If you want to get to the mainland from the Cowes area, Red Funnel are your main option.  They have two services to Southampton.  The car ferry operates from East Cowes while a fast catamaran provides a passenger only service from West Cowes.  Both types of ferry came by while I was on the seafront.  The car ferry headed out while the cat waited outside the harbor.  I guess the strong winds meant they were looking for a bit more space.  Once the ferry was gone, the cat came in to the harbor.