I wrote about this some years ago, so it is not a completely new subject. However, I continue to see people and marine companies use an incorrect word to refer to the marine bearing that cradles the propeller shaft as it exits the hull.

To be clear, it is called a “cutless bearing,” not a “cutlass bearing.”

Most direct drive boats have one or two of these bearings, although in recent years we’ve seen the introduction of new thrust and marine bearing systems, such as those offered by Seatorque Control Systems, which are standard equipment on the Northwest Yachts 63 and larger expedition trawlers. The company’s BOSS system is an enclosed, oil-filled shaft and thrust bearing assembly that is a complete unit from transmission to propeller. As the propeller shaft rotates within an outer shaft casing, there is no need for a separate and standalone cutless bearing to cradle the prop shaft. (I hope to get an opportunity to examine this system in the future.)

In any case, noting the confusion regarding the spelling of the traditional approach to marine bearings, several years ago I reached out to professionals in the marine industry that I knew. Unfortunately, no one could agree on the correct spelling of the bearing, one way or the other.

boat propeller cutless bearing

But I eventually found the true history and origin of the term. And its roots are not even nautical.

I called Dave Gerr, author of The Propeller Book, and at the time head of the Westlawn School of Yacht Design. He also didn’t know, but suggested I called Mike Schonauer, who was then VP of Sales & Marketing for Duramax Marine in Hiram, Ohio. Duramax is a pioneer in marine bearings.

Mike was happy to explain the history of the bearing, in which his company is a part. In the 1920s, Charles Sherwood was an engineer responsible for maintaining vertical lift water pumps used in mining operations. The traditional bearing material used in these pumps was lignum vitae, the world’s heaviest and densest hardwood. Given the abrasive nature of this water, sludge, and mud pump application, the hardwood bearings needed frequent replacement, a regular chore for Mr. Sherwood.

Preparing to again replace a pump’s bearings, he found they were out of lignum vitae. A clever engineer, he searched his shop for alternatives and found a sheet of rubber. Having nothing to lose, he decided to cut some temporary bearing strips for the pump from the rubber material, getting the pump back online. He kept an eye on the pump’s operation over the next several weeks while he restocked his hardwood supply.

He was intrigued to find the pump shaft was doing nicely with the rubber bearings, much more so than with lignum vitae bearings. He noticed the shaft was not being grooved or worn by the rubber bearing, even in such an abrasive environment. The rubber bearing had, in fact, “cut less” into the shaft surface than the hardwood bearings. Dirt and other particles would push into the rubber strips and roll across them as the shaft turned, flushing away once it reached the open channels separating the strips. The rubber was the key to minimizing pressure between two hard surfaces to score the shaft.

A year or two later, the bearing was patented by Charles Sherwood in conjunction with Lucian Q. Moffit of Akron, Ohio, who coined the term “cutless” bearing.

Mr. Moffit eventually sold out to B.F. Goodrich, where in the 1950s, the bearing division came up with the marketing idea of stamping a sword symbol on its cutless bearing products as a form of branding. The confusion was born of the cutless bearing with the symbol of a cutlass.

Johnson Rubber, also started in the 1920s, in which Duramax Marine was a division, made its own version of bearings and stuffing boxes. Duramax Marine became its own corporate entity in later years, and eventually purchased the bearing division from B.F. Goodrich.

Today Duramax Marine makes all sorts of bearings, cutless bearings included, for hydroelectric turbines, agricultural vertical pumps, and many other applications outside of strictly marine use. The design of the cutless bearing allows it to handle much greater loads than roller bearings, due to the lubrication features of the bearing design.

And to further distinguish the bewilderment between a cutless bearing and the cutlass sword, Mike Schonauer offers that today the proper term for the bearing is a “water lubricated, hydrodynamic standard rubber sleeve bearing.”