Steve Fennell
Oops. What’s the number for Mercury Marine?
Words by Steve Fennell
Hitting a rock with your prop while underway is a sudden incident that gets your immediate attention. That deadening “thud” (or sometimes it’s a series of “thuds”) is not the most pleasant sound. In many cases, the condition of your prop, which just took one for the team, will not be so pleasant either.
It’s a given that Canadian lakes or rivers will take pieces of aluminum or stainless steel every season, leaving your prop with some battle scars such as burrs or a bent blade. Although sometimes the damage is minimal, other times it’s not. A little TLC is often required.
“I see little nicks or burrs on props all the time from recreational boaters,” says Chris Croswell, owner of the Prop Shop in Armstrong, BC, located about an hour from Shuswap Lake. “In most cases, they get away with running a prop in this condition but at some point, the shaft bearing or the splines (where the prop is fitted) will be set off balance and eventually it can damage other parts as well.”
Mr TinDC
The splines on a prop shaft.
Even though these little nicks, burrs or minor bents on blades look minor, tiny bubbles can form, thus creating air on the blade face that results in cavitation. Consequently, you’ll experience decreased performance with higher rpm (especially on straight runs) and poor fuel efficiency.
Overtime, due to the “un-true spin,” the hub of the spline (where the prop connects on the shaft) will eventually wear. A good way to check the condition of the spline is by wiggling the prop back and forth. If it doesn’t have a nice, snug fit and it’s loose, the prop and spline need to be replaced.
In a worst-case scenario, and it all depends on how fast and hard your prop hits a rock or other unforgiving obstacle, there will be damage to the prop shaft.
“While not that common, it does happen and the shaft can be expensive to repair,” says Croswell. “These days, however, the newer shaft designs have a lot more resistance when it comes to hard impacts.”
Some warning signs include vibrating or even a harmonic sound, especially with inboard engines with longer prop shafts, such as those that power wakeboard boats.
Balb Allen
Taking care and knowing water conditions is ideal to maintain a prop’s efficiency and performance.
Damage Control
Being below the water’s surface, props are pretty much out of sight-of-sight, out-of-mind. Whether or not you do hit something, it’s always important to do routine inspections throughout the season. Closely examining the blades, ensuring a snug fit, and removing the prop to examine the condition of the splines, are all essential to ensure an efficient-running lower unit.
“It’s also a good idea to inspect the safety systems such as cotter pins or lock washers,” says Croswell. “Sometimes the nylock nuts (that are commonly used) can wear, so it’s best to make sure the plastic is always in good condition. This is also when you should look for other obstructions such as tightly wound fishing line, as it can sometimes cut or tear the prop shaft seal over time.”
When it does come time to repair a damaged prop or other components, the cost, of course, always reflects the damage. Quite often it’s more cost effective to repair rather than to replace.
“Just about anything is fixable,” says Croswell. “However, when there’s damage close to centre of larger pitch props, then it’s usually best to purchase a new one. Or, other times, less expensive props are not really worth fixing. But if you have a good quality prop, then we suggest that it be repaired. It’s also important to realize that when a prop is repaired, some thickness on the blade is always lost. Over time, the surface will just get thin beyond repair.”
Taking care on a lake by learning about local water levels, where shoals are, and simply understanding “where not to go” is the first step to preventing a damaged prop. Additionally, a routine inspection of your lower unit – whether or not you hear that “thud” – will ensure top performance and reliability all season.
Harsha K R