Removing Fishline From Props

Story And Photos By John Tiger

Fishing line can cause a world of damage to your engine.

Photo of outboard engine entanglement with a fishing line

We've all seen this. A fisherman gets his or her reel snarled with a tangle of fishing line, cuts it all off, throws it in the lake, and restrings the reel. Seems harmless enough, right? After all, that mess just sinks to the bottom, never to bother anyone.

Wrong. First, monofilament fishing line doesn't sink immediately. It actually floats just under the surface, and is almost impossible to see. Chances are very high it will "catch" on your outdrive as it passes through the water. If it doesn't get caught on your gearcase it can cause grave danger to aquatic life; fish, turtles, and seagulls often die from getting wrapped up in fishing-line snarls.

The Damage Done

When fishing line gets ensnared in your engine's gearcase, it can cause major damage, very quickly. Unfortunately, it's damage you won't even notice until your gearcase fails, or if you're lucky, when you're servicing the unit during a regular maintenance interval or at the end of the boating season. Here's what happens: the fishing line gets caught in your spinning prop, and quickly wraps itself around the prop. As it does, it slides into the narrow gap between the forward end of your propeller hub and the rearward edge of your gearcase. Once there, it gets wrapped around the propshaft just behind the forward thrust washer, winds and winds around the shaft, heats up — and melts. Often, it will melt into a brittle plastic disc, with sharp edges. As it melts, loose strands cut into the prop shaft seals that are located right behind the forward thrust washer. There are typically two propshaft seals, installed one behind the other. The inner seal is there to keep the gear-lubricating fluid in; the outer seal is there to keep the water from getting in. When the fishline cuts through the rubber lips on these seals, it's just a short matter of time; water seeps in, and gear lube seeps out.

Without frequent inspections, you'll never know until it's too late. After the water contaminates the lubricant, its ability to keep the gears and bearings lubricated and cool diminishes. Bearing and gear failure can result, but often it's the rust that forms as a result of the water intrusion that's the actual cause of failure. The key is vigilance and periodic maintenance. It costs about $30 or so to drain the gear case and refill it with fresh lube. It typically costs well over $2,500 to rebuild a gearcase with new gears, prop shaft, driveshaft, and seals.

Check Lube And Seals

While you might get lucky and spot lube dripping from the end of the gear case, usually the water washes it off before you have a chance to see it. Here's the best way to keep an eye on your gearcase's seals and the lube inside:

Photo of propeller thrust washer entangled with fishing lineThe strand of fishing line protruding out from behind the propeller thrust washer indicates that the line has wrapped around the propshaft, and will cause a seal leak if left uncorrected.

  1. At least once per season, remove the prop and thrust washer, and visually check for fishing line wrapped around the prop shaft. Remove all traces if you find any. You may have to cut it off with a sharp knife. Check the seals carefully with a magnifying glass to see if they've been cut or ruptured.
  2. Drain the lubricant from the gearcase, taking careful note of the appearance and smell of the gear lube. If it's a nice, clear color (uncontaminated lower unit lube is usually amber, blue, or red depending on brand and manufacturer), it's fine. If it has a milky, bubbly, coffee-colored look, it's contaminated by water, and the seals must be replaced. If it's a blackish color and has a burned smell, the gears and bearings may be overheating and on their way to failure.
  3. Usually, the lower drain screw has a built-in magnet. It's normal for this magnet to collect a small amount of very fine metal filings. This is from the gears wearing together. However, if the fluid is black and smells burnt, and the magnet is covered in larger metal shavings, the gearcase has an internal problem and should be serviced.
  4. Lastly, don't ever put your rig away for winter storage without draining the old lube and refilling with fresh. If you catch potential water intrusion before the off-season storage period, you may save the unit from rusting up as it sits through the winter. Any water inside will simply sit on the steel surfaces of the bearings, shafts, and gears — and cause rust that will lead quickly to failure. Even if you can't service the seals then, better to refill with fresh lube until you can.  

John Tiger's life has been spent in the marine industry. He owned his first outboard at age 7; since then he has owned more than 60 boats and outboards. He started outboard racing at 14 and is still active. See his story on vintage raceboats "Old Outboard Racers Never Die".

— Published: April/May 2015


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