In looking through the book "The Triumph of Unarmed Forces" On 1 march 1917 it mentions the Merchant ships Gurre sunk and Livingstone taken as a prize by a U-boat in looking at this site it was the U66. This book also mentions on this same day right after sinking the Gurre the same U-boat was driven off by gunfire by a British merchant ship BVLAS mentions the Birchgrove doing this in the North Sea on this date so it might be the ship. the Birchgrove was sunk by the U84 on 2 December 1917 according to this site.
This book also mentions to same U-boat stopping and letting go to Denmark to Danish Merchant ship Holthe which had a cargo of oilcake.

I hope this of some use or interest.