STEADY AS SHE GOES…
In the world of stabilization technology there is not one size fits all. Sleipner discuss the options available dependent on vessel size and projected usage.
For naval architects and boat builders, choosing a stabilizer system has traditionally meant making some tough choices. How much stabilization force can be achieved before the impact on speed and fuel consumption becomes unacceptable? Additionally, it’s not always clear what type of stabilization to choose, as the two leading technologies (fins and gyros) have significant functional differences.
Understanding the basics
Gyro-type stabilizers are installed inside the boat and get their total roll reduction force from the precession motion they generate to resist a boat’s roll. This also means they have the same absolute force regardless of wave period and boat speed; when the precession motion reaches the end of its travel, there is no more force available in that direction.
Fin stabilizers act in the water and have two ways of creating roll reduction force, depending on the boat’s speed. At zero speed, the fins rotate rapidly (flap) to generate force and, like the gyro, have a definite limit and stops when they reach the end of their travel.
However, when the boat moves forward, fins also generate roll reduction forces by the angle at which they pass through the water, like adjustable airplane wings or underwater foils. This force increases by speed squared, so the faster the boat moves, the more force they generate. Crucially, they can hold this force for as long as the boat keeps moving forward.
The invention of the curved stabilizer fins has, by some, been called a stabilizer revolution. This simple but highly effective solution eliminates many of the traditional trade-offs naval architects and boat builders had to accept in the past. Vector fins™ create lift underway, reducing the boat’s hull drag by approximately the same amount as the drag the fins create, making it a break-even scenario. In some cases, this even results in a small gain in speed and fuel efficiency.
Key things to consider when choosing stabilizer technology
• Choose stabilization technology to match the boating the owner will be doing.
• Check the practical limitations – not all systems will fit all boats, mainly due to space limitations.
• Consider what is best suited to your boat and what is likely to retain the most value when the time comes to sell – some sizes and yacht designs lean more towards one technology.
Spin it or fin it?
If your only priority is zero speed stabilization, the gyro will work just fine. However, suppose you also use your boat on longer cruises and want to have excellent stabilization when cruising in the open sea between sheltered anchorages. In that case, fins have a colossal force benefit. They can reduce or eliminate many times the wave height and length of a gyro of this size.
You can, of course, choose a bigger gyro (or multiple smaller ones) to increase the cruising capability, but this is when size and weight start to make an impact – to match the fins at eight knots, you need to more than quadruple the size of a gyro. Alternatively, you can choose bigger fins to match the gyro performance at zero speed.
There are undoubtedly many other considerations when choosing between the principles of fins or gyro stabilizers, and yet more to weigh up when comparing different brands. Still, it ultimately comes down to having enough force available when you need it.
For more details Tel: +47 69 30 00 60 or visit www.sleipner.no