[fatlazyless]

This suggestion does probably not apply to a marina with a lot of docks to protect but to a homeowner with the typical 6' x 30' dock, or so.

Instead of using a single 1/2 or 3/4-hp propeller water circulator, you can use 2-3-or 4 one/sixth horsepower utility pumps that cost about one hundred dollars, each.

Hung by a single line from under the dock, directly close to the dock support legs, it sucks up water from below and shoots it straight up, making a circle of active ripples that keeps the water from freezing into ice.

It spreads the energy impact on the water from one big propeller moving the water, to 2-3-4 smaller circles of ripple water and changes the dynamics of the water energy flow by keeping it closer to the dock supports legs ...... so's the open water doesn't get bigger and impact the neighbor's waterfront. It keeps it local.