Above are a couple of pictures of what are known as an Aqua Marine Supply (AMS) Enclosed Belt Drive 'EBD' Hoists.  The upper picture depicts a wired package that's available at Boat Lift Warehouse.com.  The 3000 lbs unit with 3/4 HP motor retails for somewhere over $500.00.  The 4000 lbs unit with 1 HP motor retails for $545.00  These units are reportedly a bit faster that the typical flat plate hoist, with advertised travel speeds of 4 - 4.8 ft. per minute. Note: speeds are always dependant upon take-up drum diameter - amount of wraps on the drum and the actual diameter of the wire rope used.

As you can see from the lower of the two pictures, the output shaft is just peeking out from above the belt at the 6 o'clock position.  They claim that this unit never needs greasing.
Well, there's no longer a need to try and visualize what a boat hoist drive attached to a crank-up tower might look like.  As of May 2011, Dave Banner - N7BAN with the help of metal crafter extraordinaire  Christian Perri - KF7P of KF7P Metalwerks have a working example of one of the EBD drives that's depicted above, up and running.  See the whole series of N7BAN's pictures at 
http://bannerfamily.net/gallery2/main.php?g2_itemId=959  Email notes on construction from N7BAN here.