Zero speed stabilisation systems are designed to achieve minimum roll when a yacht is at rest, especially when out of the quiet confines of a marina. Without some form of stabilisation system, the superyacht experience will be characterised by discomfort caused by the yacht’s hull rolling with the waves – and this roll can get very severe in certain conditions. There are different types of stabilisation system available, and on new builds on yachts in the super or mega category, zero-speed is standard. Increasingly owners of older boats are having these systems installed. However, the nature of water is to roll, and all stabilisation systems are a compromise between passenger experience and performance cost.
Fin stabilisers are suitable for a certain hull shape of limited space. These fins can be retracted in a larger hull. Fin stabilisers are most efficient at cruising speed but do not contribute much to stability at zero speed, and there is always a trade-off between efficiency and drag. Gyroscopic sensing gears can serve to automate the process, and larger yachts with a long roll period may benefit from fin technology at zero speed. Fins apply a steady lift force which is useful for rectifying listings caused by a beam wind (blowing against a vessel from a direction at right angles to its keel), and downward wind rolls. Being internally generated, the impact of fin stabilisers is felt immediately.
Gyroscopic (gyro) stabilisers, mounted low in a boat’s hull, will also reduce a boat’s roll to a high percentage. The latest technology includes gyroscopic spinning in a vacuum absorbing movement and stabilising roll, creating a far more relaxing environment both under way or at zero-speed. Gyros are always located inside the hull where there is no risk of collision damage with debris or grounding. However, a gyroscopic stabiliser takes time to create a stabilising effect and contribute noise pollution when in full operation.
External zero-speed fins are excellent at creating stability. They are significantly larger than standard underway fins as they are required to move large volumes of water. The very size of these external fins does create more drag which has to be compensated by either augmenting engine horsepower or the acceptance of a slower top speed, combined with higher fuel consumption due to increased drag. Also worth noting is that being underwater, the repair process for external fins is more complicated than a retractable fin. The trade-off with gyroscopic systems is the relative quietness against drag and speed.