Possible Clues:

• Chap after dieting who's often seen in dock?
• Fellow on boat less serious having got to isle
• Dock worker's less serious fellow
• Stevedore who doesn't carry as much weight as others?
• Perhaps match island's help for loading ships
• Bargee less likely to win a straight fight?
• One at the docks who has lost weight?
• Successful slimmer working on a flat bottom
• Docker after dieting?
• Crew employed by comparatively underweight bargee