SC AMETHYST: An Innovative Gem for Safe and Quick Transport at Sea

On 6 March 2014, the small port of Maassluis was brimming with activity for the ceremonial naming ceremony of Sima Charters’ latest addition to the fleet: SC Amethyst. The company, established in 2000, operates a small fleet of fast vessels, transporting people and small equipment to ships in the anchorage outside the Port of Rotterdam and working offshore in dredging projects and wind farms. Since 2010, three vessels (SC Puma, SC Lynx and SC Cheetah) were purpose-built for these services. This class of vessels was called MPT 60, for multipurpose tender.

In the last few years, the demand for other services such as survey work, small supply work or crew transport to offshore wind farms, has increased, and Sima Charters’ CEO Ruud Lievaart set about creating a new generation of vessel to meet these demands, incorporating all the experience gained at sea over the years: the MPT 65. SC Amethyst is the first vessel of this series.

Gyro stabilizer

With an increasing amount of charter jobs further afield, the living space aboard has become very important, so for SC Amethyst, the crew quarters have received a significant upgrade. Three comfortable cabins are provided below the main deck, along with a two bathrooms and a spacious crew mess.

For the hull design, Lievaart is a strong proponent of the ride comfort provided by a fast monohull. Although the company also runs a catamaran for crew transport, his personal preference is for monohulls, as they do not suffer so much from the ‘jerky’ movements in heavy seas which cause seasickness. To further reduce the rolling motions, the design has included a Seakeeper gyro stabilizer from the very first sketches, as it has proven to be such an asset on Blue Whale, one of the other Sima Charter vessels. Not only does this improve the crew comfort during the time spent manoeuvring and waiting near a ship or wind turbine, it also increases the operational profile of the vessel. This is because the system is very effective at low speeds or standstill, and therefore improves the contact between the boat’s front fender and the windmill when push landing. Another advantage of the gyro stabilizers is the absence of underwater appendages. When comparing with appropriately sized fins, this results in an increase in top speed of one and a half knots.

Boat landing

A safe crew transfer at a wind turbine is all about creating enough friction between the boat’s fender and the wind turbine’s tube structure around the ladder. When a boat is rolling, this contact is constantly challenged, and hence more horsepower is needed to keep the bow stuck. As soon as the bow starts sliding up and down against the tubes, passage from boat to ladder is deemed unsafe, and transfer operations must be stopped. Lievaart estimates that the roll stabilizers add some 20 to 30 centimetres to the significant wave height under which operations are possible. SC Amethyst’s bollard pull is seven and a half tons, which should allow for operations in seas with a significant wave height up to two metres.

IPS propulsion

The most eye-catching novelty in SC Amethyst is the propulsion system. It is a constant source of debate in the industry which system best suits the conflicting requirements for wind farm maintenance: efficient high speed sailing, a high bollard pull for good fender contact and a high manoeuvrability at low speeds for safe approaches. The most widespread options are fixed propellers with dual-gear gearboxes, controllable pitch propellers and waterjets. With SC Amethyst, Sima Charters throws Volvo Penta’s IPS system into the mix. One of the advantages is the ability to generate sideways thrust, a big plus when the heading of the landing position does not line up with the incoming wind, waves and current. For a controlled slow-speed approach, the IPS system is equipped with trolling functionality. At her cruising speed of 21 knots, the fuel consumption of SC Amethyst is about 200 litres per hour, an exceptional figure according to Peter Bouma, chief naval architect at Sneek-based Vripack, responsible for the vessel’s design and engineering.

Plug and play

Volvo Penta’s IPS system has other advantages. For the builder, it is by far the easiest to install. The pod unit, flexibly mounted in the hull, includes the rudder installation and the exhaust installation (under water for less noise). This reduces the build time spent on auxiliary systems. With a complete length from the engine’s front side to the aftmost point of the pod of only 3,300 milimetres, the system is very compact and can be mounted very far aft, resulting in more useful hull space for accommodation.

The IPS 1050 units mounted on SC Amethyst are almost identical to the IPS 1200 used on motoryachts, but the power rating of the engines is reduced from 662 HP to 588 kW for more intensive commercial usage. With the pods mounted in the hull with flexible rings, and the engines mounted on soft mounts, the structural noise onboard is significantly reduced. Noise measurements in the main deck accommodation during sea trials showed exceptionally low readings: 62 dB(A) at 80 per cent power and 64 dB(A) at 100 per cent.

