DISCOVER Magazine #7

Damen’s FCS 2710: new and improved Fast Crew Supplier for windfarm industry

Published in category: Offshore Wind
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Source: Maritime Holland
Author: Bruno Bouckaert

Since the launch of their first Twin Axe FCS 2610 back in 2011, the Damen vessel has become a benchmark in crew transfer for the offshore wind industry. About 50 of these ships have been built, and while improvements were made along the way, it was time to design and build a new version, taking into account all the experience gained over the years and the evolved requirements from customers.

Client input

Damen Shipyards talked with their clients, in particular the majors (industry leaders) Vestas, Ørsted (Dong), Vattenfall and Siemens, to see what the users liked and what they didn’t like about the FCS 2610. This formed the basis to develop the FCS 2710, with a focus on cost-effective, comfortable and safe crew transportation. In spite of what her name might suggest, the FCS 2710 still fits within the 24 metres load line requirement.

The principle points of feedback on the FCS 2610 were that technicians / industrial personnel had to take too many stairs (to go to the seating area on the upper deck and to go to the transfer position on deck), that the deck was not a straight single-level flush deck, that the wet gear room was too small, and that the maneuverability and onboard comfort could be improved. Furthermore, the weights onboard increased over the years, which meant that the distance between the cross deck and the water became smaller, making the vessel more susceptible to cross-deck slamming in heavy seas.

Based on this feedback, Damen started the design with a clean slate. First of all, the foredeck was raised compared to the water and made continuous from fore to aft. It was chosen to move the seating position to the main deck, but ample forward and side views were maintained, which are essential in preventing seasickness. The working deck became a bit smaller at 90 square meters rather than 100, but as it is one continuous stepless area, it is much better useable.

Hull design

For the hull design, Damen maintained the basic principles which were so successful: two Sea Axe hulls for reduced vertical accelerations in heavy weather, and a roundshaped cross structure between the hulls to reduce cross-deck slamming. Compared to a standard (flat) catamaran cross deck, this tunnel reduces the impact of a cross-beam slam, but also there is additional reserve buoyancy in the tunnels which lifts the vessel when a high wave is passed.

The tunnel was raised by over a meter to increase the operability in heavy weather. The hull material remained aluminum, to keep the weight as low as possible for efficient running at high speed. For the hull shape of each hull, Damen compared a hard-chine hull with a round bilge hull for best performance, and chose the hard chine hull because of its lower resistance characteristics in the intended speed range (20-30 kn). A small hull extension was made aft to increase waterline length and buoyancy. At the same time, these low platforms ensure easy boarding in places where the quay is very low. Just like her predecessor, the FCS 2710 has course-keeping fins to avoid broaching in a following sea.

Catamaran

Catamarans are known to have a stiffer roll motion, and hence passengers are more often seasick on catamarans than on monohulls. Why are all turbine transfer vessels then catamarans? Wim Boerma, product manager of Damen explains: “We have both suitable monohulls and multihulls in our product range, but it’s our clients who specify that it has to be a catamaran. This is because of the most critical point in the transfer process: the landing at a turbine and the ship-to-ladder transfer of personnel. A catamaran is in this case a more stable platform, due to less rolling, making the step-over safer. A monohull can more easily loose contact with the landing posts due to its rolling motions.”

Engine rooms

The engine rooms received a complete make-over and moved to the aft of each hull. This gives Damen the possibility to offer the same vessel with five different propulsion configurations with minimal changes: fixed pitch propellers, controllable pitch propellers, Volvo IPS drives, Voith Linear Jets or waterjets.

In the standard propeller configuration, which is also the most efficient, the engines are coupled to V-drive gearboxes on the front, with the propeller shafts exiting aftwards under the engines. The V-drive gearboxes, which were developed by Reintjes especially for this purpose, also features a two-speed functionality of a second gearing, just like the previous FCS 2610. The additional gear allows for a better compromise between bollard pull at zero speed and propulsive efficiency at high speed. At 12 tons, the ‘bollard push’ is certainly sufficient. Customers who favour other propulsion systems, can opt for Volvo IPS drives, waterjets, or Voith Linear Jets.

The main engines are in a V-drive configuration
The main engines are in a V-drive configuration

Maneuverability

The maneuverability of the FCS 2710 was improved by installing larger bow thrusters (2x 64 kW instead of 2 x 50 kW). On the previous vessel, typically only the bow thruster blowing away from the ship would be used, as the flow of the other one would hit the opposite hull and become ineffective. The solution for this was to position each bow thruster with a downward angle towards the centerline. Because of this, the flow will pass below the other hull, ensuring that both bowthrusters can be used at the same time. Each bow thruster is driven hydraulically by a large PTO pump on the main engine’s gearbox, which ensures that maximum thruster power is already available when the main engines are only running stationary.

