As a 'seaman' - you might qualify to be overweight or not pay for luggage. Check with your scheduler at the cruise line - you'll probably need to show your seamans book (if you have one) and/or letter of employment from the line when checking in. I don't have the book, but have used the 'LOE' and didn't have to pay for an extra bag once (can't remember the airline)
Also check and see if you can mail anything you don't need immediately to the ship directly - usually the same address any crew mail is sent to. I usually send ahead vitamins/hair care products when I'm based out of non-US ports. Mail goes to our Miami office and then is sent in bulk to the ship for turnaround days.
The mail thing is VERY popular for crew when signing off. Amazing how much crap you can accumulate in a contract! Mail home a suitcase instead of flying . . .