Hull design

SC Amethyst features a hard-chine planing hull with a sharp entry on the waterline and with sprayrails transitioning into relatively wide chine flats in the aft sections. To optimise the running trim at varying speeds, interceptors from Humphree are mounted on the stern. To achieve her top speed of 28 knots, while accommodating the 1,400 kilogramme gyro stabilizer, SC Amethyst was put on a strict diet during the design and build phase.

The hull has transverse frames every 40 centimetres, resulting in a light and strong structure. Weight was also saved by using cored lightweight panels in the interior. The side windows of the superstructure are made of Lexan instead of glass, saving another 300 kilogrammes. Another 200 kilogrammes were saved by using Li-Ion batteries from Mastervolt instead of more traditional batteries. In spite of all the weight saving, the interior of SC Amethyst looks sturdy and is finished to a very high standard. The modern casual styling will undoubtedly also improve the crew’s wellbeing, as well as the passengers’ comfort. Each of the twelve passenger seats has seatbelts and armrests on either side.

The wheelhouse has four screens displaying radar, charts, CCTV and the alarm and monitoring system. The particularly narrow window mullions result in an excellent view all around the vessel. The propulsion can be controlled by a joystick for easy manoeuvring, and in addition to the main steering position, extra control positions are provided at the entrance of the superstructure (used during cargo operations) and at the man-overboard-recovery system.

Outfitting

That same high standard is visible on the outside, with polished stainless steel handrails, closed bulwarks and non-skid composite deck coverings. The handrails are required for windfarm jobs, but they are removed for pilot and chartering work. In that case, holders can be mounted in the handrail sockets to hold the ball fenders, thus avoiding the fender lines on the side decks. Both the inboard handrail and the T-rails for the safety lines are electrically heated, eliminating ice formation in wintertime. The aft deck is completely surrounded by a high closed bulwark, providing a sheltered position for deck cargo (which can include a 10-foot container). At the stern is a man-overboard recovery system, built by Ship Install, to recover persons from the sea. During Sima Charters’ safety drills several years ago, it became apparent that it can be almost impossible to haul an unconscious person onboard. Since then, Sima Charters has fitted a hydraulic tilting platform on the stern of all its vessels. The fendering on SC Amethyst, supplied by Fender Innovations, is lightweight and custom-built. The side fenders have recesses shaped to create space for a ship’s pilot ladder. At the bow there is an experimental shock-absorbing fender with a special coating to increase the friction with the mooring pillars of a wind turbine.

Construction

The hull was built by Frisian Shipbuilding (Lemmer), and outfitting took place near the interior builder Altena shipyards in Raamsdonkveer, with Ship Install (Heusden) taking care of technical installation and project management. Along with the gyro stabilizer, the technical space forward of the engine room houses a 700 millimetre diameter moonpool. Currently the moonpool holds a dummy to avoid abrupt changes in the hull lines, but hydrographic survey equipment can easily be mounted in the moonpool without drydocking.

SC Amethyst is built under Lloyd’s Register class rules for Special Service Craft, and – due to reduced manning requirements – sails under the flag of the UK. She is certified for operations up to 150 nautical miles from the coast. The IPS units are designed to sheer off in the case of strong impact with an underwater obstacle, and will leave the hull intact and watertight. Sima Charters has two spare IPS units in stock, so a quick replacement of a unit is always possible. Only time will tell whether this was a necessary investment.

Conclusion

With the design of SC Amethyst, Lievaart from Sima Charters decided to go a different route than most. Convinced of the superior seakeeping of a well-designed planing monohull, and based upon his experience with previous pilot vessels, he added a gyroscopic stabilizing system and Volvo’s IPS drives for propulsion to create a unique vessel that will certainly do well as a charter vessel, pilot vessel and wind farm maintenance vessel. The vessel is prepared for a variety of tasks. For example, the hydraulics are already in place if an A-frame has to be installed over the stern instead of the man-overboard recovery system.

Bruno Bouckaert