Sleipner, the curved fin that keeps you upright

The waves are at least two meters high, it is pouring rain, the wind is over 20 knots, and the temperature just above zero degrees Celsius. I always thought Scandinavians made boats that were too closed, that they didn’t realize how hot it is in the Mediterranean; today I changed my mind. I am quite happy to find myself well protected, indoors in the dinette with the webasto on and a cup of tea

by Niccolò Volpati

The boat is not Scandinavian, but British, a Fairline Squadron 65 and anyway I am not in the middle of the sea 200 km from Oslo to test it. What I have to test is Sleipner’s stabilizer fins. To be precise, these are the third generation, the result of many years of study and continuous testing on the many yachts on which they have been installed.


In fact, the Norwegian company introduced its first Vector Fins several years ago. The third generation of fins has been further improved. It changes the shape slightly, still sticking to the same philosophy and that is curved fins, not flat ones. They look almost like two foils attached under the hull, but their job is not to lift it out of the water but to reduce roll and pitch. Why do fins need to be curved rather than flat? Because they are more efficient and therefore can also be smaller.

Efficiency and energy savings in sailing

And what is the advantage? Less impact on the hull’s water lines when the boat is underway, and also less power consumption to run them. Two no small advantages. There are many different stabilization systems. There are the gyroscopic ones that have the drawback of being heavy and bulky and also consume a lot of power because rotating a ball of metal at thousands of revolutions per minute always requires a generator to be accessed.

The advantage is that they are positioned in the bilge and thus do not affect the hull. In addition to gyros there are fins, and electric ones have now supplanted hydraulic ones. They are more efficient, rotate independently of each other, and are positioned to significantly reduce roll.

Sleipner’s, precisely because of their shape, are very small and therefore undetectable in navigation. In fact, they are even active while sailing and thus help stabilize the boat not only when it is at anchor. During the test in the cold Norwegian waters I was able to verify this. In navigation no problem and a help that in wave passage I could appreciate. And then we proceeded with the most challenging test and that is the one stopped in the middle of the sea as if we were moored in the roadstead. Again the test was passed with flying colors. The difference between active fins and standby fins is remarkable.


Waves under control: the allure of smooth navigation

As I watch the oscillometer, which, thanks to the Sleipner inrterface, is reproduced on the Garmin plotter, I notice that we go from a roll angle that varies between 15 and 20° and one that always remains below 5°. The reduction is remarkable. With most waves, even if sideways, the sway always remains between 2 and 4°, practically feeling like being completely stationary. Only with the highest waves do you get to 5° and then feel the roll, which remains very bearable, however. This sensation, I must admit, I have always experienced with active stabilizers.

It applies to fins as well as to gyros, large or small. But Sleipner’s are precise and you arrange them with a laptop computer that processes the oscillation graph. What comes out is a picture that looks like the electrocardiogram when you had your visit to the cardiologist. In fact, the feeling is that my EKG is much worse than the Fairline roll with fins on, which is also why I’ve been putting off going to the cardiologist for several years.

(Sleipner, the curved fin that keeps you upright – – November 2023)