Yes, if you google for "lead screw" or "ball screw" you'll find all
types.
www.mcmaster.com stocks several
varieties too. But if your planning on using it in a wet environment I'm
not sure a lead screw is your best solution. I don't think it would
take much sand to jam up any lead screw. The ones I have seen are always
well lubricated and shielded when in unclean environments. I have
never seen one used submerged. They do allow you to finely position a
load, but being within 1/32" is not that important right? Someone
suggested chain, and that is what I plan to use too. The chain runs
a loop from the drive sprocket to an idler sprocket and back. I
purchased some used stainless steel roller chain of eBay for a song. But
instead of relying only on the chain for the weight, you can use it to
move a lead weight. The down side is safety. If a lead screw drive
fails the weight is less likely to move, but if a chain breaks then both
the weight and the chain are going to head down hill. If anyone has
experience with using "lead screws" in ocean like environments it would
be helpful to hear your thoughts.