Boat Hull Design
by Alex Zidock Jr.


Flat bottom with soft chines

Flat bottom with hard chines

Flat-bottom boats

The one thing you can say about flat-bottom boats is that with their large bottom area, the boat is very stable in calm weather. Characteristically, however, the flat, broad bow area creates a rough ride. These boats are usually limited to low horsepower motors because they don't handle well at high speed. Flat-bottom boats are greatly suited for fishing in skinny water from the Susquehanna River to the Florida Keys, where a very shallow draft is a must.

Early in our nautical history, boats were powered by wind or by hand-stroked oars. Early boat designers found that boats went faster, and were easier to steer, if the bow was pointed. They also soon discovered that by lowering the center of gravity, the high sail masts had better balance, and usually kept the boat upright even in bad weather.


Tunnel vee


Displacment, planing hulls

These early boats were constructed with "displacement" hulls. This means that the hull would push through or cruise through the water. The proper propeller for a displacement hull is one with a lower pitch when powered by an outboard or stern drive. With the advent of mechanical power came boats with "planing" hulls, which lift the boat partially out of the water to skim on the surface. Today, it's sometimes difficult to tell the difference between the two, but there are slight differences. Propellers on boats with planing hulls often are not fully submerged, so they need to provide holding ability as well as higher pitch and rake, because of higher top-end speeds.


Vee bottom

Vee bottom with pad and strakes

Vee bottom with strakes

Round-bottom hull,"V" bottoms

The round-bottom boat has mostly a displacement hull and is usually used for dinghies, tenders, and some car-top boats. This boat style is usually easier to maneuver at slow speeds than the flat-bottom boat.

The "V"-bottom boat is probably the most common hull design. Most manufacturers of boats built today use modifications of this design. This design offers a good ride in rough water as the pointed bow slices forward and the "V"-shaped bottom softens the up-and-down movement of the boat. The degree of the angle of the "V" is called "deadrise." As the "V" shape extends to the back of the boat, it usually flattens out until it all but disappears at the transom. Some "V"-bottom boats have a flat surface at the very bottom called a "pad." This pad allows a little more planing surface and at the sacrifice of a little softness in the ride, but this addition increases top speed.



Tunnel bottom

Tri-hull, tunnel hull

There are many boats in Pennsylvania waters that are a distinct modification of the "V"-bottom that are called tri-hulls and cathedral hulls. The tri-hull boat is the traditional "V" hull with additional outside hulls. This design is more stable than the "V"-bottom at rest, but it gives a rougher ride in choppy water because of the increased surface at the bow.

Tunnel boats have been designed to trap a cushion of air beneath the hull to reduce drag on the outside hulls. This design is different from a catamaran bottom because the inner edges of the outside hulls have sharp corners to improve the handling of these boats at very high speeds. Many race boats are constructed with tunnel hulls and are sometimes called "hydroplanes."



Pontoon boat

Very popular in the Keystone State are pontoon boats. And just as the name implies, the pontoon, or deck boat, is a flat, raised deck supported with two outer hulls (pontoons) that are usually constructed of aluminum. These boats combine a lot of features of other boats. They ride very dry because the deck is raised above the floats. They are stable, and with the transom mounted to the underside of the deck, they are easy to maneuver with an outboard motor.

The boater who is looking for all-around use can make almost any hull design work for many water conditions. But even in the broadest markets, hull design is a continual research and development project. In specific niche markets, like water skiing, and now in the fastest growing of the water sports markets, wakeboarding, the competition for better hulls is tough.

When you are shopping for a new boat, first consider the water in which you'll use the boat. Then take into consideration how many people will generally use the boat, and then determine how the boat will be used. Boats come in a wide range of colors and cockpit configurations that you can live with if you like all of the other attributes the boat has to offer. But the one thing that should be at the top of your shopping list is what's on the bottom of the boat you want to buy.

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July/August 1999 Angler & Boater

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