Dr. Pat Benz,
PhD

What is a PhD organic chemist who doesn’t really sail doing building a 72-foot catamaran that actually flies over the water, at speeds never seen before in an ocean-going catamaran?

It started with a half-finished Gunboat 66. Gunboat went bankrupt in 2014 with the boat only half completed, and I brought her back to California, to Morrelli & Melvin, who were the original designers of the Gunboat 66. She came down the 405 at two in the morning to a small boatyard in Costa Mesa. She had no daggerboards or mast yet, so after many discussions with M&M I decided to make big alterations. I wanted a big wing mast and a large C-foil instead of a straight daggerboard.

With a tall wing mast and a large C-foil we were doing 23 to 25 knots fairly easily, and our maximum speed was measured at 31 knots. In 2015 we were the first catamaran to finish the Transpac and won the Rudy Choy Trophy. I didn’t sail her; I was on board as the cook, which I love to do, and the professional crew loved my cooking as well. She was very comfortable too, with a full galley, hot showers, real beds, an automatic espresso machine and even air-conditioning. With all that, we were still the first catamaran to finish.

That boat showed me the limits of having a single board do two completely different jobs: leeway and lift. From 3 to 12 knots of boat speed the C-board was slightly worse than a straight centreboard. From about 13 to 22 knots it performed well, and at 23 to 25 knots its lift fraction was about 30%. As we went faster, the C-foil pulled the boat to windward, and that made the helm a difficult job.

Several years later, after I had sold the original Extreme H2O, I met Pete Melvin and Ferdinand van West at an Italian restaurant in Sarasota. I asked if they would be interested in a complete redesign: a boat correctly balanced for speed, but keeping all the comfort of the original. That was the beginning of PB72. The design, and all the thought that went into it, is what I really enjoyed.

To balance the boat and keep the same saloon, she had to be 72 feet, with the mast moved back to the top of the roof. She needed to be wider, with a waterline close to 72 feet, and the entire boat had to be carbon and Nomex. Then we talked about foils. No one except me wanted two boards per side; the complaints were that it was too complicated and too heavy. I insisted. I wanted to separate the two forces: one horizontal, to windward, for leeway, and the other vertical, for lift.

At first she was designed for 50% lift, and everyone but me thought that would be the limit for control. We continued. M&M and North Sails used an interactive program to “sail” the boat in six degrees of freedom. It was very costly to run and took time to produce the data. When we reached a 50% lift fraction the boat was stable in the program, so I wanted more. It felt like I was spending $100,000 for every 10 to 15% of lift fraction, until we reached 90%. Then we went for 100%, and she appeared stable in calm water. But it became clear that the most stable condition is just skimming the water, at 80 to 90% lift, depending on the waves.

The result is a righting-moment foil that can lift the entire boat, working from a point five to six feet to leeward. The boat stays almost level at these speeds, which the program shows exceeding 40 knots. As well as two foils per side, we adjust her attitude like an aeroplane, with large T-foil rudders on conical titanium bearings that let each rudder move fore and aft to bring the bow up or down. There is nothing forward, because at these speeds the sheets and the crew need to be back behind the roof.

In her first and second sea trials she has shown what she can do: 27 knots in 11 to 12 knots of wind at 110 degrees, 38 knots in 18 knots of wind at 130 degrees, and 39 knots in 20 knots of wind at 85 degrees.

We designed an open-ocean catamaran faster than any other catamaran.

Dr. Pat Benz