Propeller Guard Information Center

Marine drive companies have long employed damping / cushioning technologies to protect marine drives, most typically trim cylinder log strike systems that allow the drive to swing back, up, and over underwater obstacles. Recent years have brought several through hull drives to the market, most prominently Volvo Penta’s IPS, and Brunswick’s / Cummins Mercruiser Diesel (CMD) Zeus Pod Drive.

These thru hull drives, typically used on larger boats, are no longer able to be protected by the trim cylinder log strike systems because the drives do not trim. Volvo Penta and Mercury Marine / Brunswick have been issued several patents for break away drives and other techniques to protect the drive and especially to prevent the boat from sinking if the drive strikes a major obstacle, like a large rock.

In November 2011, Brunswick was issued U.S. Patent 8,062,082 for a “Marine Drive With Staged Energy Absorption Capability”. Targeting through hull drives, the patent describes a drive with a long, crushable nose cone. Depending on the amount of energy to be expended when a drive strikes an obstacle (speed of boat and mass of the boat), the nose cone can crush to absorb the energy, or the drive can “breakaway” from the boat. At lower energies (lighter boats and slower speeds) the nose cone crushes to absorb the energy, slow the boat, protect the main part of the drive, and prevent the boat from stopping so fast that people would be ejected. At higher energies (heavier boats and faster speeds), the drive breaks away in a manner that maintains the integrity of the hull and prevents water from entering the boat. The patent includes several charts showing the deceleration capabilities of varies designs. Brunswick introduces the idea of not only crushing the nosecone to absorb the energy, but also of allowing water to fill the nosecone, then forcing it out through one or more orifices during a collision, of filling the cone with an impact absorbing structure, filling the nosecone with an energy absorbing foam, and review previous approaches by others.

The industry is identifying technologies that can protect the boat, and the drive, and do so in a way that does not cause sufficient rapid deceleration to eject people from the boat.

Some of the earlier technologies, and the some of the more recent developments appear to hold significant promise for being able to reduce the impact / blunt trauma felt by humans when struck by a propeller guard. Anything that can reduce the rapid acceleration felt by humans when struck by a marine drive or guard AND the duration of that acceleration is a candidate for reducing injuries and their severity.

We anticipate publishing a post on the science behind blunt trauma injuries in the future which should also be a helpful reference to those pursuing this project. For those not familiar with blunt trauma injuries or who just think of them resulting from being whacked or hit with something, blunt trauma injuries result from sudden accelerations or sudden decelerations. Our organs, tissues, and even bones are damaged when they are accelerated or decelerated too quickly. Blunt trauma injuries can be reduced by reducing the peak accelerations and decelerations of humans struck by propeller guards.

We propose students consider Cushioned Propeller Guard design projects for their Senior Design Projects, Sr. Thesis, and Capstone projects to better protect humans and marine life from being struck by a propeller guard, and provide further information below. Read More→