Tech Analysis: Hull Design

What makes a Powerboat P1 championship-winning hull? We attempt to find out...

When it comes to Powerboat P1 hull design, size definitely matters. As does shape. And rigidity. But, enough of the double entrendes. Just take a look at the different array of hull designs in the Powerboat P1 dry dock, and you’ll see that everyone has taken a different solution to how to design their boat. And – given how close the racing can be out on the ocean – they all can lay claim to having the right solution.

But, what are the key factors when picking or designing a championship-winning hull. One person who should know is #99 Fountain Worldwide 1st4boats.com team boss and throttleman Craig Wilson. As 2007 Evolution class title winners, Wilson and pilot James Sheppard dominated the fight for the crown with the new-to-Powerboat P1 Fountain SV40 hull.

“Obviously, all the boat builders have got a lot of experience, but a lot of boat design is ‘black art’,” Wilson says, explaining the boat designers’ dilemma. “A lot of boat design is still trial and error – for example, 1mm of angle change on the bottom of the boat can make it go 5mph faster or slower. Everyone will tell you their solution is faster. The proof comes out on the race course.

The basics of hull design are pretty simple. Hulls need to be as smooth as possible to ensure optimum water flow and minimal drag. As a result, they’re constructed from advanced, lightweight materials, such as carbon fibre, that don’t weigh the boat down, but rigidly maintain their shape. All the boat’s strength is in the hull, with the top decking effectively there just to stop water getting in.

Water conditions play a big part in how different boats perform, and obviously those vary from event to event, and even day to day. This is particularly true for the physical size of the boat. “A shorter, smaller boat needs less power to push it through the water, and is great at sprinting through flat water conditions,” says Wilson. “A longer, bigger boat needs more power to push it through the water, but goes much better in rough conditions. It’s about finding a good combination.”

And that’s where engine power comes in. Powerboat P1 is run to a strict power-to-weigh formula to keep competition close. More powerful boats, bigger-engined boats need to be heavier which adversely affects their acceleration and handling. Less-powerful, smaller-engined boats can be lighter and nippier. The ratios are 1hp per 3.5kg for the Evolution class boats and 1hp per 4.5kg for the SuperSport class, giving a minimum race weight for each boat based on its horsepower.

The difference between heavy and light boats can be as much as 1.5 metric tonnes – the equivalent of a medium-sized car, or nearly 20 extra people on board. Just look at the above picture of the powerful, diesel-engined #60 GFN Gibellato boat racing the smaller-engined #99 Fountain Worldwide boat to see the comparison.

“A big, heavy boat handles better on rough water, but will struggle a bit in calm waters,” Wilson explains. “It’s also harder to trim and balance for optimum performance while you’re racing. A smaller, lighter boat has better acceleration and handling, and you can always add static ballast to optimise the handling. Last year, all the boats had very similar top speeds, and we’d go down a two-mile stretch side by side. It all came down to who could turn into the corner hardest and accelerate out fastest.”

The final factor in hull design is steps. If you look under the hull, you’ll notice steps, or sharp breaks in the contours of the hull design. When the boat is moving through the water, these suck air in, making a lower-friction area that allows the boat to skim faster over the sea’s surface. Different designers favour two, three or even five steps, but this is still a real subject of debate and another of the ‘black art’ areas of boat design.

“Fountain founder Reggie Fountain pioneered step systems, and reckons that two is best,” says Wilson. “Skater and Outerlimits have three and five-step boats, the theory being that the boat runs flatter to keep more running surface in the water. But Reggie would say that’s wrong, because it creates a vacuum, making a more turbulent pocket of air. Again, all boat builders have different thoughts and solutions.”

And that’s where the beauty of boat design lies. Even if a budding title winner wanted to copy the design of the reigning champion team, they couldn’t. Because what works for one boat, doesn’t necessarily work for another. All adding to the intrigue that makes Powerboat P1 such a fascinating sport.