Ben was living the dream with his family while on vacation in southwest Florida. Cruising on one of the many twisty mangrove-lined rivers, he glanced at his chart plotter and saw he should have four feet of water beneath his bay boat, which only draws 18 inches or so when running. Suddenly, a loud bang shattered his reverie, and Ben quickly realized his boat had hit something hard. He shut off his outboard and tilted it up to reveal his stainless steel prop’s blades were severely bent, and his lower unit’s skeg had lost its tip. When he restarted his engine and put it in gear, there was a vibration severe enough he was afraid of damaging the outboard’s gears, so he called for a tow since he didn’t have a spare prop. The $850 tow charge plus a $500 repair bill for the prop put a dent in his vacation budget, and then there were the lost days on the water while he sorted it out.
Ben learned four lessons that day:
Should You Fix or Replace a Damaged Prop?
A boat’s propeller is one of the most crucial parts of a boat motor. When its pitch and diameter are dialed in, and it’s in perfect shape, a boat’s performance is maximized. But when the prop is even slightly damaged, it causes a drop in efficiency, and the vibration it creates can damage an engine, so it’s essential to address any imperfections as soon as possible.
There are a few different ways to proceed with a damaged prop. If it’s only slightly dinged, an owner may be able to fix the problem themselves. If it’s more seriously damaged, take it to a prop shop for an estimate. The general rule is that if the repair costs more than 50 percent of the prop’s value, it’s probably best to get a new one. If the worst-case scenario happens, make lemonade by exploring if another model prop or different pitch and diameter can improve your boat’s performance based on your usage. An excellent resource for finding the ideal match for your boat is Yamaha’s Prop Selector, which considers performance goals and factors in your input about the top rpm your motor is achieving.
‘Tis But a Scratch
An owner can perform a couple of fixes to props with minor damage. One of the most common problems occurs when a prop barely contacts a hard surface like the concrete on a boat ramp. If you can feel tiny nicks or burrs on the prop’s outer edge, it might not seem like much, but even minor imperfections can affect performance. Fortunately, this fix is easy; you’ll need a course file, a fine file and a metal brush. The brush is used to clean the files to ensure no shaved metal is in the grooves. Then, take the course file and use gentle upward strokes on the blade’s edge until it feels smooth. Lastly, use the fine file to hone the surface further. The goal is to correct imperfections while removing the least amount of metal.
Fixing a Bent Prop Blade
Bent blades are a bit trickier, but if small, they can often be bent back into shape using two adjustable crescent wrenches. The first wrench is used on the nearest unaffected part of the blade to hold it in place. The second wrench goes in the middle of the damaged area. Tighten both to increase leverage and prevent slippage. Apply pressure to the wrench on the damaged section until it matches the rest of the blade’s curve.
Sometimes, the bent blade tip of a stainless steel prop is curled, and this damage can sometimes be pounded out with a softer brass hammer that won’t mar the surface. Unless bends are minor, consider this a temporary fix to get you through the weekend until you can get it professionally repaired.
When to Take a Boat Prop to a Professional Repair Shop
Some repairs are beyond the scope of even a savvy DIYer. If a prop has a broken blade, it can likely be repaired by fabrication, as can a broken skeg. Badly bent blades are usually fixed by placing them in a metal template form and banging them back into shape with one of up to a dozen hammers. Usually, the blade is heated (annealed) to make it more malleable before hammering. Professional prop shops also machine-balance a prop when repairs are done to ensure it won’t cause a vibration.
Some shops use sophisticated equipment like a Helix pitchometer powered by TrueProp® software to precisely document a prop’s exact shape and flaws before and after the repair.
Periodically Check Your Prop
Occasionally, taking your prop off to closely inspect it is a good idea. Imperfections like small cracks may not alert you with apparent symptoms but can cause a future catastrophic failure. A common problem is fishing line wrapped around the prop shaft, which can damage seals and reduce a prop’s ability to spin freely.
How to Tell if a Propeller is Hurting Performance
Knowing how your boat performs when it is in tip-top shape is a valuable measuring stick for determining when there is an issue. The most telling performance parameter is a boat’s top speed and the rpm it reaches. Make sure you compare apples to apples by replicating the weight aboard when you initially tested it. Also, allow for slight variances due to weather and sea conditions. If you reach the same speed, the problem isn’t significant, or a repair was successful. But, if the engine fails to push your boat at the same speed or the rpm is different than you previously recorded, there is a problem. Although it could be for reasons other than the prop, that’s a good place to start to avoid future problems.
