Beam Reach

Testing the Thrustor for noise mitigation potential

Yesterday Marla Holt and I teamed up to measure the source levels (broadband and spectrum) of a new device called the Thrustor. Essentially a cowling that houses the propeller, the Thrustor is known to increase the efficiency and “bollard-pull” power of an outboard or stern-drive engine propulsion system. The Thrustor was co-patented by Terry Smith in 2005 and is manufactured by Marine Propulsion Technologies.

Terry drove his test boat up from California, his brother Chris flew out from Colorado to lend a hand, and Leif Bentzen provided and captained a boat from which to deploy the hydrophones. Marla and the Northwest Fisheries Science Center donated her expertise, her calibrated Resond hydrophone system, laser range finder, and hand-held GPS. I brought along the Beam Reach calibrated Inter-Oceans system and some buoys to mark the 100m and 400m ranges from the hydrophones. And thankfully, the weather really cooperated — while we expected drizzle and wind, we got clear skies and placid waters.

Despite substantial background noise from the Edmonds-Kingston ferry and passing freight trains, we gathered a bunch of data using dual-hydrophones that have a flat frequency response from 1-40kHz and are capable of recording up to frequencies up to 96kHz. First we tested Terry’s boat (powered by a Honda 80hp outboard) without the Thrustor, then with it. We made passes at 7-30 knots at ranges of 400, 100, and ~50m. We also measured the noise generated when accelerating from an idle to cruising speed.

Stay tuned for some preliminary acoustic results… For now, here are some photos from the day.

Why are our new ferries so noisy?

Thanks to Fred Felleman for the appended articles: new B.C. ferries are drawing complaints about being too noisy in air. One has to wonder whether the Coastal Celebration and its two sister ships, the Coastal Inspiration and the Coastal Renaissance, are also noisier underwater than their predecessors. The Celebration

BC’s Noisy New German Ferries

BC’s German Ferries May Be Lemons

BC Ferries Battles Fuel Costs

As killer whale scientists and conservationists we need to be more watchful of the ferry replacement process, particularly the standards for underwater broadband source levels and spectrum levels. We should all consider influencing the ferry selection/design process — on both sides of the border. For future replacements, let’s ensure that reliable estimates of noise impacts are available for existing designs and that strong underwater noise standards are required for new designs.

While the team who has selected designs for the new Washington ferries is confident that the new 144-car ferry will be more quiet than the fleet average, their modeling effort suggests there may be no improvement. The smaller ferry design is in operation on the east coast, but its underwater signature remains unmeasured.

More specifics at the Beam Reach wiki on ship quieting technologies