Following on from Mike Yates's note:
I took a quick troll through the Roud Index for this song - Roud 690, and found
several different names for the said Captain.
From Hampshire, via Dr. Gardiner, there are versions By James Blooming and Richard Hall where he is called "Summerswell".
From the Collinson Manuscript we have a "Summersville", and also Collinson has the Copper family version were he suggests the name is "Daffodill" !!!

Take your pick which it was. By the way, there was also a Somerville mentioned who was under Nelson's command.

Tim Radford