Icebreakers

[ombugge]

@texastanker

variable pitch props

Controllable Pitch Propellers (CPP) has been around since the mid-1930s:

1935

A.M.Liaaen (later acquired by Ulstein) develops the first controllable pitch propeller.
A.M.Liaaen patented their CPP for large ships in the US in 1972.
A.M.Liaaen CPPs were supplied to several US Navy and USCG vessels.

Maybe the Polar Star was one of the USCG vessels being equipped with A.M.Liaaen CPPs?

Source: Controllable Pitch Propellers (CPP)