Scandinavian brands are on a roll with advancements in stabilization technology. Zipwake, in Sweden, has introduced the Zipwake Pro with active control for pitch as well as roll. Sleipner, in Norway, is promoting its SPS 40 Vector Fins, which are part of an array of Vector Fins in the company’s catalog for vessels of different sizes.
The advancements are years in the making. Zipwake’s initial models, designed for boats from about 20 to 60 feet, were programmable to a point. The Zipwake Pro is almost aesthetically identical to the original model, but it’s five times faster with a reinforced pinion and with active pitch as well as active roll control.
Sleipner’s Vector Fins also have evolved and are of particular interest aboard larger boats seeking stabilization at anchor. Some models are designed for stability underway, either at planing or displacement speed, and others are meant for mitigating motion while on the hook, drifting or idling. In the middle are more intermediate models that can handle stabilization at idle and underway, such as the SPS 40 DC electric stabilizers the company recently promoted in a demonstration.
In fact, as we steamed out of Sleipner Group headquarters in Fredrikstad, Norway, aboard a custom 20-ton, 56-foot ferry converted into an excursion vessel, the SPS 40 Vector Fins seemed to react to seas more like active trim tabs or the Zipwake Pro interceptors than straight-fin stabilizers.
History in the Making
Trim tabs stood as the sole addendum to planing hulls for nearly seven decades. They level pitch and list, and they make for a faster, more pleasant, safer and more fuel-efficient ride. However, when they’re used incorrectly, things can get wonky or even dangerous very quickly. Unwitting passengers have been known to use them as boarding steps, and they can be a nuisance when fishing.
The first trim tabs were simple mechanical apparatuses implemented into German aircraft wings during World War I. These mechanisms were linked to levers and pulleys in the aircraft. They served two basic purposes: balancing control during flight, and serving as backup controls for damaged aircraft.
The nautical trim tab came along in 1959, thanks to Bennett Marine, and it was much closer in many ways to today’s hydraulic systems. The design has largely remained the same, with variations predominantly in the way of active trim tabs. These are programmed and make live adjustments as a boat pitches, rolls and lists underway.
Interceptors are some of the most popular systems. They lower the profile, reduce the number of articulating parts, and eliminate hydraulic cylinders. Until recently, though, they have been much slower than traditional metal plates and hydraulics.
Zipwake Pro on the Water
It was blustery enough that the twin 440-hp Volvo Penta 600s had trouble getting the 44-foot Targa tug out of the hole without the Zipwake Pro 600 E Series system engaged. The bow swung way up, leaving no view of the horizon and a deep bruise behind us at 12.5 knots, or just under planing speed. Engaging the $3,500 system from that position and speed, the bow dropped almost immediately, and we were on plane at 15 knots.
Coming out of the hole with the Zipwake Pro 600 E system (a 600-mm pair of interceptors) fired up and the blades set to automatic, we hit a cool 19-knot cruise in no time and never lost sight of the horizon. The 44-foot tug dug in deeper on turns, as if it were pivoting in place.
There are several shapes of blades within the Zipwake family. They include one rounded hull model, as well as four straight, three tunnel and four chine-hulled models. These have to be mounted at a distance from a propeller to prevent cavitation, but they can be much more tightly packed than trim tabs — something that’s becoming critical as boats are carrying up to six outboards.
And aside from the interceptor itself, there’s no exterior hardware, pistons or electronics exposed. The blades and other moving parts (a pinion) are encapsulated within two plastic plates, standing roughly an inch off the transom. That’s different from the foot or so that trim tabs extend. It certainly makes looking off the transom more pleasant.
Sleipner Vector Fins in Action
Sleipner Group has been an innovator since 1908, including in the bow thruster market for well over 40 years. Its Vector Fins are powered by brushless actuators, with motors built in-house that look a bit like drum brakes. The Vector Fins come in various shapes and sizes. Unlike traditional fins that resemble a pair of auxiliary fin keels and are limited in motion, Sleipner’s Vector Fins are curved, looking more like a sea turtle’s flippers.
The array of Vector Fins in Sleipner’s catalog is designed not only for vessels of different sizes, but also in various shapes with corresponding functions. The Vector Fins’ motions are informed by a gyro that dictates information to the fins, letting them do the work. A Seakeeper 5 was also installed on the on the same vessel we got aboard with the fins. We were drifting abeam to a 2- to 3-foot, three-second-interval wind swell coming across the North Sea, and our captain engaged and disengaged the Vector Fins. It was less than 10 seconds before the system worked steadily. I was able to roam the deck with both hands free.
We spent 400 seconds collecting data on pitch and roll with the Vector Fins, the Seakeeper 5, both systems combined and no stabilization at all. In short, each system did its job dutifully. The Vector Fins serve larger vessels, where a single Seakeeper gyro tops out at 115 tons, in the 85- and 110-foot range.
There are trade-offs with these technologies. The owner of a large, high-speed vessel that makes long hauls and rarely or never intends to navigate inshore shallows might opt for the fins. A slower trawler owner might want to keep external hardware and through-hull fittings at a minimum and rely on a gyro. Zipwake, Sleipner and other companies, including Seakeeper, Dometic, Quick, Hydrotab and Humphree, all offer options, creating a sizable marketplace for consumers.
