A two images ago I did a shot of the river and this boat could be clearly seen docked but sticking out into the river.
Now I know why: it was to be hauled out for inspection and here is a video of that haul out.

Here is the description of the boat from the person who took the video: "The vessel is 85 feet long, 24 feet wide and about 150,000 pounds. The owner hauls the vessel out during the winter for the inspection onto a icy mound of snow. Later, cribbing will be added underneath to support the boat. Once the snow melts, the bottom will be accessible for the C.G. Inspectors to check hull plate thickness and for any damaged underwater structure. After the final inspection, repainting and other maintenance the vessel will be re-launched using bananas instead of grease on the slipways."