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University of Minnesota researchers offer new water depth recommendations for powerboats, wakeboats to reduce harmful environmental effects.
Illustration of the three hydrodynamic phenomena produced by a powerboat and how they interact with the water column beneath the boat. Courtesy, University of Minnesota
Complaints about wake surfing mostly focus on the ripple effects caused by wakes (rocking boats, shoreline erosion), but a new study shines a dramatic light on the damage that slow passes over shallow water does to a lakebed and water quality.
“A Field Study of Recreational Powerboat Hydrodynamics and their Impacts on the Water Column and Lakebed” by research staff at the University of Minnesota’s St. Anthony Falls Laboratory identified three hydrodynamic phenomena produced by recreational powerboats that impact the water column and lakebed: bow and stern pressure waves, transverse waves, and propeller wash. These forces collectively stir up and suspend sediment, including phosphorous, a primary fuel for algae blooms, and can shear or uproot submerged aquatic vegetation.
Researchers used seven recreational powerboats to conduct testing: two deck boats with outboard engines, three bowriders with sterndrive engines, and two wakeboats with inboard engines. The boats were driven over bottom-mounted acoustic-based velocity sensors at four water depths (9, 14, 16, and 27 feet).
They were filmed both above and below the water using aerial drones and underwater video to highlight the hydrodynamic effect and its damaging impact, even hours after the boat had passed. You can watch the videos on St. Anthony Falls Laboratory’s YouTube channel.
While the study found traditional small powerboats traveling at semidisplacement (surf) speed (10- to 12 mph) churned lower density sediments up to 10 feet below, wakeboats in surf mode agitated sediments up to 20 feet down.
The study concludes with recommendations that traditional powerboats should operate in 10 feet of water or greater when planing, or in displacement mode, to minimize impacts on the lakebed – but wakeboats in semidisplacement mode (surfing) should operate in 20 feet or greater depth.
Click here to read the full study.