FCS 2710 under construction
The arched dome structure is placed higher for more clearance

Asymmetric deckhouse

Damen was the first to position the deckhouse at the aft, where ship motions are less, and this was of course retained for the new vessel. As more interior capacity was needed at main deck level, the deckhouse was extended forward, and to portside, where it occupies the port side walkway. The starboard walkway is wide enough to ensure that technicians can pass each other and the accommodation door.

The asymmetric weight was compensated by placing the crane on the starboard side, as well as some of the heavy technical components. To ensure each client can plan their accommodation space as they wish, there are no structural bulkheads on main deck level. The supporting pillars, which are required for constructional strength, can be moved within a certain range, so they can be in a bulkhead or in a position where they do not cause inconvenience. While some clients opt for maximum seating capacity, others prefer to have less seats (business class), a settee or even bunk beds useable by the technicians during transfer. The bulkheads and furniture are built of extremely lightweight aluminum honeycomb panels. Due to its larger size, the lightsip weight of the FCS 2710 is about 10 tons higher than that of the FCS 2610.

A Heila deck crane is used to load cargo
A Heila deck crane is used to load cargo

Accommodation

The increased space in the deckhouse and the relocation of the engine rooms aft has created more interior volume for crew cabins. There are three MLC-compliant cabins above the main deck, and one optional in each hull. There’s an extra two smaller cabins in the hulls which are not MLC-compliant, but which can be used for sleeping when in the harbor. These vessels are used both in windfarm construction projects, where work goes on 24/7, and in existing windfarm maintenance, where they are more like a bus service operating during the day.

HST Hudson Interior and crew cabins

The air-conditioning onboard is with aircooled AC units – as seen in buildings on land, but marinized- as these minimize the installation work and are easy to replace in case of a malfunction. In the seating room, there are large video screens, and the crew can use their own devices to connect to the Wifi network onboard, which gets its internet connection either through a satellite or 4G communication system, depending on the distance from shore. Charging these devices can easily be done with a socket and USB charger integrated in each seat.

 Interior FCS 2711 HST Hudson seating area
The seating area can be configured to the clients’ wishes

Just like the passenger seating compartment, the wheelhouse has excellent views all around. In addition, there is a topdeck window in the overhead, allowing the helmsman to look up to the turbine, from which craning operations often take place. Container fittings on deck are suitable for either two twenty-foot containers or four ten-foot containers. The FCS 2710 also has a fuel supply reel on the foredeck to resupply the generators in the wind turbines. There are several features built-in to ensure client upgrades are easy. For example, the working deck has an area free of systems to easily create a moon pool, and preparations for deck heating are installed. The engines are compliant with IMO Tier II, but the engine rooms offer sufficient space to accommodate Tier-III compliant aftertreatment systems. Each of the engines already has an exhaust silencer, and the exhaust is ejected between the hulls.

An overhead window in the wheelhouse roof ensures visibility of the turbine
An overhead window in the wheelhouse roof ensures visibility of the turbine

Regulations

To increase the capacity from 12 technicians to 26 technicians, the FCS 2710 was certified differently. It’s not anymore a cargo ship (which can always carry up to 12 passengers) like the original FCS 2610, but it complies with the Offshore Service Craft Regulations. This is an adaptation of the High Speed Craft code, of which variations are adopted by the British, Danish and German flag authorities, which differentiates industrial personnel (which have received basic safety training) from standard passengers. The more stringent regulations meant amongst others stricter damage stability requirements, a Failure Mode and Effect Analysis (FMEA), engine rooms insulated to A60 standard and the use of non-combustible material for the bulkheads. With this new certification, the 24-metres load line also became less important, and therefore, Damen now also offers a 34-metres version of the same vessel, with either additional accommodation or additional cargo deck space.

Hybrid propulsion

Damen has worked on a hybrid propulsion system, which it has installed on a monohull OPV, and which is also available on the FCS 2710 as an option. The goal of this is to be able to switch off the main engines when the vessel is sailing below 8 knots, for example in the waiting time between transfers. The idling speed of the FCS 2710 is about 8 knots, so it makes sense, for station keeping, to use the generator or even a battery bank at lower speeds. It’s a matter of looking at the operational profile of each vessel, as the additional weight of the hybrid system and possibly a battery bank will have a fuel consumption penalty at higher speeds, where the fuel consumption is much higher than at 8 knots.

HST Hudson

Seawork

Upon completion at the Damen shipyard in Antalya, Turkey, the HST Hudson sailed on her own keel to the UK. Damen introduced the vessel at the Seawork exhibition in Southampton, where the christening also took place. This first vessel was sold to High Speed Transfers, a new player in the market founded by several veterans of the industry. Damen has a second FCS 2710 under construction for stock. It is expected that in the windfarm industry, the new model will replace the FCS 2610, but it’s likely that the previous model will still be built for the oil&gas industry. The FCS 2610 quickly became the benchmark of the industry seven years ago. Damen has once again raised the bar with the FCS 2710, ensuring even more cost-effective windfarm maintenance and construction.

Dear reader, please note that position titles and job functions of Damen employees contributing to these articles is subject to change and description in this archive may, therefore become dated.

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