A skeg is employed in the type of kayak used on more open water such as the sea. Its purpose and use are rather different from those of the surfing skeg. In the kayak, the amount of exposure of the skeg to the water, and also its effect on the position of the boat's centre of lateral resistance (CLR), is freely adjustable by the crew. The adjustment varies the degree to which the wind affects the boat - that is, the amount of lateral movement the wind can cause by impacting the upper parts of the boat and the crew.    In more conventional calculations, this would be the centre of effort of the sail area (CE). In still water, where the wind is pushing the boat sideways, a contrary force (lateral resistance) develops, resisting that movement. If the central points of the application of those two forces coincide, the boat moves steadily sideways. Otherwise, it rotates in the horizontal plane, until they are in line. By varying the CLR, it is possible to better control the boat's attitude towards the wind and waves. Irregular flowing movement of the water complicates the issue, however.  This link explains the subtleties of the kayak skeg. They may be made of wood, fiberglass or aluminum. Some are deployed using internal cables, but others use external ropes and bungee cord . Typically, these are retractable, and they are not a rudder.     If properly configured (., use of street sign aluminum in a narrow box that extends through the hull) they will not flex, and will greatly decrease and counter pitch , Roll and yaw , like a centerboard on a sailboat, when the craft is moving. In that sense, the skeg acts as a lifting foil .
A patent granted to Jonathan Brownill, a cutler from Sheffield, on 1 May 1828, while in principle operating as an open-air balance lock , was described as using three caissons . The main caisson was connected by ropes passing over grooved pulleys to two smaller, counterbalancing caissons. Brownill's innovation was to place wedges ("inclined planes") opposite the upper and lower fixed openings so that as the main caisson moved into place, powered by water being added or released from the counterbalancing caissons, rollers acting against the wedges forced it against a padded frame surrounding the opening. The "conductor" was to have control of a lever to release the rollers when the vertical gates were slid shut for the next ascent or descent. 
The shaded Outboard Profile drawing shows the bowlight/fairlead but lacks construction detail. It does show frame locations along with the base line, and lines drawn along the deck and keel intersect about where frame 0 would be. The front of the bowlight/fairlead is about 3" behind this point. This accounts for the difference when looking at the drawings. Extreme measured length would actually start 3" behind the deck and keel conjuncture at frame 0, and end at 966" when looking at the drawings. This, and where exactly midships was, stumpted me for a while so I wanted to mention it for the benefit of any also wondering about the seeming discrepancy.