The subject, composition, and use of light are painterly, but that's true of many photos. What's unusual is the abstract distortion seen in reflections off the water's surface. Here's a detail from the photo.
Quite a few paintings come to mind in which this sort of abstraction appears. Here are two.
The boats in the photograph are lateen-rigged. They use a large triangular sail which is attached to a spar. The spar is a long wooden pole which is raised and lowered on the mast via ropes called halyards and pulleys called blocks. One side of the triangle is made fast to the spar. Its front corner is attached to the bow of the boat. This is called the tack. The sail's back corner is controlled by a line called a sheet. The sheet can be let out or pulled in as required to catch the wind and make headway. Depending on the direction of the wind with respect to the path of the boat, the wind either pushes the sail from behind or pulls it from front or side. The boats can't sail straight at the wind; they must be at an angle to it which is sufficient for the sail to provide lift in the same way an airplane wing provides lift.
The boats have an ancient Middle-Eastern design much like the dhow or felucca. Across the world's seas where boats of this type have been (and are still being) used, their design has varied greatly. All share the stubby mast and long yard seen in these examples. All sail with the yard canted at an angle, the forward corner attached to the bow and the aft one controlled by the sheet.
Lateen rigs commonly have no second yard (or boom). The lower edge of the sail is attached to lines at the corners and is otherwise free. This gives the boats better sailing efficiency than the more familiar Bermuda rigs which have the fore edge of the sail attached to the mast and the lower edge attached to a boom. Lateen rigs are simpler and a lot cheaper to build than the Bermuda ones. Despite large sail area, they have ample headroom in the cockpit and often have a roofed structure — an open cabin — in the aft part of the vessel. This shed-like structure is present in the boats shown in the photo. It serves a double purpose, both to protect occupants from sun and foul weather and to provide support for the long yard when it is lowered, as it is on the boat at left.
Boats of dhow or felucca design can be multi-masted and quite large. Sixteenth-century Portuguese navigators used lateen-rigged ships called caravels in exploring the coasts of Africa and the Indian Ocean and one of Columbus's ships, La Niña, was one of these caravela latina. Lateen-rigged ships were also favored by Mediterranean and Caribbean pirates.
This painting shows lateen-rigged ships of the eighteenth century. The two ships at either side are galiots sailed by Algerian pirates. The ship at center is a Spanish naval vessel, a xebec (here called a jabeque), which is fighting them off.
Large lateen-rig boats were superseded by steam vessels and the boats we see in San Juan harbor remained the most common general size from the late nineteenth century onward. These small craft lack the romantic association of armed corsairs and naval vessels, but have their own clean-lined grace and charm. Prosaic and work-a-day, they nonetheless marry function and form quite well and their proportions are pleasing.
In use, they are highly maneuverable, comfortable in harbor, and seaworthy in unprotected waters. They can be rowed or poled as well as sailed. They can carry passengers, merchandise for sale, or goods for transport. They can be used for fishing or as floating delivery wagons. Cheap to make, easy to maintain, and not difficult to sail, they are anything but rich men's toys.
Here are some detail views from the photograph.
The boat in this detail has a split yard. Segmented yards were required when sailors needed to stow the mast and yard within the boat, the yard being otherwise too long. Because in this case there is one long segment and one short one, it's likely the sailor has split his yard to make it easy to replace the longer section, which is a the branch of a tree, when it wears out or gets damaged.
Since the long lateen yards could be quite heavy, sailors used a pulley system -- halyards and blocks -- to raise and lower them on the mast.
Lateens came into use some two thousand years ago as an efficient alternative to square-rigged sails which run well before the wind but cannot effectively reach (when the wind is abeam) or tack (when the wind comes from a front quarter). Although they make more effective use of the wind than the more familiar Bermuda rig, they are not nearly so good at the maneuver called tacking. When a sailboat's course requires it to progress directly upwind, it is forced to sail in zig-zags, sailing a bit to the right of wind (starboard tack), then to left (port tack). Lateen rigs are not as good at tacking as Bermuda rigs.
In lateen sailing a proper tack requires the sailor to shift the spar from one side of the mast to the other. This can be done by bringing the spar down, moving it to the other side of the mast, and raising it again. It's simpler, however, to pull the sail around the bow during a jibe. The boat jibes when during a port or starboard tack, it moves away from the wind and comes back in a full circle. When half the circle has been completed and the wind is now behind the boat, a crew member passes the sheet around the bow and pulls the sail, and the spar with it onto the other side of the boat. Much of the time lateen sailors do not move the spar when tacking and the result is a "good" tack when the mast is windward of the sail and a "bad" one when the wind flattens the sail against the mast and thereby decreases its efficiency.
This Dhow is sailing on a "bad tack." The wind is coming from starboard (it is at the cameraman's back) and the sail cannot bellow out as fully as it should because the mast gets in the way.
This dhow has let the sheet go before jibing, and will let the sail whip like a flag as the yard is moved to the other side.
In gusty winds or heavy weather, sailors usually reduce sail area, that is shorten sail, by what they call reefing. Lateen sailors can do this, but they generally do not put reef points in their sails. Reef points are grommet holes which allow short lines to be used for reducing sail area by tying the sail down. In practice lateen sailors almost always rely on the flexibility of the yard (it is whippy), or they lower the yard on the mast, or hitch the sail near the top of the yard, or drop sail and row.
Here's the full image again, a bit sharper and with lowered gamma, to bring out detail.
Here are two photos of San Juan harbor taken at roughly the same time.
1. The first shows the harbor from landside.
2. The second shows the harbor from the end of the wharf.
This detail comes from the first of the two.
This detail comes from the second.
These drawings show the essentials of a lateen rig.
This two-minute YouTube video tells what little is known about the origin of lateen-rigged boats and shows them in use. In it you can see a number of "bad tacks." Because the mast presses against the sail in these tacks, they're easy to spot. It's apparent bad tacks are not as efficient as good ones but the difference is modest.
This drawing shows how wind propels a boat by means of lift.
Here are two models of large lateen-rigged ships. At left is a model of a 16th-century caravel, a caravela latina, such as the ones used by Portuguese navigators. At right is a model of a Spanish xebec or jabeque, a pirate ship of the Caribbean.
This image gives an idea of the efficiency of the lateen sail — its ability to provide greater lift than other sail shapes are able to do.
This image shows the use of the halyard and block to raise the yard on the mast. It also shows that a small lateen-rigged boat can easily be sailed by one person.
THE HISTORY AND CONSTRUCTION OF THE DHOW on Nabataea.net
Madagascar Dhows on the blog of the sailboat Marcy from Seattle, USA
Dictionary of American Naval Fighting Ships, Department of the Navy -- Naval History and Heritage Command, Washington Navy Yard, Washington DC 20374-5060.
Basic Sailing Rigs shapes on the DIY Wood Boat web site
Sailing rigs (masts and sails) on the Transition Rig web site
Thread: Lateen on woodenboat.com
Caravel on wikipedia
Tack (sailing) on wikipedia
Lateen on wikipedia
Forces on sails on wikipedia
Bermuda rig on wikipedia
Felucca on wikipedia