sailboat bottom fin
A keel is easily recognizable as a flat blade that comes down from the bottom of the boat. it can vary in size and shape depending on the make and model of the boat. but, generally, it will look very much like a fin. if you imagine the fin on the underside of surfboard you will have a pretty good idea of what it looks like under the boat.. The hull comprises the the bottom, topsides, buoyancy tanks, and deck. keel a weighted fin that, when attached to the bottom of a sailboat, keeps the boat from capsizing or slipping sideways in the water, which allows it to sail upwind.. A skeg, (skegg or skag) is a sternward extension of the keel of boats and ships which have a rudder mounted on the centre line. the term also applies to the lowest point on an outboard motor or the outdrive of an inboard/outboard. in more recent years, the name has been used for a fin on a surfboard which improves directional stability and to a movable fin on a kayak which adjusts the boat's. 
sailboat bottom fin Fins on either side of the boat stick out into the hull envelope, which is the area of water that would be contained if lines from a boat’s keel and gunwale met to form a right angle below the water. charles egan, naiad’s technical documentation engineer, says that from there “an electronic motion sensor [detects] even the slightest bit.
