Superyacht Stabilization Options


It’s unusual these days to come across a newly built yacht of, say, 60ft plus, that does not have some form of stabilisation installed. The more interesting fact is that an increasing
number of smaller yachts and boats, even in the 20ft to 30ft plus size range, are enjoying the benefits of a stabiliser solution. For professionally crewed superyachts, today’s scenario is that not only can the mother ship have stability under control, but her tenders, chase boats and shadow boats can enjoy the same kind of calming measures too.

Whether displacement, semi-displacement or full-planing motor yachts, it’s those tall superstructures and high centre of gravity that makes motor yachts more susceptible to the uncomfortable effects of waves, either at anchor, moored in a marina, or when cruising in the open sea. For the industry to continue to prosper, owners and their guests need a level of assurance that their sea-going experience is going to be as comfortable and, ultimately, as enjoyable, safe and successful as possible. Once mainly the preserve of gyros and fins, a number of new and alternative stabiliser solutions have since emerged.

Primarily designed to counter the age-old problem of nausea, leading to full-on motion sickness, stabiliser systems often claim a number of secondary benefits, such as, for example, improved fuel consumption and increased boat speed – the level and scale of which is something for the customer, ultimately, to decide.

Whereupon stabilisation had previously only been available for yachts down to a length of about 60ft / 18metres, today’s wider choice, and the burgeoning retrofit market, has meant that owners of new and used boats, even in the 20ft to 30ft size range, are enjoying the same or similar roll reduction benefit, as for larger boats.

Seasickness and how waves affect a hull
Sea and waves impart six different forces on a hull, namely, heave, surge, sway, pitch, yaw and roll. Of these effects, roll is one of the most influential causes in the case of passenger discomfort. Tiredness often ensues, leading to nausea and, in many cases, full on seasickness.

Roll is exacerbated by the boat’s own inertia energy, the effect of which makes a boat roll even more than the angle of the wave itself. The result is large movements of the head in the form of sudden accelerations from side to side. The boat’s own momentum takes over and increases the sickness-inducing effect even more. The vertical, up and down pitch of a hull has also been highlighted as one of the main causes of seasickness. The logical reality is that it’s more likely a combination of all six effects, with each contributing to a greater or lesser extent.

And, although it’s true that, for many people, the body does eventually regain itself over time and becomes more accustomed to the uneven motions and nausea, getting to this point is without doubt one of the most miserable times for anyone on a boat, when all you simply want to do is get yourself back on dry-land as quickly as possible!

Based upon the simple premise that an upright and properly trimmed hull is working more like its naval architect intended it to do, the other major reason for investing in an appropriate stabiliser system for your hull type, is additional savings on fuel for the kind of typical boating you prefer to do.

A yacht at sea moves in six degrees of motion, simplified, it means that it is free to move up/down, forward/backward, or right/left and its ability to rotate around its three axes. these movements are known as heave, surge, sway, pitch, yaw and roll.

Alternative stabilisation technology
Courting publicity and winning awards within the marine market, several relatively new ideas for boat stabilisation technology are now being used. Foils, for example, are a version of the fin, yet with full articulation, allowing them to be swept back and forwards and (in some cases) fully retracted within the outer confines of the hull. Foils deflect the flow of water, exerting an upward force on the foil, thus creating lift, which increases with boat speed.

The Dutch company, DMS, for example, have developed an ‘all-in-one’ foils solution that when mounted on the transom can rotate like traditional fins at cruising speeds, can flap up and down in the vertical plane at zero speed, or can be retracted fully back, to act as active trim tabs.

Rotor stabilisers are based upon fast spinning cylindrical tubes, that when protruding one either side of the hull create lift, referred to as the Magnus Effect. Instead of protruding at a 90-degree right angle to the hull, these can be raked back for less resistance at higher cruising speeds. A secondary benefit is a back and forth action, which, when deployed correctly, gives stability at zero speeds, yet without creating the ‘swimming’ effect of slowly paddling the hull in a forward or backwards direction.

Another emerging system is from Hull Vane, who have developed a patented static, wing-shaped appendage, or underwater spoiler, fixed across the full width of the hull at the rear.

Said to be particularly effective against hull pitching and slamming, the wing is designed for displacement and semi-displacement hulls, effectively converting stern wave energy into forward thrust, the benefits claim to be reduced resistance from between 5% and 25%, higher top speed, better fuel economy and less noise on the aft decks.

Hull Vane also offer an active version of this system, namely their Dynamic Hull Vane®, said to raise performance levels even further. Developed in partnership with Naiad Dynamics, the system is governed by a Ride Control System using actuators to vary the angle of attack of the appendage, thereby increasing the damping and reducing the pitch motions by 30% to 45%.

