On 25 May 1917 Thalatta was sold to Wynfield Shipping Co of Grimsby. A 70 hp two-cycle vertical oil engine was fitted in the former skipper’s cabin aft, built by Plenty & Sons of Newbury. She was used as a supply vessel to the Humber boom defences, with Percy Richmond as her skipper (who had previously been mate). Her fore-hold was converted to accommodate her crew which now included an engineer. Her rig was cut down and she worked from Grimsby as a motor barge.