Marine News from the Great Lakes

Wrapped Up: Fishline Snarls and the Damage They Cause

Published: Saturday, July 25, 2020
By: John Tiger

We’ve all seen this… an angler gets his reel snarled with a tangle of fishing line. He cuts it all off, throws it in the lake, and re-strings his reel. Seems harmless enough, right? After all, that mess just sinks to the bottom, and never bothers anyone.

Wrong. First, monofilament fishing line doesn’t sink; at least not right away, anyway. It actually floats just under the surface, and it’s almost impossible to see. Not that you’d see it anyway; you’re driving over it, and 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 and does cause grave danger to aquatic life; fish, turtles, and seagulls often die due to getting wrapped up in fishing line snarls.

The Damage Done

When it gets ensnared in your engine’s gearcase, it can cause major damage—very quickly. Unfortunately, this is damage you won’t even notice until your gearcase fails, or if you’re lucky, you might catch it 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 propeller 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 it slides into there, it gets wrapped around the propshaft just behind the forward thrust washer (the one between the gearcase and propeller). As it winds and winds around the shaft, it heats up—and melts. Often, it will melt into a brittle plastic disc, with sharp edges. As it melts, loose strands cut into the propshaft 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 fishing line cuts through the rubber lips on these seals, it’s just a short matter of time; water seeps in, and gear lube seeps out.

Trouble is, 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 on the steel surfaces of the gears, shafts, and bearings as a result of the water intrusion that is the actual cause of failure. The key is vigilance and periodic maintenance. It costs about $30 or so to drain the gearcase and refill with fresh lube. It typically costs well over $2500 to rebuild a gearcase with new gears, propshaft, driveshaft, and seals.

How to Check Your Gear Lube and Seals

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

  • At least once per season, remove the propeller and thrust washer, and visually check for fishing line wrapped around the propshaft. Remove all traces of it 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.
  • Then, 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 in color depending on the 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.
    >> Read “Do It Yourself: Gearcase Maintenance” <<
  • 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.
  • 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.


This article first appeared in the Summer Issue (Jul/Aug) 2020 of
Great Lakes Scuttlebutt magazine.

tags: Do It Yourself (DIY), Engines, Service & Repair

Go back | Show other stories

Check the Map!

Boat shows, destinations, magazine locations

Check it out!