Stabilisers: How to prevent boat rock and roll

With thanks to Bennett Marine

A stabilised superyacht significantly enhances comfort and rest for both crew and guests. This means that individuals are a lot more rested making better decisions and more enjoyable experiences. The marine industry has a number of stabilisation systems available for a yacht or boat to eliminate ‘boat roll’. However with a large number of options all demonstrating different advantages and disadvantages, knowing which is best for the yacht can be difficult.

What stabilisation systems are available?

Stabilisation made its way into the marine industry when it was realised that stability at sea and seasickness needed to be minimised to essentially continue to attract new customers.

There are three main types of stabiliser systems available and all have their pros and cons and all vary on what boats they work best on.

Fixed fin stabilisers

The fixed-fin stabiliser is suitable for hull shapes where the fin will not protrude beyond the rectangle of the ship’s frame. Fixed- fins are commonly used where space within the hull is limited.

Retractable stabilisers

Fins can be retracted to inside the hull as to combat some of the disadvantages of a fixed fin. Control of fin movement is automatic and is usually derived from gyroscopic sensing gears.

Gyroscopic (gyro) stabilisers

Mounted low in a boat’s hull, gyroscopes will reduce a boat’s roll significantly. Today’s control–movement gyros are spun up inside a vacuum to eliminate air resistance and lower power requirements.

Gyro stabilisers vs fins stabilisers

Much has been discussed about which stabiliser is better at reducing boat roll. Here are advantages and disadvantages of each system.

• Because of their drag at speed, fin systems are not suitable for planing hulls. Fin systems are speed dependent, always balancing fin size with projected cruising speed. This create minimum drag for desired performance. The result is that at zero speed they have no effect (except on very large yachts with long roll periods), and at less than cruising speed, performance drops off sharply.
• Fins can correct small steady/static heels or listing due to beam winds, off center weight or long period rolls running downwind due to their inherent ability to apply a steady lift force under the hull while the vessel is in motion. In contrast, gyros cannot supply constant forces and as a result cannot correct a heel or list angle.
• Because gyro stabilisers require no protrusions from the hull, it is not subject to damage from grounding, or impact from floating debris.
• Fin stabilisers work immediately whereas gyro systems have to ‘warm up’ to be fully effective. Seakeeper’s 5 gyro stabiliser takes 35 minutes to spool up to 9,035rpm, the point at which it provides stabilisation, and another 15 minutes before it reaches its full 10,700rpm. Compared with instant-on fin boat stabilisers, that’s only going to be a drawback
• External zero-speed fins are considerably larger than standard underway fins as they must actively move large volumes of water to stabilise a vessel. These oversized external appendages result in significantly more drag and must be compensated by increasing engine horsepower or acceptance of a slower top speed. In addition, external fins negatively affect fuel efficiency due to the additional drag.
• As fins are submerged this makes them more difficult to repair, which generally means repair costs increase. Gyros are always located safely inside the hull where there is no risk of damage.
• Gyros have a certain amount of noise pollution in comparison to fins and may be heard when in full operation.

Which stabilliser suits you

High speed sport yachts

These would benefit most from a gyro system. The gyro systems are good because they don’t require mounting external fins and generally need only electrical power and room to mount. Having no fins reduces drag in the water resulting in a higher speed.

Trawler type boats

These will most likely suit active fin stabilisers as their first line of stabilisation technology. If your full displacement or semi–displacement hull is not currently stabilised, the improvement in ride and the way you feel after a long day in heavy seas will amaze you. These are expensive and will put a dent in your wallet but it is value for money especially for long–distance cruising.

Boats at anchor

To reduce roll at anchor, yachts would require a form of zero-speed stabilisation. Some good stabilisation systems available include an enhancement to your existing fin–stabilisation system to enable at–anchor control; a gyro system, which can also be used at speed; or a flopperstopper, which might be adequate enough for smaller boats in quieter anchorages.

It is essential to talk to as many people and manufacturers as possible before making a decision. Many companies can offer warranties and guaranties along with their products so research would definitely be worth the time.

Download stabiliser tips as PDF.

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Want to know more yacht stabiliser tips? Read our guides here. Alternatively, you can search for yacht stabiliser companies here.