Deployable Propeller Guard

As part of my senior capstone project in Fall 2025, I worked on creating DORI, a deployable propeller guard intended for outboard boat engines. The product was designed as a preventative measure that could be deployed when the operator of the boat entered a high risk situation such as an overturned boat with swimmers in the water. One of the largest markets this product was designed for was youth sailing instructors. Propeller related injuries have become a growing problem in youth sailing, and existing solutions receive serious pushback since they impact the maneuverability and fuel efficiency of the boat. This was a bit of a passion project for me since I worked as a sailing instructor for two years, and I have experienced both the problem and the need for a better solution.

Final Presentation

The class concludes in a live product launch where each team goes on stage with an 7-10 minute presentation including a live demo and a Q&A. I was one of my team's presenters, and you can see our presentation if you skip to 2:05:30 on the livestream.

CFD

I ran CFD simulations to approximate the drag forces on one of our guard prototypes. Simulations were run at 2m/s, 4m/s, and 10m/s yielding drag forces of 65N, 258N, and 1616N respectively.

My teammates then ran tow tank tests with a similar guard prototype to verify my CFD results. They ran tests at 0.3m/s intervals up until 1.8m/s then fit a curve to the data to try to predict the drag forces at higher velocities. Their model predicted drag forces of 395N at 5m/s and 1580N at 10m/s. On the left is the model generated by my teammates. Note: the graph depicts force in pounds.

Sensing

Our inital concept was a system that would sense when a person fell off the boat and deploy a propeller guard before the person made contact with the propeller. For the sensing component of this system, we looked into a variety of methods including wearables, lidar, and sonar. We ultimately decided on sonar, and used a BlueRobotics Ping Sonar Altimeter and Echosounder for testing. We first tested the sonar's ability to detect a person jumping into a pool, and then took to the river to try and integrate it with an outboard engine.

We decided to mount the sensor to the lower unit of the engine. This decision was made to minimize the added drag of the sensor. One concern we had with this mounting system was that as the boat was turning, it would point outside the path of the boat. Note: a line was affixed to the sensor and above the cavitation plate to further constrain the sensor in the y-direction.

We created a model of a small child by sewing rubber plates into a rectangle with roughly the same frontal area of an 8 year old. Rubber was chosen as the material because it has a relatively similar density to the human body and it would not damage the propeller if struck. The model was tied to a buoy so that it would rest in the water with the top edge near shoulder height of a child treading water. We were unable to reliably sense an object in front of the propeller using only one sonar, and adding an additional sonar would make our product far too expensive for our users. Given the limited time in the class we decided to pivot from automatic deployment and sensing to manual deployment.

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