You may think you know what a "chine" is and where it is located on a boat, but finding a clear definition of chine can be difficult. You will find everything from religious references to a part used in medieval cart wheels. To further complicate things, boaters frequently confuse a chine with a spray rail or lifting strakes. So here is a simple explanation regarding chines and why they are an important part of your boat.
A chine is the section of a boat where the sides of the hull intersect with the underside, or bottom of the hull. It is commonly identified as the place where there is a sharp angle change in the cross section of a hull. It is this significant angle change in the hull of most modern pleasure boats that is defined as the chine of the boat.
Okay, that explains where a chine is located on a boat. But more importantly: what is it and what does it do?
In the design of early boats, the transition from a boat side to a boat bottom was not a sharp angle at all, but rather a smooth curve. Boats with this seamless curve design make it difficult to know exactly where the sides end and the bottoms begin. For planing boats that wanted to transition from a displacement boat to a planing boat, this rounded bottom provided less lifting action and planing surface than was practical. But, while flat bottom boats would solve that problem, they proved to deliver a very rough ride in choppy water. So a compromise was struck. Boat designers introduced chine curves that were reduced in diameter and called them "soft chines."
Chines might still be following this soft chine design if it were not for the invention of the deep-V hull. As more powerful engines evolved, experience showed that if the bottom was more pointed towards the keel in design, the more powerful boats could rise even higher out of the water, reducing drag and increasing speed. With the ability to deliver higher speeds, deep-V hulls grew quickly in popularity.
But there was a problem.
Boats that rode on a more pointed than rounded surface proved to be unstable and would list to one side when on plane. Designers even feared that they might fall over onto their side in the hands of an all but experienced boater. The solution was an obvious one. Put a little bit of 'flat bottom' back into the hull. The best location for this small flat section proved to be where the sides meet the bottom -- the chine. It didn't take much of a flat spot to do the job and the modern V-bottom became the design of choice. This is how the chine on most modern boats (i.e., the place where the sides meet the bottom) came to include a small section of flat surface, one or two inches in width. This small pad at the chine creates the higher vertical pressure that allows the hull to get onto plane faster and to stay on plane at lower speeds.
Because all designs continually evolve, some chines are now molded to go beyond flat and actually point downward on the outside and in the process trap more water. These are called "reverse chines," and they provide even greater lift. A reverse chine permits a steeper V-bottom. The sharpness of the point in a V-bottom is usually measured in degrees and labelled as deadrise. In case you have forgotten, deadrise is defined as the amount of angle that forms between the boat bottom and a horizontal plane on either side of the center keel.
I shouldn't talk about a chine without defining the popular term "chine walk." In truth, chines do not walk at all. Rather, it's the boat that sets up in a walking motion from side to side. How does this happen? When a chine on one side of the boat dips more than normal into the water, for one reason or another, the boat will react by lifting (rolling) in the opposite direction. The driver must quickly correct this motion by steering an equal amount in the opposite direction. Failure to make a prompt steering correction and the chines on either side of the boat will increase their lift oscillations until finally the boat becomes uncontrollable. The best solution, should you experience chine walking, is to throttle back to an idle until the boat returns to a stable track.
Some modern chines deliver an added benefit. They help deflect the spray that can run up the side of the boat and splash occupants. While this is often a listed benefit of chines, it is not the same as a dedicated "spray rail." The pure definition of a spray rail is a longitudinal addition of varying lengths to the hull section of a boat, with the purpose of knocking down a spray that might otherwise find its way into the boat.
Many boaters consider a chine to be a "lifting strake." If a chine is not a lifting strake, where do we find lifting strakes? Try looking on the bottom of the boat. They are the long linear protrusions that run longitudinally on both sides of the keel. With their small but additional flat surfaces, lifting strakes are major contributors to raising the running attitude of boats. By raising the hull further while keeping the boat level, they increase top speed. The only negative aspect to these strakes is their added weight and the increase in the boat's total area of wetted surface. Every boat builder has a different opinion as to how many and what shape their lifting stakes should follow.
A "spray rail" reduces spray. Believe it or not, some hull designs do a bang up job of washing down its occupants when running in anything but flat water. That is one of the good reasons to always test drive before you buy. Enter the dedicated "spray rail." While some chines help limit spray, some don't. Such boats usually add some form of wing like protrusion to the side of the boat that will deflect unwanted spray.
Being clear on the purposes and differences between a chine, a lifting strake and a spray rail should serve to raise your level of general boating knowledge. #tips