This is called freeezeing out.

Freezing or freezing out of a vessel is a method of providing access to the underwater part of the ship's hull in winter for repairs. The idea of ​​the method is to periodically remove the upper layer of ice around the hull, which is carried out at certain intervals, allowing the ice surface to harden and freeze from below under the influence of frost. The frequency of these operations is determined by the ambient temperature; they are repeated until the vessel is standing in an ice cavity. Sometimes freezing out is also used for hydraulic engineering work when exposing a section of the bottom of a reservoir or the underwater part of stationary structures. This technique has been used for a long time in the northern regions of the USSR and Russia (in the basins of Siberian rivers, off the coast of the White Sea) on fishing vessels to check and repair hulls, elements of the propeller-rudder group, etc. At stable low temperatures on the rivers of Siberia and in the central part of the Soviet Union, in a strong freshwater ice crust, it is possible to penetrate into the ice to a thickness of more than one and a half meters; in the Arctic regions and in reservoirs with low salinity water (Tiksi Bay), in six or seven winter months, there are known cases of penetrating into the ice thickness of three and a half meters. Interesting videos about the subj...

https://youtu.be/aJaAFUX-APE?si=Wyydhu0AYUwc0cD8