Have you ever looked at the hull on a boat and wondered why it is shaped the way it is? Why do some boats have flat bottoms and others have V-shaped undersides of various angles and contours? Let us introduce the concept of deadrise, how it is intrinsic to V-bottom boats, how it affects the performance and ride comfort under various water conditions. Regardless of whether you are purchasing a boat, renting one, taking a ride in one, or simply watching boats from dry land, the mechanics behind deadrise are fascinating.
To adequately explain the concept of deadrise, we need to start talking about the boat bottoms and their shapes. To do so, you also need to remember:
- Not all boats have a deadrise angle. Deadrise applies to specific styles of boats (not including flat-bottomed boats).
- At times you may need to account for the deadrise angle when selecting what type of boat to use.
- That deadrise angle can affect how your boat behaves on the waters.
Boat Styles And Deadrise Angles: An Overview
The flat-bottomed boat is the most common and typically the cheapest type of boat for the entry-level and casual boater. These boats are simple to construct, easy to motorize, and tend to be very stable in calm waters. Thus, they are particularly attractive for slow-speed and stationary applications that rely on stability, such as angling, hunting, and wildlife photography. Examples of typical flat-bottomed boats: include cargo-ferrying river barges, the famous Venetian Gondolas, and punts (small boats used on calm, shallow waters such as canals, propelled or “punted” by using a pole to push off against the shore.) These boats are where the term “punter” is derived from!
The beauty of flat-bottomed boats is that they displace relatively little water, in effect sitting atop the surface or slightly submerged. This nature makes them particularly suitable for shallow water bodies and those with vegetation and muddy outcrops that can quickly cause a V-bottom boat to dig in and get stuck. However, this light-riding nature is their Achilles heel when waters get deeper and choppier. The flat nature provides a relatively large surface for the waves and dips of disturbed waters to rock the boat, resulting in a turbulent ride.
A savior enters in the literal shape of the V-bottom boat. A V-bottom boat rides deeper in the water, thus allowing it to cut through rather than merely glide on the water’s surface while also reducing its tendency to be rocked by choppy waters. But, of course, when stationary or moving at slower speeds, there will be some rocking motion, albeit at a much lesser degree than a similarly sized flat-bottomed boat would face in the same water. In addition, however, the V-bottom boat is more sensitive to sudden changes in onboard weight distribution than the flat-bottomed boat, which reacts the same but more slowly.
What about when you want some speed? If you were to push the throttle to full power, a flat-bottomed boat would skip like a stone as its bluff front generates a bow wave, catches it, rises out of the water, breaks the wave, and falls back — repeating the process as it propels through the water. This makes for a rather uncomfortable ride and also places undue stress on the boat. On the other hand, a V-bottom boat will maintain a bow wave as it continually pushes the waters to either side. As a result, the ride will become smoother at higher speeds.
Some observers may note that they have seen V-bottom boats skipping on the water. But if you closely observe the characteristics of those choppy waters, you'll see that they only “skip” when speeding head-on into the waves — for instance, when setting off into the sea from a beach or shallow waterway. Even then, they skip much less than a comparable flat-bottomed boat would under the same circumstances! Likewise, watch a V-bottom boat speeding across a relatively calm water body or one with perpendicular waves, and you will see how stable and graceful it is.
What Exactly Is Deadrise?
If you look closely at the “V” profile of a V-bottom boat, you will observe that: (a) it is angled, and (b) the angle is not uniform throughout the length of the boat. That angle is called deadrise, and boats typically have a sharper deadrise or steeper “V” at the front to cut through the water with less effort.
As we progress along the vessel towards the back, the deadrise angle decreases into a broader and more shallow “V” profile. Some hulls may even form into a flat-bottom or semi-flat-bottom type profile at the rear, offering a good blend of slow-speed stability in calm waters. These semi-flat-bottom type profiles provide improved control at higher speeds and increased ride comfort in choppy waters. For example, a small leisure craft may have a deadrise angle of approximately thirty degrees at the front with a gradual tapering to less than fifteen or even ten degrees at the rear.
Essentially, a sharper deadrise means that the boat sits lower in the water, thus making it less suitable for shallow waterways. A sharper deadrise also brings the waterline closer to the deck unless the boat is constructed with a taller profile than a comparable flat-bottomed alternative. In addition, deadrise also makes the boat more susceptible to the rocking that results from the motion of the occupants onboard.
Summary
Deadrise is the name describing the angle of a boat's hull. The next time you cross paths with a boat, take a few moments to see what kind of deadrise angle your boat has and how the hull and bottom profile match its purpose. If you plan to go boating through marshes, wetlands, and other shallow water bodies at a sedate pace while enjoying the scenery and relaxing, a flat-bottomed boat is your best bet. But if you require speed and want to cut through waves effortlessly, a V-bottom boat is an ideal option.
