To make a decent solid reel is not that hard. Take an old lpg cylinder or similar cut off end domes, reverse and weld a piece of pipe the right diameter in the middle, ie use the domes to create nice curved ends for your reel. Place shaft through the middle of the reel, add a bearing each end. Make up a frame to carry and bingo! I think its better to direct drive rather than use belts or chain as less to catch fingers in.

Safety note-- make sure to remove the valve from end of any cylinder and wash out well! before taking a cutoff blade to it. Should be a no brainer but you never know.

Don’t really think a bilge pump motor would have an enough torque. But I would suggest finding a large windscreen wiper motor off a truck etc. These are normally reasonably waterproof, rated for continuous use and have heaps of torque. Or the motors off electric wheel chairs are perfect, but not that easy to find.