Boats and ropes go together like eggs and bacon. Ropes (always called "lines" on a boat) are used to hoist and trim sails, hold things together, moor a boat to the dock, tow a water-skier and for many other daily uses. Handling lines requires a quick, secure and temporary way to fasten them down and, at times, quickly change their length or tension. Boat cleats are the hardware that allow boat crews to handle their lines efficiently.
Traditional Cleat (Open-Base Horn Cleat)
This is the most commonly seen type of boat cleat, used for all kinds of general line fastening. It's basically a thick "T" shape, with a hole in the centre of the "T" and a sturdy base for mounting to the boat. It's a versatile design; the arms of the "T" allow boaters to quickly secure or remove a rope, while the centre hole can be used as a completely secure, non-slipping mounting point for a critical line or even a load-bearing hook.
A bollard cleat is used for supporting large pulling loads. They are very quick to wind a line around, or quickly release one. Bollard cleats are characterised by a thick centre post (usually round or square), topped by a wide upper section to keep the line from slipping off the top. Some bollard cleats (particularly those used to secure an anchor line) have a pair of small protruding arms in lieu of a thick upper section. Bollard cleats are often used on the edges of docks to allow boats to tie up quickly. Many pleasure boats also have a bollard cleat mounted on the bow (front) to support the strain from the anchor line.
Jam cleats are almost exclusively found on sailing vessels. Sailboats rely on jam cleats to rapidly and smoothly change the length of a line in order to raise, lower or trim their sails. This type of cleat allows a line to be pulled through in one direction, but stops the line from moving the other way. Jam cleats come in two flavours, fixed and cam-action. A fixed jam cleat is usually made in a "V" shape with moulded teeth inside made to grip a line. A line can be pulled to the desired length, then tucked down into the "V", which will hold it in place until it needs to be adjusted. A cam-action jam cleat performs the same function, but uses a pair of spring-loaded jaws instead of a fixed shape to hold the line in place. Cam-action jam cleats bite harder the more the line is pulled against the jamming action. Because of this, cam-action jam cleats can usually hold against more force than a fixed jam cleat. Unfortunately, their moving parts can make them susceptible to wear or damage.