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May 03, 2012

The Perfect Boat Hull

Decoding the mysteries of hull shapes in fishing boats

Regulators, like many fishing vessels, feature a single chine on each side of the boat. The chine usually forms a sharp angle — as sharp as possible with fiberglass. Inward from the chine is a flat surface — the chine flat — that might measure two to six inches based on the size of the boat.

Chines and the adjacent flat surfaces redirect spray to the side and create lift, Codega says. Beneath the hull, most fishing boats also have strakes that similarly knock down spray but also reduce friction.

“Strakes strip the sheet of water off the hull of the boat,” Codega says. “That reduces ­resistance and changes trim a little.”

The Speed Creed
Some companies take deep-V’s to another level, ­specifically those builders that make offshore-tournament center-consoles. Wylie Nagler, owner of Yellowfin Yachts (www.yellowfinyachts.com) in Sarasota, Florida, entered the tournament mix with a boat-racing background. His Yellowfins feature state-of-the-art-design technology, including a stepped running surface, a flattened pad near the transom and slightly wider, downturned chines.

Yellowfin also takes great care in considering fishing needs. “The old theory was the skinnier the boat, the faster the boat,” Nagler says. “Twenty years ago, people started putting center‑consoles on go-fast boats, and they found that the boat does go fast, but it doesn’t have any room. You need to have some room to have a well-thought-out fishing boat. There’s a ratio of length to beam that doesn’t hamper performance.”

Builders also play with the proportion between chine width (wider chines increase stability at rest), the pad design, and the step size and angle. The pad helps create better stability at speed. “If you look at the back of a ­conventional-V boat, it will be curved at the bottom or come to a knife edge,” Nagler says. “We have created something that’s 12 to 14 inches wide; it’s a V pad, not a flat pad. It means less deadrise in the keel, but there’s still a little to keep the boat from slapping.”

Steps introduce air, which reduces friction for better efficiency and speed — 25 percent to 30 percent better fuel economy and 15 percent increased speed, Nagler says. But some step designs work and some don’t, he explains, referring to the location of the steps and their angle. “When you’re running fast in a following sea, they can have a tendency to bow steer,” he says. “If a stepped hull is designed correctly, you cannot tell any difference in the handling of the boat from a conventional V bottom.”

Nagler says the steps in a Yellowfin hull are fairly shallow. In addition, rather than running perfectly straight strakes, he staggers them on the steps, which he says creates stability.

Lower and Lighter
Most bay boats and flats skiffs feature deadrise angles in the teens; 15 degrees is a fairly typical starting point. A slight angle helps skiffs run a little better in open sounds and in locations such as the mid-Atlantic, where inshore anglers venture outside the inlets.

“If I were selling bay boats from Cape Hatteras to New England only, I might have more deadrise and a sharper entry,” says Roop, who has designed Maverick and Pathfinder boats, among others. “If not, then I’d dial it down a little. A boat is not necessarily going to run worse if it has less transom deadrise. You wouldn’t want to use that one characteristic to drive your opinion.”

Deep-V hulls not aimed for the go-fast crowd often help prove this point. Roop says that in designing Cobia boats — targeting a broader demographic — he dialed down the deadrise angle to 21 degrees, making them flatter boats at the transom to reduce rolling.

“There’s still plenty of deadrise here, so you can run the boat hard and be very comfortable with it,” he says. “The width [of the boat] and the deadrise combine to make it run at the right attitude. That’s why I tell people to go run a boat to find out how it rides. If someone has done a good job designing it, they’ll be more comfortable.”

Outboard boats should run flatter, though in a following sea, they shouldn’t run too flat. Generally, Roop says, the flatter the boat runs, the less vertical acceleration it generates and the more comfortable it will be. However, Cobia boats were not intentionally built to run from wave top to wave top — as some go-fast hulls — but rather they employ a fine entry to slice through the waves for a soft ride.

The bottom line is that many factors work together to make a boat run properly. Don’t assume a specific deadrise number automatically pigeonholes a boat’s performance, Roop says. “My designs are all about finding the right running attitude,” he says. “The hull, the speed, the weight ­— all things have to dial in to get the attitude.”