For fully planning vessels operating in both recreational and professional markets, Foil Assist by Hull Vane® consists of a passive, mid-ship mounted wing under the bottom, which carries a significant portion of the displacement and therefore dampens the pitch excitation when sailing fast through waves.

By taking this load on the more deeply submerged wing, rather than on the running surface, means that waves have less influence, as the orbital motion of waves decreases with depth. Using the car analogy, Hull Vane® claims it feels more like active suspension has been added to the yacht creating a much smoother ride.

Lastly, Interceptors are active & intelligent trim tabs that offer speedy responses to reduce slamming, and, to a lesser extent, reduce roll, but their total effect is the least on offer from those other solutions we have discussed here. In some cases, Interceptors can be integrated with fins and rudders – the net effect promising stability across a wider range of on-water scenarios.

Fin Stabilisers
One of the most well-known, (but relatively young as stabiliser manufacturers go), is 112 year old Sleipner Motor, whose elegant and aesthetically pleasing Vector Fins caused quite a stir back in 2013, when the design scooped the coveted overall DAME Award for marine equipment design and innovation. The patented design, with its distinctive, concave face, curved sides and winglets on the bottom edge, proved that with proper hydrodynamic input, and a lot of R&D and real-time testing, a significant jump in roll reduction was achievable, compared to equivalent size ‘traditional’ flat-fin designs. Sleipner claim their Vector Fins can offer the same level of performance, or often that much better, yet from comparably smaller fin sizes. This means less drag and therefore less fuel consumption.

Reduced internals meant there was less power required for what was already a smaller fin size in the first place. And because everything was smaller, it gave installers and boat builders more scope to physically locate the fins in their most optimal position on the hull. In the event that a more compromised hull position was the only option available, less un-wanted ‘side-effects’ meant this design was also the most forgiving.

The secret is held mainly within the shape of the fins. The more up/down vertical motion re-directs the force direction, in such a way that more of it is put to good use. The concave face improves the net force angle, increasing the leverage arm around the boat’s rolling point which adds further to roll reduction.

And despite the reality of having two fins thrashing around underneath the hull, the up/down design (as opposed to a more horizontal side to side movement) was found to generate less of those inevitable side-effects of yaw and sway, which can create unpleasant motions and an unwanted ‘swimming effect’ in the water.

Proud of the impact his Vector Fins have made so far, Sleipner’s MD, Ronny Skauen, said: “The way we have seen boat usage change over the last years, and definitely this year with the Corona situation, people spend more time on their boats actually cruising, and many at slower speeds than before, both for fuel economy as well as general comfort.

“Taking into account also the other unique benefits our Vector fins have, with much less actual drag than flat fins because of their lifting/foiling functions, together with the focus on improved fuel efficiencies, we are seeing more and more naval architects ‘getting it’ now, resulting in Vector Fins being chosen by many high-profile vessels with a clear environmental and comfort efficiency focus.”

Another fin manufacturer we talked to was SKF Marine, formerly known as Blohm + Voss Industries, whose history with fins goes back 60 years. Dedicated not just to the engineering and development of fins, but other selected areas of a yacht’s engineering needs. In their time, SKF have had installed more than 700 fin systems within boats, but that has been across different marine sectors and not solely within the leisure marine market.

From their headquarters in Hamburg, SKF Marine offer their Retractable (Type Z) and Non-Retractable (Type FZ) hydraulic Fins in a range of sizes, both for zero speed and underway and a range that is more emphasised towards larger yachts and superyachts.

An electrically driven, non-retractable solution, Type EFZ, is currently under development and will be ready by the end of 2020 and it promises something special. The actuator is said to be silent, compact and easy to install, with stabilisers that can be locked into any position, even when switched off.

For equipment that is immersed in a salt¬water environment for most of its life, its build quality and operational reliability and consistency is key. In this respect, SKF’s Rotary Vane Drive, applicable to the Type Z and FZ models, is where German engineering really shines through.

The technology provides constant maximum torque throughout the operational range and the fins themselves operate through a large working angle of up to 120° from sweep to sweep, so performance can be optimised based upon prevailing conditions. Powered by SKF’s own hydraulic control unit, it has an ECO mode for efficiency and reduced fuel consumption and dual pumps give low noise and reduced vibration.
The owner, captain or crew can keep an eye on things via a bespoke graphic user interface with intuitive and interactive control functionality such as a preventive maintenance function, troubleshooting assistance, data logging and remote access option for assistance by SKF specialists at any time.

With a head-office in Cascina, near Pisa, Italy, and further dedicated offices in Norwich, UK and Fort Lauderdale, USA, CMC Marine are well placed to support a growing market share for fin stabilisers, and have recently strengthened their foothold as far as Australia, via their relationship with Stella Marine, in SE Queensland.

Best known for their Stabilis Electra range of fins for larger yachts and superyachts, the company can now address a far wider share of the market with their compact Waveless range.

