaining original records, as well as subsequent repairs throughout the life of the prop.
“Captains need to tighten up the transfer of information with the movement of crew and records,”
said Dean Gualillo, outside sales at Frank & Jimmie’s. “Often in yachting we see transient crew, and it might be the old crew that knew the prop history.”
And crew need to understand that proper documentation and assessments may be required by an insurance company before a repair is started.
“If insurance is an issue, the captain, engineer and management company need to understand what is needed to qualify for coverage and claims and how to expedite that,” Gualillo said.
Consider spares. There are two schools of thought on spare propellers, said Charlie Boyd, sales manager at Frank & Jimmie’s.
“A yacht could have identical spares that are rotated and left on while the other is repaired,” he said. “That means initial high cost, but the replacements will run identically. Or cheap spares, like your space-saver tire on your car, which will have less performance and need to be replaced with the repaired props.
“Really, you always need spares because you will need a prop at the worst possible time and place, when there is no facility and you’re stuck,” Boyd said.
Typically, storage space is an issue so most yachts keep spares on land, although some long-range vessels have designed onboard storage for props and hardware.
“Good boats have spares because time is money,” Harrison said. “We hear, ‘I have a charter that starts …,’ so it is a smart move, moneywise. They are the most likely thing that can be damaged and can put a trip out of business. Props are very necessary.”
Monitor the ride. Captains and engineers should be aware of vibrations, sounds and efficiency onboard. The engine load and propeller relationship is key, said Troy Erb, owner of Wildcat Propellers in Chesapeake, Va.
“A lot of captains overlook this because they never run at wide-open throttle,” he said. “The prop, when loaded, should be 96 to 97 percent on load and not red-lined at 100 percent. The vessel will achieve better efficiency and your engines won’t wear as fast.”
And consider the prop when adding a substantial load. The weight-versus-horsepower equation changes and the prop may need to be adjusted as the waterline has changed and the vessel sits wider in the water, Erb said.
Abrahamsen recommends that captains also keep up on zincs.
“I see this often, one side’s prop has more electrolysis,” Abrahamsen said. “Check for a bad ground or if zincs are missing. If it’s the side closest to dock, check for a shore-power issue.”
Even with all of this information, Gualillo simply said, “don’t forget about your props.”
“Usually yacht captains and engineers are very savvy and keep watch, but sometimes they have to push a trip through,” he said. “And during that, props get overlooked. Yachts need a smooth, quiet ride that doesn’t upset the wine glasses. You don’t want to feel or hear them.
“But these invisible, hidden props are the unsung heroes that can be the source of downtime.”
Dorie Cox is associate editor of The Triton. Comments on this story are welcome at firstname.lastname@example.org.