So what is going on here? The Polar Star suffered a rather difficult season in Antarctica in 2017-18--two of three propeller shaft seals failed, and one of the three 25,000 hp gas turbine engine generators failed as well. These difficulties are described in this February 2018 Coast Guard News article which includes a link to photos from the 2017-18 Deep Freeze deployment. In April, the icebreaker entered a dry dock at Mare Island Dry Dock LLC (the current name of the private facility that took over operation of the former Mare Island Naval Shipyard after it was decommissioned in April 1996). Here's a YouTube video from KPIX Channel 5 from the media day which was held shortly after the icebreaker's arrival.
Not the Polar Star's first time in this shipyard...it's spent time here for major repairs several times in recent years. This year's yard period is expected to last 5 months and cost at least $5.9 million dollars. Here's a mid-June video report, also from KPIX.
Below, a series of mid-June photos featuring one of the replacement propellers. These are from the U.S. Coast Guard Pacific Area's Facebook page.
Down inside the dry dock, preparing to rig up on one of the new propeller screws.
A closer look at one of the new propellers.