Rob says the argument for fins versus gyros has several considerations including the space that is required and the weight of the gyro, which comes in at around a tonne for a 60- foot motor yacht.
“The fins also rotate 360 degrees and will adjust left and right to counteract the roll and pitch of the vessel. The system detects a motion in one direction and paddles in the opposite direction to make the boat stay level, like duck feet paddling away below the surface.
“But it is worth noting only the stabiliser fins, not the gyros, work in conjunction with the trim tabs to keep the vessel’s ride level when underway.”
The gyro stabiliser takes about half an hour to spin up to full operating speed and about the same to wind down. A gyro works as if someone is holding onto the boat, reducing rolling left to right or pitching.
Fortunately, we don’t have to travel very far to find three experts in their fields at the Riviera factory. We firstly talked to Riviera technical writer Rob Partridge. Rob writes the owners’ manuals for Riviera motor yachts and truly knows the technical side of the boats.
Asked to explain both systems in layman’s terms Rob says: “The gyro is basically a large heavy metal wheel sealed in a vacuum environment that spins extremely fast. The reason it is sealed in a vacuum is to take out air resistance, which makes it spin faster.
“The gyro stabiliser works by spinning the flywheel which endeavours to remain horizontal. It
is on a gimble and always aiming to be level with the horizon forward and aft, and athwartships directions. If you can imagine a spinning top which, when spun, always tries to achieve the upright position.
“It takes about half an hour to spin up to full operating speed and about the same to wind down. A gyro works like someone is holding onto the boat, stopping it moving left to right or forward and backwards.”
According to Seakeeper, who makes the stabilisers, the flywheel can reach speeds of 557 miles per hour or just south of 900 kilometres per hour, depending on the model of the unit, which is dictated by the size of the vessel.
“The gyro stabiliser works by spinning the flywheel which endeavours to remain horizontal. It is on a gimble and always aiming to be level with the horizon forward and aft, and athwartships directions.”
Continuing our research into the secrets of stabilisers, we spoke with Riviera’s Final Quality Control & Sea Trials Manager Dean Brickell.
Dean is the final stage in quality control at Riviera. He and his team test and trial Riviera yachts on water to ensure the best quality control. He makes sure everything works before the yachts are handed over to the Riviera dealer and delivered to the owner. Dean has been instrumental in the sea trial development of both the gyro and fin systems on Riviera motor yachts and has practical working experience of the stabiliser systems both in local waters and while on extended ocean voyage passage making.
at Anchor
“Gyro stabilisers are good for an at-rest scenario, perfect for stabilising a motor yacht at anchor, with no moving parts on the external hull. The cost is reasonably similar, but the benefit of the fins at anchor is that they are run off the ship’s power and you don’t need a generator running like you do with a gyro system.
“And when you do consider that you need a generator running to power the gyro, you must consider the noise aspect both for you and your neighbours. Of course, the fins aren’t totally silent, they are moving around below the yacht keeping strain on your anchor, but if you do weigh up both systems in terms of noise, the fins are substantially quieter. The fin negatives include, while at anchor, the issue of people swimming around the yacht. So, it is always advisable to deactivate the fins if you have people in the water to avoid any wash or possible contact.”
Weight
“And then of course there is the weight of a gyro versus the fin system, the former being a tonne plus. With the latter 250 kilograms per servo motor – there is one servo motor which drives each fin per side – that is half the weight at 500 kilograms plus the extremely light carbon fibre fins. This also means less fuel consumption.”
Cruising THE REPORT | DEC 2024 | ISSUE 110 | 115
“If you are travelling at less than 10 knots the gyro works better, whereas the fins are effective at zero- speed mode which gives you stabilisation at anchor and at all boat speeds above 10 knots.”
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