Inside Angle: Tales From a Tank Test - Power & Motoryacht

Computer simulations have come a long way for -naval architects in the past several years, but nothing can replace a traditional tank test when it comes to truly understanding a given hull design’s performance before the full-size vessel is built. On these occasions, a client and I will visit a dedicated tank test facility like the 315-foot-long pool at the Stevens Institute of Technology in Hoboken, New Jersey, just across the Hudson River from Chelsea. Clients love to come along for fun like this. I mean, there’s a model involved! It brings out the kid in everyone. And one way or another, something weird happens every time.

A few years ago, my office was designing a 130-foot motoryacht for an American client with a specific speed target in mind. As is done in situations like this, we had a 7-foot-long scale model built and shipped to the academics at the Stevens Institute. First-time clients are invariably excited at the start of a day of tank runs, but after 20 runs at 1-knot increments, it can get downright boring. So on this day my client asked if we could spice things up a bit.

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The boat’s target speed was 26 knots, which is sprightly for a 130-footer weighing nearly as much as a fully-loaded Boeing 767. But 70 yards downrange of the guys running the tank, my client whispered in my ear, “Can we run the model at 50 knots and see what happens?”

I had designed the hull bottom to handle speeds greater than 26 knots, both for good seakeeping and in the event more yachts of this design were built with larger engines in the years to come. Among other things, her forward sections were finely tapered. The chine was pulled back so it met the static waterline farther aft than a typical, porky motoryacht hull. I wanted to see this, too.

I nodded to the client and turned to take the long walk past 90 years’ worth of historical hull models hanging on the wall to confer with the scientists at the controls.

“Guys, are we going to break anything if we run the model at 50 knots?” I asked. I could tell by their wide-eyed expressions that they were not accustomed to this sort of engineering debauchery. They thought about it for a long moment, looked at one another and then said, “Probably not. Let’s try it.”

Like a pit crew, they sprang into action, double-checking the fasteners on the expensive overhead gantry which would propel the model (and what looked like $1 million worth of testing equipment) at the scale equivalent of 84 feet per second. They hastily calculated this speed and punched it into the bank of computers. I hurried back downrange to the client, who by now had his phone in front of his face, shooting video.

With heightened vigor the tank facility manager announced “50 knots! Three, two, one!”

The long, narrow concrete block chamber around the test pool exploded in sound, the overhead gantry’s mechanism howling in pain as the model reached its terminal velocity. It sounded eerily like the real boat might, if the real boat had the 15,000 hp needed to reach these speeds. And the hull shape looked perfect flying atop the water, like this expensive yellow hull model had found its true calling.

The client was so captivated by the ferocious speed and sound, and the beauty of the event, that his phone flew out of his hand as the 7-foot boat shot by, spinning and splashing into the tank and quickly sinking to the bottom as the thunderous roar of the gantry gradually wound down.

There was another long walk back to the guys at the computers. And a round of drinks on me at the end of the day, after a trip to the Apple store on Prince Street.

One way or another, something weird happens every time.

This article originally appeared in the October 2020 issue of Power & Motoryacht magazine.

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