Game of Inches
Imtra’s new Zipwake interceptor system is a small addition to your transom that can add up to big gains in performance.
I’m often amazed at how a yacht’s performance, especially a voluminous yacht with four staterooms, can be impacted by the smallest dimensions. An inch of pitch on a prop, pulling rudders in a couple inches, an added degree of deadrise—it’s the smallest margins that can mean the difference between exceptional performance or a dangerous design.
When I first held a Zipwake interceptor from Imtra in my hand, I was again astounded at how an aftermarket-ready device that lowers an inch and a half (when fully deployed) into the water from the transom could improve a boat’s time to plane, reduce bow rise, tighten its turning radius, improve fuel efficiency, and reduce roll when underway.
“It’s an interceptor so it’ll do everything your traditional tab will do for pitch control and you’ll also add in the fully automatic roll control system. You’ll get running stabilization,” said Jamie Simmons, product manager at Imtra. “Our most popular customer segment is [owners of boats in] the 20- to 60-foot range, but we’ve installed our system on a 100-footer.”
In my hand, the Zipwake 750—the largest interceptor the company offers—felt strong, but I was skeptical to say the least. I began to think about how to test the product. “We have a new Hunt Surfhunter 33 we can take out on Buzzards Bay if you’d like to see it in action,” came the offer from Jamie. I was in.
On a perfect summer day I followed Simmons to the helm of the Surfhunter, where he was going to show me how to set up the system. I dug through my bag for a notebook and pen. “Just turn it on, click English, imperial units of measurement, punch in your boat’s length, beam, and weight, and it’ll take about 15 seconds to calculate the pitch curve,” explained Simmons. Then eight seconds later, “OK, we’re ready to go.” I didn’t need the notebook after all.
It was a bluebird day on Buzzards Bay during our test. Meandering out to the bay at 5-ish knots our Zipwake interceptors were retracted, tucked up neatly behind the transom where no dock line—or fishing line for that matter—could find them and get tangled.
Once in open water I began a series of speed runs with the Zipwake system off, then on. After a bit of number crunching I recorded the following results:
2 GPH reduction in fuel burn at 22.6 knots (3000 rpm)
5 second reduction in time to plane
5 degree reduction in bow rise when coming onto plane
Again, we had near-perfect conditions that afternoon; less perfect for testing a device that reduces roll. For that I jumped from the Surfhunter to a Boston Whaler 22 Outrage that would rock and role more significantly. The Outrage was a great test bed; it leaned from side to side depending on where I stood. Activating the Zipwake, I watched the display that showed the interceptor fire off and retract at impressive speeds to keep the boat planted.
Full deployment of the interceptor took about a second and a half; that’s down from the five to eight seconds traditional trim tabs typically take to deploy.
There was one function of the Zipwake that perhaps impressed me the most. In the event of a loss of steering at the helm, you can use the interceptors to steer your boat home by manually lowering the tabs. That kind of redundancy would certainly give me peace of mind.
The ride was significantly smoother in the Whaler with the system on, and to my surprise the boat was much smoother in turns. When turning hard to port, for example, the port interceptor would fully deploy, thus allowing the boat to turn in tighter and tighter circles.
The ride was smoother, no doubt, but it’s no replacement for a stabilizer like a Seakeeper. I mentioned this to Simmons. “It’s not,” he agreed. He explained that Zipwake actually complements a gyrostabilizer. “A Seakeeper is great at low or slow speeds and Zipwake performs better when underway.”
Imtra has been installing this system on new boats like the MJM 35, and it’s received some high praise. But I see this system as a nice addition to a brokerage boat, as it could put some pep back in the boat’s step. If you’re handy and have a boat with a flat transom, Simmons estimates that it would take you 10 to 12 hours to install the system. If you don’t have a flat transom and glasswork is required it might be worth hiring a yard, he says. Cost varies depending on the size of your boat and the number of interceptors it needs, but, minus labor on a boat in the 20- to 40-foot range, you’re looking at a $2,500 price tag and closer to $5,000 on a boat closer to 60 feet.
My test of the Zipwake system showed what some might consider modest improvements to performance. A few degrees of bow rise, a couple gallons per hour of fuel, a few seconds to plane faster—when you add up all those benefits, it equates to a much more comfortable cruising experience. After all, it’s the little things that often make the biggest difference.
Imtra, 508-995-7000; imtra.com