How to Order a Propeller Shaft Line Cutter

Propeller shaft line cutters are an excellent way to help protect your boat from entanglement in marine debris. These devices are designed to help cut through rope, fishing line, netting, and even seaweed. While they don’t cut through everything, they’re effective across a wide range of marine debris.

Are Line Cutter’s Necessary

Line cutters are important to boaters because they help prevent damage to a boat’s propeller shaft and running gear system.  Light rope and monofilament can wreak havoc on a boat’s shaft bearings and restrict cooling around dripless shaft seals. Debris can also foul the propeller and/or rudder making it impossible for you to maintain headway.

The more sea miles you rack up, the more likely you’re going to experience entanglement in marine debris. Commercial mariners and avid cruisers both recognize a line cutting system as essential equipment.

Different Types of Line Cutters

There are two main types of line cutters, the first is the “disc” style and the other is the “scissor” style.

Disc Style:

As the name suggests, the disc style is a sharp symmetrical disc that mounts on the shaft just forward of the propeller hub. Sometimes the edge has serrated teeth, and sometimes they feature a circular razor edge.

Scissor Style:

The other style is a “scissor” system that has one blade rigidly fixed to a strut or bearing housing, while the other blade spins on the shaft. As debris meets the spinning blade it is turned into the fixed blade where the scissor action cuts it free.

What’s the Best Line Cutter

There are advantages and disadvantages to both styles of line cutters. While the scissor style offers a more active cut, they are more difficult to install and easier to damage. The disc style is more resilient to damage but requires a greater strain to be applied to the debris before it is cut free.

After years of research and testing, R.E. Thomas Marine Hardware developed the Piranha Dual Line Cutters. With a split design that’s easy to install, the dual serrated teeth offer an ideal cutting edge against marine debris.

The dual blade also offers redundancy against a single point failure associated with scissor systems. It’s no wonder why they were selected by the Canadian Coast Guard for their newest fleet of SAR vessels.

How to Determine Line Cutter Size

When ordering a Piranha Line Cutter there are four things you need to determine.

Shaft Diameter: Piranha Line Cutters are precision machined to clamp securely to a specified shaft diameter. You would not believe how many people think they have a 1 ¼” shaft when in reality they have a 30mm shaft (or vice versa).

Prop Hub Diameter: Prop hub diameter is import, especially larger propeller shafts. You want to make sure the Piranha’s teeth extend past the propeller, but not so much that they create drag.   

Prop Overhand Space: You need to make sure you have enough space between your shaft bearing housing and your propeller hub. You’ll need a gap equal to at least half the diameter of the propeller shaft to ensure adequate water flow across the shaft cutless bearing.

Exposed Taper: The final item to check when ordering a Piranha Dual Line Cutter is whether you have any shaft taper exposed. If the propeller shaft begins to taper before you get to the propeller hub it will be hard for the Piranha to secure to the propeller shaft.