FOUR WAYS TO HELP STABILISE A SUPERYACHT
Written by Luke Wheeler
Last updated: 31/07/2019
If there’s one thing that can utterly ruin the high-class superyacht experience, it’s instability. Whether on a budget ferry carrying thousands of passengers across the sea, or a multi-million pound yacht taking a mere dozen guests to their next sunset destination, the sea will not consider a shipowner’s wealth or status when ruffling the vessels on its surface, the objects within it, and the people on them.
Thankfully, stabilisation technology in the marine industry has improved substantially over the last decade. Nowadays, stabilising a vessel is considered right from the moment pen touches paper. Hulls are being shaped and developed to combat the effects of active water, weight distribution is constantly being refined to achieve that walking-on-land feeling, and we’re spoilt for choice when it comes to marine stabilisers and the different types that can be fitted.
Now, we take a look at four primary methods currently used to stabilise the superyachts of our seas in 2019.
Adding ballast weight
In boating, ‘ballast’ is weight used for a specific purpose. It often refers to strategically placed added weight on board a vessel, typically within a ballast tank or system, to provide core levels of stability on the water.
Adding ballast helps maintain a deeper position in the water and lower the centre of gravity. Although this can be done with lead ballast, the same effect can also be achieved by the strategic use of ballast tanks loaded with water. Additionally, as other types of weight on board can also act as ballast, fuel becomes a consideration. On some boats, strategically filled fuel tanks can also act as convenient ballast.
Removing weight from the top
When we consider ballast, it’s worth considering its counter: weight above the waterline. Any weight above the waterline is going to be counter-productive to ballast, with weight at the very top of a vessel having the largest effect on instability. Not often a huge issue with motoryachts, but large sailing yachts with gigantic masts are a completely different challenge for stabilisation.
Having steel masts replaced by aluminium or composite masts is one way to drastically reduce the weight of an older sailing yacht, requiring less ballast and other stabilisation measures to counteract large masses above.
It comes as no surprise that a yacht’s hull severely affects its base stability: the larger and deeper the area beneath the water, the less affected by roll a boat will become. Whilst this is the case, it hasn’t meant that shipbuilders have begun adopting hulls that extend beneath the water for hundreds of metres — of course, all boats need to be able to fit in the relatively shallow waters of their marinas and other berthing locations.
Lengthening the hull or changing the boat’s type of stern are common adjustments in this area, and whilst often made for purposes other than stabilisation, this is a common intended secondary effect.
Of course, despite all the methods detailed above, further stabilisation measures are always desirable. Marine stabilisers are a class of product designed to be installed within a boat’s hull, with the sole purpose of reducing boat roll whilst entailing few other adjustments to the vessel.
Fin stabilisers, which quite literally look like fins sticking out the side of the hull beneath the waterline, work best underway. They work instantly and make it harder for a boat to roll, increasing stability. The size and configuration of the fins will be dependent on the boat’s size and its typical cruising speed, in order to provide its optimal level of stabilisation. As fin stabilisers are external appendages, they do create drag which lowers speed and fuel efficiency. At anchor, fin stabilisers typically do very little without being much larger and being specifically designed for at-anchor use. This is where gyro stabilisers come in.
Gyro stabilisers are a very different product. Mounted inside the hull and connected to electrical power to operate, these products effectively detect, and then correct boat roll using large amounts of torque generated by the stabiliser. This is all without external appendages like fin stabilisers, and functional just as well underway as it is at anchor.
A marine gyrostabiliser typically comprises of a spinning flywheel mounted in a gimbal frame that is fixed to a location on board. The flywheel is constrained in rotational motion that allows angular momentum of the spinning flywheel to combine with oscillation to generate large torques which vary with time to directly oppose the dynamic rolling motion caused by waves.
Like fins, there are downsides here too: gyros can be noisy when in operation which means their installation needs to be well considered. They also don’t work instantly—some can take up to an hour to fully ‘spin up’ once powered on. Still, these small drawbacks haven’t stopped many a large yacht from adopting a gyro-stabilisation system as the primary anti-roll measure on board.
You can read our guide on yacht stabilisers to learn more about the differences between fin and gyro stabilisation.
Thankfully, gone are the days where you’d need a stomach of steel to survive a few hours at sea. With the myriad of stabilisation techniques available to boatbuilders in this day and age, and the money typically spent on outfitting a yacht, you can bet that superyachts are some of the most planted boats on the water.