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.Read More