Welcome to the first in a series of tech blogs where we will delve into the various intricacies and deliberations our technical team have gone through in order to create the most advanced, efficient and stable explorer vessel in its class.
Here, we examine the thought processes that went into the selection of the stabilising system.
For intrepid, long range cruising types, exceptionally high levels of comfort and onboard safety are not luxuries, they are prerequisites. So Arksen’s goal is straightforward; to deliver what it anticipates will be amongst the most effectively stabilised vessels on the planet. In challenging conditions, either at rest or underway, good stabilising systems can profoundly improve comfort onboard. They also significantly increase crew safety and confidence by markedly reducing vessel motions, allowing the crew to move around and control their boat more easily. Unsurprisingly, seasickness becomes far less of an issue too, but the frequently unrecognised benefit is improved fuel consumption; vessels that lurch around in messy seas will consume more fuel than their unwavering, well stabilised counterparts.
Early on, though, it became apparent that no one stabilising system provided all the benefits that the Arksen team was looking for. The upshot is that the first Arksen 85 will be fitted with three complimentary stabilising systems: fins, a gyro stabiliser, and flopper-stoppers.
All our hands-on testing showed that gyros are unbeatable at providing stability at rest. This is because they are extremely fast acting (to all intents instantaneous) and they are capable of developing their full anti-rolling-torque almost immediately, so they can catch and correct smaller rolling motions almost before the crew feel them starting. Fins operate very differently, swishing back and forth to push and pull water around to correct for roll when a boat is anchored. They do make a substantive difference to stability at rest, but all the testing we conducted suggested that however large they might be, flapping fins were unlikely to be able to match a gyro’s effectiveness in this department. So for the Arksen team, a gyro was a must.
Gyros boast other benefits too. Arksen’s gyro is installed in the sound-proofed engineroom, so it cannot be damaged by semi-submerged objects like logs and containers and ice floes, or by grounding, nor can it get tangled up in fishing nets. Arksen skippers will have no need to turn their gyro off when their crew go swimming nearby, or when vulnerable marine life is proximate, as they might be inclined to do with big fins.
However, as boat speed increases, the effectiveness of a gyro begins to fall away, whereas the stabilising power of fins increases progressively; climb from 5 knots to 10 knots and the fins will be capable of developing four times the stabilising force. At the point where you might need the most control, say, surfing down a big ocean wave at 20 knots, the fins could potentially provide sixteen times their 5-knot stabilising force if required. Also, as long as a vessel is moving forward, fins can provide a continuous, uninterrupted hydrodynamic force to correct for wind induced heel or a persistent wave induced list, and no gyro is able to do that. All told, if you want to stay largely upright, travelling at speed in virtually any sea conditions, fins are the only realistic solution. In our opinion, these two key benefits are essential for an ocean crossing vessel. So for the Arksen team, fins were also a must.
Redundancy and backup are cornerstones of Arksen’s philosophical approach to design. Flopper-stoppers are a long established manually deployed stabilising system that are perceived by many as antiquated and superfluous. However, an unbreakable, low cost, zero-power mechanical system that can be used variously as an emergency back-up, as a supplement to the other two primary systems, and as a completely soundless option in silent anchorages seemed like an excellent idea to us, old fashioned or not. So for the Arksen team, flopper-stoppers were a must too.
There are several extremely good electric and hydraulic fin systems to choose from, and they all offer the benefit of the instant start-up and shut down that gyros cannot emulate (it can take an hour for a gyro to spool up to operational speed) a distinct advantage when you first arrive at a quiet anchorage and want instant stabilising comfort. So why did Arksen opt for electric rather than hydraulic fins?
In short, unbeatable functionality. Arksen’s all-electric fins can be instructed to swivel through 180 degrees. At anchor, this allows the fins to gently pull the boat back against the anchor chain, eliminating the forward-paddling effect that is the usual consequence of fins flapping around. That stops the vessel climbing forward over its anchor, and notwithstanding disobliging tides, it should also help to keep the bow pointing into the wind and waves, providing a virtuous circle of reduced rolling that assists both the fins and the gyro. Crucially, the Arksen team decided not to reduce the size of the fins to allow for the gyro’s potential contribution. To provide the very best stability at rest, the fins are sized as if there were no gyro.
At night, the owner can choose one of three fin damping modes; full, medium, or soft, which reduces the degree of stabilisation in return for reduced current draw. In conjunction, the owner can dial in a roll angle trigger-point which allows the boat to roll a little more (up to 4 degrees) before it triggers the fins. Both these benefits go hand in hand with Arksen’s philosophy of reducing energy consumption and its consequent environmental impact. This functionality also has the potential to significantly increase the time that the vessel can operate silently, in zero-emission, battery-only mode.
Unlike a gyro, fins are inevitably exposed to potential impact and damage underway, with the possible knock-on effect of damage to the surrounding hull structure. To tackle this issue, unlike most hydraulic through-hull shaft mounted fins, Arksen’s carbon fibre fins sport a large circular flange mounting which is designed to shear off in the event of a serious impact, leaving the hull intact. In the unlikely event of loosing a fin, they can be rapidly replaced; even underwater, because they possess neutral buoyancy.
The vast majority of boats rely on a single type of stabilising system. And most of the time that solitary system will prove adequate for the conditions those boats are likely to encounter. But most are unlikely to encounter the conditions that many Arksen owners will be faced with, so a different approach was needed. All told, the Arksen team sees fins and gyros and flopper-stoppers as the perfect partners for optimum all-round stabilisation.
