Chines
Technically a chine is the junction of a boat’s topsides (the more or less vertical sides of the hull) and her bottom. On modern powerboats, there’s usually a defined ‘step’ here, running forward from the transom a few inches below waterline before sweeping upward to meet above the waterline at the bow.
Chines have several functions, including helping a hull to rise onto a plane and stay there, but the function most noticeable to the average boater is deflecting water away from the hull. ‘Reverse’ chines, which actually angle back upwards from the bottom of the hull side before meeting the boat’s bottom, do this best.
That’s easy to understand when you run your hand up along the bottom of boat with reverse chines in the way water would move upward if the boat were hitting a wave. The chine stops spray just the way it stops your hand. Although there are a lot of other factors involved, generally speaking the wider and/or ‘harder’ the chines, the drier a hull will ride.
So what’s the tradeoff? The main one is a rougher ride. Imagine the bow dropping down hard onto an oncoming wave. The vee-shaped bottom will ‘cleave’ down into the water relatively easily until the chines reach the surface and slow the downward motion. For the sake of argument, consider a hull with foot-wide reverse chines forward. When those chines hit the water while moving fast in a head-sea, you’re going to get quite a shock. Three- or four-inch-wide reverse chines have the same effect to a much lesser degree.
The chine (the flat surface at the outboard edge of the hull bottom) helps lift the hull onto plane and direct spray away from the boat. The topsides are nearly vertical, meaning the waterline width of this hull is only slightly less than the beam at any given point.
Flare
Widely flared bows function a lot like reverse chines, deflecting spray out away from the hull. In extreme conditions, they can also provide enough extra buoyancy to keep the bow riding up and over big, steep seas, rather than punching through them. They’re also pretty, at least according to most tastes.
Again, though, there’s a tradeoff. As long as the waves are small enough — and/or you’re moving slowly enough — that there’s no danger of actually burying the bow in one, a ‘finer,’ less-flared bow is likely to yield a better ride, since it tends to cut through the seas with less up-and-down bounce.
Deadrise
If you wanted to actually measure the deadrise of a hull, you’d hold a long straight-edge at right angles to the centerline so that it simultaneously touched the lowest point of the hull and the point where the hull bottom meets the chine. Then you’d measure how many degrees the straight edge was above horizontal.
Deadrise is customarily measured at the transom, where it ranges from zero degrees on flat-bottom skiffs to a maximum of about 25 degrees on boats designed for high speeds in rough water. Most planing-hull fishing boats have a deadrise between 10 and 24 degrees, with anything over 16 or 18 degrees qualifying as a “deep vee.”
All else being equal (which it never really is), a hull with more deadrise does less slamming, slapping, pounding, and so on than a hull with a flatter bottom. Think of the difference between whacking the top of a stump with a sledge hammer and an axe. To an obviously much lesser degree, the bottom of a deep-vee hull is like the axe.
On the other hand, hulls with more deadrise are less efficient and thus require bigger engines that burn more fuel. They also tend to rock more when not planing, which can make trolling and drifting less comfortable. Finally, poorly designed deep-vee hulls — and there are plenty of them out there — can be difficult to manage at high speeds.
Entry
The shape of the ‘entry’ of a hull, the point where the centerline meets the water’s surface, is also critical to ride quality, especially in head seas. Most of the unpleasant slamming experienced in rough water happens when parts of the hull that have been out of the water come back in contact with the surface. Thus, if the parts of the hull that leave the water frequently — the mid- and front sections — feature a relatively sharp vee, the boat should ride more smoothly.
The drawback to a ‘fine’ entry, though, is that it can give a hull the tendency to bow-steer, pulling to one side or the other as the sharp vee digs into the water. In following seas especially, constantly correcting for bow-steer can become tiring and, sometimes, downright dangerous. If you look at the hull of a Radon or a Davis, you’ll notice that the ‘forefoot’ — the forward part of the hull bottom — is remarkably flat. These are boats specifically designed to perform well in following seas, which makes sense on the West Coast, since in the afternoons, when conditions are generally roughest, we’re running downhill back to port.
The wide, reverse chines on this hull deflect water down and away. The fine, 58-degree entry means a softer ride in head-seas at the expense of handling in following seas.
Although they may not deliver as smooth a ride in head seas as hulls with a finer entry, hulls with a shallow forefoot, like this Radon 26, are more comfortable and easier to control in following seas. Photo courtesy Radon Boats.
Length-to-Width Ratio
Longer boats ride better than shorter boats, and narrower boats ride better than wider boats, all else, again, being equal. Thus, a hull’s length is (obviously) an important factor in ride quality, but so is its length-to-width ratio. Consider a 20-foot skiff with an eight-foot beam. Twenty divided by eight is 2.5, so the ratio of length to width is 2.5 to 1. For a 24-foot boat with same beam, it’s 3 to 1, and for a 30-footer with an 10-foot beam it’s also 3 to 1. For a 30-footer with an 8-1/2-foot beam, on the other hand, it’s a bit over 3.5 to 1.
If all four of those boats had identically designed bottoms, the narrower 30-footer would ride more smoothly than the wider one since it has a higher length-to-width ratio. The 30-by-10-foot hull has the same 3 to 1 ratio as the 24 x 8 hull, but should ride better just by virtue of its extra six feet of length. And the 20-footer will clearly the be the roughest of all with both the shortest length, and the lowest length-to-width ratio.
There’s more to it than that, though, since the dimensions that matter are not the overall length and beam, but rather the length and beam at the waterline. And two boats with identical beams can have significantly different waterline widths. The waterline width of a boat with perfectly vertical topsides will be the same as her beam, but if her topsides angle in toward the centerline, waterline width will be less than beam. Waterline length, likewise, can vary even in boats with identical centerline lengths.
The tradeoff here is an obvious one. Narrower boats simply are less roomy, and they also tend to rock more. And remember that when it comes to stability, it’s waterline width that counts, not beam from gunwale to gunwale.
Freeboard
Freeboard is the distance between the waterline and the gunwale of a hull at rest, and it varies over the length of the boat, generally increasing toward the bow. Freeboard doesn’t have a lot of effect on performance, aside from the fact that building higher sides on a boat adds some weight.
Freeboard, though, is related to cockpit depth, which is a big factor in safety, especially when small children are aboard. Simply put, the higher the sides of the cockpit, the less likely it as that children — or adults — will fall out.
The deepest cockpits on typical saltwater fishing boats are around 30 inches deep, and their gunwales rise to a few inches below the crotch of a six-footer. A 24-inch-deep cockpit is still comfortable and meets a six-footer a few inches above the knee caps.
Another advantage of a boat with high freeboard and a deep cockpit is that it makes fighting big fish standup-style — or even smaller fish in rough conditions — easier and more comfortable, since you can brace your thighs firmly against the gunwale. And of course higher freeboard helps keep water out of the cockpit.
On the other hand, many people find that they feel ‘closer to the water’ not only literally but also figuratively in a boat with lower gunwales. And of course, aesthetically speaking, boats that have relatively high freeboard tend to look ‘chunky’ and graceless alongside their sleeker siblings.