Back to Blue Life
Ben learned four lessons that day:
- Charts aren’t 100 percent accurate and may not reflect recent shoaling. Underwater hazards aren’t always noted.
- When cruising in unfamiliar waters that are shallow and known to have underwater obstructions, such as oyster bars or stumps, use an aluminum prop, which is cheaper and transmits less force to the gearcase in the event of a strike.
- Always carry a spare prop. To get more utility out of it, choose one that is slightly different and is better at tasks like carrying heavier-than-usual loads.
- Get a boat tow service membership. You’ll save money even if you only have to use it every few years.
Should You Fix or Replace a Damaged Prop?
A boat’s propeller is one of the most crucial parts of a boat motor. When its pitch and diameter are dialed in, and it’s in perfect shape, a boat’s performance is maximized. But when the prop is even slightly damaged, it causes a drop in efficiency, and the vibration it creates can damage an engine, so it’s essential to address any imperfections as soon as possible.
There are a few different ways to proceed with a damaged prop. If it’s only slightly dinged, an owner may be able to fix the problem themselves. If it’s more seriously damaged, take it to a prop shop for an estimate. The general rule is that if the repair costs more than 50 percent of the prop’s value, it’s probably best to get a new one. If the worst-case scenario happens, make lemonade by exploring if another model prop or different pitch and diameter can improve your boat’s performance based on your usage. An excellent resource for finding the ideal match for your boat is Yamaha’s Prop Selector, which considers performance goals and factors in your input about the top rpm your motor is achieving.
‘Tis But a Scratch
An owner can perform a couple of fixes to props with minor damage. One of the most common problems occurs when a prop barely contacts a hard surface like the concrete on a boat ramp. If you can feel tiny nicks or burrs on the prop’s outer edge, it might not seem like much, but even minor imperfections can affect performance. Fortunately, this fix is easy; you’ll need a course file, a fine file and a metal brush. The brush is used to clean the files to ensure no shaved metal is in the grooves. Then, take the course file and use gentle upward strokes on the blade’s edge until it feels smooth. Lastly, use the fine file to hone the surface further. The goal is to correct imperfections while removing the least amount of metal.
Fixing a Bent Prop Blade
Bent blades are a bit trickier, but if small, they can often be bent back into shape using two adjustable crescent wrenches. The first wrench is used on the nearest unaffected part of the blade to hold it in place. The second wrench goes in the middle of the damaged area. Tighten both to increase leverage and prevent slippage. Apply pressure to the wrench on the damaged section until it matches the rest of the blade’s curve.
Sometimes, the bent blade tip of a stainless steel prop is curled, and this damage can sometimes be pounded out with a softer brass hammer that won’t mar the surface. Unless bends are minor, consider this a temporary fix to get you through the weekend until you can get it professionally repaired.
When to Take a Boat Prop to a Professional Repair Shop
Some repairs are beyond the scope of even a savvy DIYer. If a prop has a broken blade, it can likely be repaired by fabrication, as can a broken skeg. Badly bent blades are usually fixed by placing them in a metal template form and banging them back into shape with one of up to a dozen hammers. Usually, the blade is heated (annealed) to make it more malleable before hammering. Professional prop shops also machine-balance a prop when repairs are done to ensure it won’t cause a vibration.
Some shops use sophisticated equipment like a Helix pitchometer powered by TrueProp® software to precisely document a prop’s exact shape and flaws before and after the repair.
Periodically Check Your Prop
Occasionally, taking your prop off to closely inspect it is a good idea. Imperfections like small cracks may not alert you with apparent symptoms but can cause a future catastrophic failure. A common problem is fishing line wrapped around the prop shaft, which can damage seals and reduce a prop’s ability to spin freely.
How to Tell if a Propeller is Hurting Performance
Knowing how your boat performs when it is in tip-top shape is a valuable measuring stick for determining when there is an issue. The most telling performance parameter is a boat’s top speed and the rpm it reaches. Make sure you compare apples to apples by replicating the weight aboard when you initially tested it. Also, allow for slight variances due to weather and sea conditions. If you reach the same speed, the problem isn’t significant, or a repair was successful. But, if the engine fails to push your boat at the same speed or the rpm is different than you previously recorded, there is a problem. Although it could be for reasons other than the prop, that’s a good place to start to avoid future problems.