Honda Motor Co of Japan filed a U.S. patent application for a propeller guard partially consisting of an air bag
The patent application, US 2023/0278686 A1 “Outboard Motor Control Apparatus and Control Method for Outboard Motor” was published by the U.S. Patent and Trademark Office on September 7, 2023.

Honda’s patent application has to do with preventing propeller contact with objects or people behind the vessel. It also focuses on preventing objects from winding up on the propeller. This post will focus on Honda’s efforts to prevent people from being stuck by a propeller while behind a boat.

An image of the device is shown below:

Honda air bag propeller guard patent drawing

The device consists of a soft, elastic rearward protrusion from the propeller containing an airbag.

How Honda’s Airbag Propeller Guard Works

First, please note Honda does not refer to this invention as a propeller guard. They call it an “Outboard Motor Control Apparatus and Control Method for Outboard Motor”.

If someone contacts the soft, elastic protrusion behind the propeller, it mitigates their impact. Then the resistance to rotation begins to slow the rotational speed of the propeller. Or, it begins to slow the acceleration of the rotational speed of the propeller. Thresholds are determined and programed into the Engine Control Unit (ECU). This slowing or rate of slowing can also be used to determine if it is a person or not. The system can affirm a person is there via infrared sensors or a camera.

An alarm can be sounded depending on what is in contact with the protrusion behind the propeller.

If it is a human, priority can be assigned to this finding. Propeller rotation can be quickly stopped and an air bag can be inflated to push the human away from the propeller.

The air bag can also slow the human down if they were rapidly approaching the propeller.

The Diagram below shows how the system basically works.
Note the power system is referred to as “the prime mover” leaving room to cover fossil fuel engines, battery powered outboards, or other prime movers.

Honda air bag propeller guard diagram patent drawing

The Logic System

The basic logic used by the ECU to make decisions surrounding this propeller guard or virtual propeller guard is shown below.

Honda air bag propeller guard logic map patent drawing

Other Features

The patent application speaks of urgently stopping the rotation of the propeller. However it does not elaborate on how that will be done.

The soft, elastic protrusion containing the airbag can be detached from the propeller. This makes it easily installable for specific applications. No specific applications are listed. Some potential outboard powered boat applications that come to mind are:

• skiing and tubing
• rental houseboats
• rental pontoon boats
• dive boats
• boats used in “raft ups”
• youth sailing coach boats
• rescue boats and flood rescue boats
• Some might suggest their use on outboard motor powered boats during wake surfing. That is a debate for another time
• military applications
• protecting commercial diver airlines from the propeller
• military minesweeper arrays on the surface of the water, towed by helicopters use very expensive cables that might be protected by this device

Even More Features

Honda’s patent application describes an emergency button on the outboard motor at a location that could be triggered by swimmers that feel they are in danger.

Most outboard motors are used with through prop exhaust. This patent application does not explain the details of that feature.
There may be additional patent applications coming with greater details on certain elements of this invention.

Automotive airbags and refilling them can be very expensive. Many boaters are used to more economical cartridges used to inflate life jackets. No mention is made of the cost of Honda’s approach.

The system is adaptable to boats powered by multiple outboard motors.

Mechanics of Filing This Patent Application

Honda Motor first filed a patent application in Japan on December 28, 2021.

Almost a year later, they filed the U.S. patent application on December 13, 2022.

The U.S. Patent Application was published September 7, 2023.

Our Comments

We salute Honda Motor for thinking outside of the box and placing one more approach to boat propeller safety in the literature.

We hope Honda is able to bring this device to market and generate more interest in this field.