More info on the vessel can be found here:
https://balticworkboatsus.com/vessel/pilot-1700-wp/
It has been shown that a majority (51%) of pilot ladders is secured by means of D-shackles, when secured at intermediate length. Previous research (Evans, 2020) has proven that this method has only about 50% of the strength of the pilot ladder when secured at full length (“double ended ladder”), or by means of the “endless-sling” method.