Prop Shaft Line Cutters

A line or weed tangled in our pop can ruin your whole day, if not end your cruise. Here’s the remedy.  (published April 2015)

Every year we hear of boats that are abandoned at sea or along the coast because they have lines or sheets tangled in their props and are unable to motor to safety. On sailboats, when the rig comes down, a fouled prop is the next likely thing to happen in the now cascading series of emergencies. Yet, even with the rig over the side, you ought to be able to motor home, you ought to be able to use your engine without getting lines tangled.

And, if you are headed into high latitudes where you often find heavy weed floating in the sea, you can’t afford to lose your engine since it is what will get you home when all else fails. And, if you are headed into the waters of the developing countries, where trash and debris are often a problem in harbors and rivers, the chance of getting a length of line or debris snagged in your prop increases dramatically.

The solution is to fit your prop shaft with a cutter that is designed to slice through a piece of line, a jib sheet, a piece of polypro netting or even a heavy length of seaweed.

There are four popular brands of line cutters on the market, one of which needs to have the boat out of the water for installation and three that can be installed on your shaft by a diver.

The simplest cutter out there is the Shaft Shark sold by AB Marine. This little disc is made of 316 stainless steel and has an extremely sharp serrated blade that will saw through even the gnarliest ropes. Available in a range of sizes, the Shaft Shark is designed to stand proud of the diameter of your prop’s hub so it will carve up anything that comes its way. Yet, it also presents a very small surface to the water so it induces almost no drag while sailing.

The Shaft Shark comes as two semicircles that fit tightly together around the prop shaft. This design means that you can attach the cutter to your prop while the boat is in the water. You may need to hire a diver to do this but it will be much cheaper than hauling the boat out at a boatyard.

Evolution    Similar in design to the Shaft Shark, the Shaft Razor is also a two piece serrated line cutter that can be installed by a diver while your boat is in the water. The Shaft Razor’s significant difference is the second set of serrated blades that double the cutting surfaces and should help to slice effectively through heavy lines, weeds or debris. The Razor is also made of 316 stainless steel.

The Prop Protector is another dead simple line cutter that can be installed on your shaft by a diver while the boat is in the water. British designed and manufactured, this cutter has a straight cutting edge that is honed to a razor finish and will cut quickly through anything it comes in contact with. Unlike the serrated blade cutters, the protector can be removed from the shaft and sharpened, which means it will give many years of reliable service. More than 20,000 Prop Protectors have been installed worldwide.

Spurs Marine has been manufacturing and selling their eponymous line cutter for many years. A more complicated cutter, the Spurs device uses a scissors action driven by the force of the turning prop shaft to cut through rope, weeds and debris. Designed for all sizes of yachts and large vessels, the cutters are built with hardened 316 stainless and sharpened to a razor edge.
The Spurs unit comes as two parts so you don’t have to pull the prop shaft to install one on your boat. But, because the installation is a bit more complicated than the disc cutters above, you will need to install your new cutter during the annual haul out or the next time you need to apply antifouling paint. Spurs will recondition and sharpen your cutter in their factory thus extending its lifespan indefinitely.

Volvo Marine offers a Volvo line cutter that is designed to work with Volvo engines and props. The cutters have serrated edges and come as two-part units that can be installed by a diver.

If you are sailing where there are lots of crab and lobster pots, coastal fish weirs and netting, concentrations of weed or lots of flotsam and jetsam—just about everywhere—then adding a line cutter to your prop is like adding real insurance. One day the cutter can make the difference between a minor incident and a cruise-ending accident.

Author: Blue Water Sailing