A rowlock is a fitting on a boat which is designed to hold an oar while it is in use. These fittings are also known as oarlocks in some regions of the world. Most boats powered by rowing have rowlocks, which may be fixed in position or movable, depending on the type of craft and the design. A number of functions are served by a rowlock, and as ancient examples of boats can attest, these fittings have been around for a long time.
One obvious function of the rowlock is as a fitting to hold an oar in place while someone is rowing. Without a lock, the row or oar could slip out of someone's grip or skitter across the side of the boat when someone exerts force against it. The rowlock swivels, allowing for rotational movement so that the motion of the oar is not impeded by the rowlock. The rower can take the oar through a full range of motion without being stopped by the rowlock, in other words.
Rowlocks also act as a form of fulcrum. Fulcrums facilitate the transfer force, which in this case is created by the movement of the row. With the fulcrum and lever system created by the oar and rowlock, people can do more work with less force, relying on the fulcrum to transfer the mechanical work they put into an activity. Rowlocks make it easier to row, and make sure that each stroke of the oars counts, propelling the boat.
The most basic rowlock is simply a U-shaped attachment mounted in a swivel. People slip the oar into the U, and row normally. Some have a latching piece which goes across the U so that the oars will not pop out. Popping an oar can be extremely inconvenient and it can seriously hinder someone in a race, making something which will prevent such an incident important on a racing boat. Popping an oar can also cause someone to lose control of the boat, which may become an issue in heavy seas.
In some boats, rowlocks are attached to the gunwales. They may clamp on so that their position can be adjusted. In others, they may attach to outriggers. Different styles of boat feature different designs in terms of oarlock location and placement, depending on how people work while in the boat, and the purpose for which the boat is designed. Custom installations can also be made for specific applications.