Taylor Made: Awaken
In early January, when the northern storm cell swept into Illinois and worked Lake Michigan into an angry sea, I went to the shoreline to take stock of the waves. I was not disappointed; frigid water had danced right up the beach to the edges of the woods. Yet the waves that had me laughing with glee would pale to those of the ocean on any decent day—it might have behooved lake dwellers to stay off the water that day, but an ocean vessel would not blink.
For ships, design considerations such as purpose of the vessel and type of cargo (or passengers) can later be discerned from a visual inspection of the vessel in its port. I could go to Belmont Harbor in the summer and take note of all the different styles of sailboats and houseboats docked. However, it is easy to miss a crucial element: the hull. Ships are designed for the conditions they will operate in, including those experienced at the hull-water interface.
The draft of a boat is the vertical distance between the waterline and the keel, or structure along the centerline of the hull. This can give an idea of how much of the boat sits underwater, which matters for buoyancy (recall that buoyant force depends on volume of displaced water). However, it does not tell us about the profile of the hull. Neither surface area of the hull nor volume of water displaced gives us a concrete answer for what the cross section might look like. Instead, we need a third element. The chine describes significant changes in angle along the cross-section of the hull, shedding light on its profile. The chine could have a distinct shape, like an “S”; it might simply be soft, meaning more rounded, or hard, meaning sharp.
For deep-V hulls, the chine forms a “V” shape. This type of design is common on motor-powered pleasure craft, such as the speedboat you might have gone tubing behind. Deep-V hulls allow for better speed and acceleration and cut well through choppy water at slower speeds, but tend to bounce in waves when traveling at higher speeds. By contrast, pontoon hulls, which are essentially cylindrical, ride nicely on top of rough water at higher speeds. However, these hulls can get tossed around at slower speeds and have less precise handling response at idle.
The extended hull of a deep-V means more surface area, requiring additional power from the engine to overcome friction. These hulls are designed to plane after a critical speed, meaning that the front end of the boat rises from the water and “hovers” over it as the boat drives. Keeping the nose end relatively flat but still out of the water decreases the potential for a bow wave, or wave that acts against the boat’s motion. Bow waves are the result of disturbances in the fluid flow caused when an object moves through the fluid surface at greater speed than that of the fluid’s waves. For boats, bow wave profiles are influenced by factors such as draft, depth of the water, and shape of the bow. A common method to address this occurrence on larger ships is to add a bulbous bow, where a bulb-shaped appendage sticks out from the bow just below the waterline to reduce drag around the hull.
Just as airplanes must be balanced so they sit level in flight, the boat must also be balanced to sit correctly in the water. The placement of the engine in relation to the shape of the hull, for example, matters for center of gravity, so the hull cannot be designed without consideration of many other characteristics and needs. This is another good reminder that effective engineering does not happen in a bubble; it requires strategic pooling of resources and expertise from different disciplines and backgrounds.