Gyrostabilisers reduce crew fatigue and vessel energy consumption, improving task execution and allowing offshore operators to use smaller vessels and increase annual operating days, writes VEEM marine sales manager Dan Fisher
Catamaran-hulled crew transfer vessels (CTVs) have proven successful at securing charters in the offshore wind sector. Several ship designers and operators are now looking to incorporate large, commercial-grade gyrostabilisers into newbuild or retrofit monohulls to work alongside these catamaran CTVs. The ability to make each demi-hull as long and slender as possible has meant catamarans have gone some way to mitigating pitch, while providing the deck area needed for a generous superstructure and limited deck cargo.
By taking the same principal and applying it to monohulls, a vessel with the same deck capacity and similar installed power will have a longer waterline length for even great pitch attenuation, with the added benefit of more useable space in the hull for additional passengers and cargo.
While some have questioned the effectiveness of gyrostabilisers at high speeds, sea trials conducted by VEEM have shown differently. Recent installations on CTVs in the Gulf of Mexico and survey vessels operating in the North Sea have shown that crew comfort and task execution have improved when in transit. While role reduction percentages may not be as great as those measured when the vessel is at rest, this is mainly attributable to the acquired hull damping that most vessels experience as they move up in speed.
Australia-based VEEM Ltd has been designing and manufacturing marine propulsion and stabilisation systems for recreational and commercial vessels since 1968. Based on extensive testing on vessels at various speeds, VEEM reports RMS roll reductions of over 60% at 19 knots.
“Recent installations have shown that crew comfort and task execution have improved when in transit”
In addition to comfort and operability, operators have reported that the performance of other vessel systems are also improved by gyrostabilisation and this may result in reduced energy consumption and less frequent maintenance for certain auxiliary equipment. For example, on dynamically positioned (DP) vessels, by reducing roll angles, operators can maintain more uniform horizontal thrust vectors and inhibit ventilation. This means that the thrusters are running less frequently and for shorter durations.
Depending on the characteristics of the vessel, roll-induced yaw and sway will also be reduced as roll angles are supressed, again putting less demand on thrusters and steering systems to maintain the vessel’s course or position.
In November, VEEM was conducting sea trials on a 34 m survey vessel fitted with two VG70SD gyrostabilisers. The survey team on board conducting the tests explained that the reduction in vessel roll yields straighter passes of mapped sea floor and improves the accuracy of data collected.
This in turn means that survey programmes can be conducted by vessels smaller than would otherwise be required to complete the task, when relying on size alone to minimise motions.
W2W and DP vessels
The cost savings of operating smaller vessels and increasing annual operating days with a more productive crew are not the only economic gains that can be realised by gyrostabilisers.
VEEM is currently involved with multiple projects that will use roll- and heave-compensating gangways on ‘walk-to-work’ (W2W) platforms. In both cases, providing a stable deck in the first instance not only provides crew and the personnel in transit with greater comfort, it also means gangways have smaller motions to overcome and can therefore be specified with smaller hydraulic systems and articulation limits. These projects, which are on DP2 vessels, are also aiming to quantify the improved station-keeping and reduced DP footprint, plus the beneficial effects on thruster demands and hence fuel efficiency by stabilising the vessel.
Reducing roll motions and vertical accelerations is just as applicable to heave-compensating cranes and overboarding equipment, which has the effect of either increasing capacity or providing the ability to utilise smaller and less power-demanding machinery.
“The reduction in vessel roll improves the accuracy of data”
Another development driving the need for more stable survey and military platforms is the increasing use of autonomous surface vehicles (ASVs) and autonomous underwater vehicles (AUVs). ASVs and AUVs can be used to form a wider array in conjunction with the parent vessel, or carry out independent missions on their own or in groups. The ability for one crewed vessel to cover a broader area has obvious cost-saving benefits and places a high value on the ability to launch and recover unmanned equipment reliability in a wider weather window.
The compounding effect of more charter days with greater safety, productivity and fewer costs is a compelling reason to adopt technology, such as marine gyrostabilisers, that make it possible.
Gyrostabilisers offer refinements away from in-water appendage drag, jerkiness, lower underwater noise, and risks associated with striking divers, sea life, floating objects (ice) and fixed structures with fins.
In addition, gyrostabilisers will never need drydocking for service or repairs and, in the case of all six of VEEM Marine’s models – ranging from the VG52SD generating 52kNms of angular momentum to the giant VG750SD that outputs 750kNms and has the potential to generate 1000kNm of roll counteracting torque – all are designed to be fully serviceable in the vessel.
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