Possible Clues:

• Kept without having to pay over the waterline (9)
• Accommodation costing nothing? If it disappears, one may be sunk!
• Nothing to pay to keep one up above the water
• Paying nothing for meals in upper part of ship
• You don't have to pay for your keep on there over the water
• Nothing to pay for what you eat up over the water?
• Nothing to pay so to be kept above the surface
• Nothing to pay to keep you above water
• That will keep one above the waterline and off the breadline, it seems