If I reduce the speed of a vessel, then the propeller will make less noise because there's less energy introduced to the system, so less is lost as sound.

• Marine dB doubles each decade
• After 9/11, shipping stopped and whale stress hormones went down 40%
• Hearing loss/tissue damage
• Mammals run from noise, disrupt feeding and migration
• Can’t hear each other
• Noise ups stress, lowering immune functions
• Makes it harder for whales to tell if a boat is near
• There are on average 95 dB of noise in the communication range of 1-5 kHz for whales
• On average, 3 dB quieter per knot of speed loss
• Being close to a boat can make it very hard to echolocate 
• Can hit boat and get hurt by propellers
• Oysters are struggling to find a good home
• Oysters close up when shipping vibrations are felt

• Manipulated Variable
  • Throttle setting of the boat
• Responding Variable
  • How loud the boat is in dB
• Controlled Variables
  • Which microphone was used 
  • Size and design of the boat
  • Temperature of the water
  • Turbidity of the water
  • Amount of water

1. Assemble the boat
2. Connect and insert electronics
3. Test dB meter
4. Fill bathtub with water until boat can move freely anywhere in the water
5. Set motor speed to 30%
6. Check dB meter and record reading
7. Set motor speed to 60%
8. Check dB meter and record reading
9. Set motor speed to 100%
10. Check dB meter and record reading
11. Repeat steps 5-10 five more times

Overall, noise increased with speed, with a maximum dB count of 82, and a minimum count of 65. The total difference between high speed and low speed was 17 dB, with a total increase of 16%. A roughly linear increase was shown, with a slightly more rapid increase at the lower end of the graph.

The data from the experiments showed that slowing the boat decreased how loud the boat was. However, doing this comes with tradeoffs. You can’t get to your destination as fast, and that can be very annoying if you have a time to be somewhere. Even though it was much quieter to move at a lower speed, most boats aren’t very efficient at low speeds and aren’t quite as stable. My hypothesis was correct, although there is nothing to show that the reasoning behind it was the real reason it was correct.

There are lots of ways to try and mitigate aquatic noise and its impacts on marine life. One way is to slow down, as on average, 3 dB of noise are mitigated per knot that a ship slows down. Another way is to use quieter engines that vibrate less. Electric motors have low vibrations compared to gasoline or diesel engines. Also, as a side benefit of electric boats, they are better for the environment than fossil fuels. Lastly, to mitigate noise we can get rid of propellers and moving parts entirely. I made a small demonstration MHD thruster, which has zero moving parts or noise. It is also 100% electric. Another way to get rid of noise is to go back in time and use sailing ships.

• Power variations slowing or speeding up the motor
• Background noise interfering with microphone
• dB meter inaccuracies
• Imprecise manufacturing in parts
• Propeller design being different from that of a cargo ship

• earth.org 
• tethys.pnnl.gov 
• jpi-oceans.eu 
• arcticwwf.org 
• ncei.noaa.org 
• fisheries.noaa.org

Thank you to my science fair coordinator, Mr. Bykovskikh, who is one reason why I am here. Thank you to Ms. Beatty, who helped me figure out many small details in my project. Thanks to my family, especially my sister, Helen, who made me do all of the things I didn't want to do as much.