The vessels firm installed the 18th Siemens 6MW turbine at the site, located eight kilometres off the UK's east coast.
A total of 35 turbines will be installed by A2Sea's Sea Challenger vessel. It is the first commercial project to use Siemens' turbine.
Westermost Rough is due to be fully commissioned in the first half of 2015.
Seaway Heavy Lifting installed the project's substation in June 2014, and the first turbine was installed in August. Westermost Rough began producing power just three weeks later, at the start of September.
The project's developer, a consortium of Dong, Marubeni and the Green Investment Bank, was recently named in a patent infringement lawsuit between Siemens and Wobben Properties.
Wobben claims Siemens is using patented technology in its 3.6MW and 6MW turbines.