A remarkably small interior footprint of just 9.5 inches means this new range is geared towards the 40ft to 70ft market yet benefitting from the same or very similar engineering components taken from the more established and proven Stabilis range. Powered-up using AC batteries, or with a 24volt DC option, the Waveless design is said to have more available torque due, in part, to a ‘flange on flange’ bolted together system, instead of using the more common through-shaft to connect the actuator with the fin.

CMC advise that installation of these smaller, lighter units, STAB 25 or STAB 30, for example, can even be considered by an experienced Do-It-Yourself minded owner, as long as he/she is familiar with the mounting and wiring-in of this kind of equipment, and in using glass-fibre. Once installed, the fins align themselves using in-built software.

Sounds like a very well thought out system to me, a sentiment underlined by UCINA in 2019, when CMC’s Waveless fin technology was chosen as one of the best designed accessories for boats in the same year.

Sam Crockford, Managing Director CMC Marine UK, told us: “A recent example of a new build that has installed Waveless is the new 32m X-Treme X-105 by Holterman Shipyard “Due for final delivery in 2021, we worked closely with Holterman to study the owner’s comfort requirements, which resulted in a 4x fin solution using a combination of 2x of the smaller STAB 25 at the rear and 2x larger STAB 40’s forward. These were combined with CMC’s unique Directa 120 electrical steering and propriety ARGO software that integrates the controls of the steering with the stabilisers to further enhance directional stability, reducing the risk of broaching and maintain higher course directionality.”

Small is beautiful
At the start of this report I referred to boats even in the 20ft size range who are now benefitting from stabilised hulls, and one company I had in mind when I wrote that was Seakeeper.

Based in Maryland, California, Seakeeper’s Gyro stabilisers encapsulate the market up to 85ft, but, of late, they’ve been placing more and more significance on the small boat market as well.

Up until recently, the Seakeeper 2 was their smallest model, available for boats in the 27ft to 35ft range, but the latest offering is the Seakeeper 1, targeted at the 23ft to 30ft size range. A package that so impressed the jury at this year’s Miami Boat Show that it was awarded winner of the Innovation Awards and voted one of the boating industry’s Top Products for 2020. With prices for the smallest Seakeeper unit under $15,000 excluding fitting, the outlay appears incredible value for money for the extra comfort they can bring. Seakeeper claim up to a max 95% roll reduction at zero speed but, at sea, when underway, it would be hard to place the same kind of certainty on this figure due to the potential variation in conditions.

Previous to my research, I had assumed that all gyros needed installation on the centreline of a boat, but oh how wrong I was. They can be installed virtually anywhere on board, above or below deck, with the smaller models powered by DC batteries, no additional generator power is required.

Another piece of trickery (the science of which will take far too long to explain here), is that vacuum encapsulation of the flywheel enables it to spin roughly three times faster and cuts weight down by roughly two-thirds. It halves the power requirement and ensures complete isolation from the harsh marine environment, safely protecting critical components such as the aforementioned flywheel, the motor and bearings.

You’re not always having to tweak or adjust these new systems either because an ‘all speeds / all conditions’ Active Control optimises torque and ensures the unit keeps working at its best, despite changeable wave patterns and different cruising speeds. With the new ‘baby’, the Seakeeper 1, the control panel is located on the unit itself, or you can choose to interface control within your already installed dashboard instruments.

Having installed something like 250 gyros to date, Nemo Marine Services, based in Port Rayon in the south of France, were Seakeeper’s first ‘Elite Dealer and Elite Service Centre’ outside of the US. They’ve installed and maintained gyros for the past two decades and for anyone interested in trying out the performance of a Seakeeper, the company’s ‘any-conditions’ sea-trial policy is available from the global dealer network.

Retrofitting stabiliser systems
For some manufacturers, retrofit accounts for at least half, if not more than half of annual turnover, for others it’s still very important, but less so financially.

On behalf of Nemo Marine Services, Charlie Mcvey, told us: “Retrofitting Seakeepers is our biggest market and our engineers will look at the available space on each boat on a case by case basis and work around that.
“The negative aspect is that, unfortunately, the value of some of the smaller boats we work on does not warrant a brand new Seakeeper. Our future goal is to reduce the price of the product and installation cost, so that it can be accessible to more people.”

Hull Vane Sales Director, Bruno Bouckaert, told us: “Of the 40 Hull Vanes built to date, about 50% have been for retrofits, while the other half were built for newbuilds. Retrofits are a great way to improve speed, range, noise output and seakeeping of an existing yacht or ship. When built from new, there are additional advantages, such as smaller main engines (and exhaust systems) to reach the required speed, and smaller fuel tanks (and less weight) to reach the required range. Improved hydrodynamics is a much smarter way to achieve the right speed and range than bigger engines and fuel tanks.”