Artemis: Hellenic Goddess Assumes Role in the Van Oord Fleet

After having successfully finished the three-week sea trails and the contractual docking, IHC Merwede delivered CSD (cutter suction dredger) Artemis on Wednesday 3 April 2013 to her new owner, Van Oord. This is an impressive achievement as it is eight weeks before the agreed delivery date. The contract between Van Oord and IHC Dredgers, part of IHC Merwede, for the design, construction and delivery of the vessel was signed on 20 December 2010. The keel was laid on 22 December 2010; at that time her older sister Athena was nearing completion.

In mid-April 2013 Artemis commenced her first assignment in France. Commissioned by the ‘Grand Port Maritime de la Rochelle’ Artemis will deepen the harbour basin and dredge a trench in the entrance channel to the port. The material to be dredged consists of approximately 500,000 m3 of very hard rock and clay.

The Artemis is a self-propelled cutter suction dredger built specifically for dredging hard materials and, together with Athena, is amongst the largest self-propelled CSDs built in the Netherlands. The name ‘Artemis’ follows Van Oord’s tradition of naming its cutter suction dredgers after persons from the Greek mythology. In the classical period of Greek mythology, Artemis was often described as the daughter of Zeus and Leto, and the twin sister of Apollo. She was the Hellenic goddess of the hunt.

IHC Dredgers and Van Oord

Van Oord is one of the leading international contractors specialised in dredging, marine engineering and offshore projects (oil, gas and wind energy). The company is a Dutch-based, independent family owned business. With the signing of the contract for Van Oord’s second CSD, Pieter van Oord, CEO, stated that if you only have one vessel in the branch you just don’t count. So, in line with the saying ‘in for a penny, in for a pound’, Van Oord decided that Athena needed a sister. Van Oord continues: ”By investing in two self-propelled cutter suction dredgers and two large backhoe dredgers, we have strengthened our position in the dredging market significantly. This is in line with our strategy to have a very strong position in all segments of the dredging market.”

Obviously, when considering building another CSD, Van Oord preferred using the design of Athena, as building a sister vessel would have several advantages: proven and successful design, relatively short building time, optimised building sequence and reduced spare parts. The change of the critical path, as a result of the optimised building sequence, however provided new challenges in the scheduling, as shorter delivery times for components were required.

Flexible and ergonomie

Artemis is a strong and robust ship in which saving costs in the operational process is of utmost importance. The ergonomie design is characterised by flexibility in more than one aspect, as can be seen below. One exceptional feature is its hydraulically buffered spud carriage with a net stroke of approximately ten metres. The spud pole carriage is allowed some movement on its four hydraulic positioning cylinders (two at the top and two at the bottom). During dredging activities the forces on it with respect to the dredging depth are continuously monitored, giving accurate information on and control over the bending moments in the spud. The combination of above features enable the crew to continue to work even during challenging weather conditions.

To reduce noise and vibration in the accommodation, the entire superstructure is mounted on pneumatic dampers supplied by Loggers. When in transit, the pneumatic bellows of the dampers will be empty and the superstructure rests on and is secured to the steel deck. While dredging, air is injected into the bellows and the superstructure ‘floats free’ above the main deck. The normally problematic transmission of vibrations of a cutter head cutting into a rocky bottom is thus eliminated. As a result, Artemis can have crew ’round the clock’ on board, working in shifts.

Most of the wheelhouse windows are full height to ensure optimum visibility. As the barge-loading system does not allow for actual bridge wings, this is compensated by a CCTV system with four extra (Bureau Veritas class certified) cameras, focused on all relevant locations on board. Visibility is also improved by using a sophisticated triple radar configuration: the output of one radar on top of the wheelhouse and two radars above the bow are combined into one digital radar image on the bridge. This configuration provides all relevant information required for navigation and dredging activities.

Dredging characteristics

Artemis is designed for cutting through heavy soil and rock at water depths of 25 metres. It is equipped with two inboard dredge pumps and one submerged dredge pump on the cutter ladder, 5,000 kW each. The cutter is mounted on the cutter ladder and is driven by two electric motors, identical to the propulsion motors, through a heavy duty gearbox with torque monitoring. The cutter pumps and winches are all driven by electric motors, powered and controlled through water-cooled variable frequency drives.

The dredging is performed in a swinging motion, where the cutter ladder is pulled to port or starboard by the side winches with cables attached to anchors. The centre of rotation is the main spud, which is mounted in a carriage to allow for forward dredge movement after each swing. When the end of the spud carrier track is reached, the auxiliary spud is lowered for a short period of time, to allow the main spud carrier to be brought back to the other end of the track.

The dredged spoil can either be pumped ashore, through a 1,000 millimetre diameter pipe, or discharged into a barge. The vessel is equipped with an sophisticated barge-loading system with adjustable outflow at multiple locations and an articulated supply tube, employing hinged supports and four cylinders per side. There are three loading chutes and two valves in the discharge tube which can fill barges moored alongside better, distributing the load over the full surface. While the spoil comes out of the discharge pipe, dedicated barge mooring winches slowly move the barge alongside the CSD, ensuring equal filling of the entire barge hopper.

Artemis is equipped with a condition monitoring system (CMS). The CMS keeps a close eye on a large number of parameters, including fluid pressures, temperatures and vibration levels in bearings, and alerts the engineers to any anomalies allowing for a timely intervention and efficient replacement of parts. Durability is further ensured by using hard-wear resistant liners (Mohard) in the dredge pipe, plastic gratings on deck and GRE-piping for the seawater flushing system, which flows continuously to keep sand out of all equipment, such as gate valves, that may be effected by the dredged material.

Cutter manipulator 3

Replacing teeth on a cutter head is a regular event on a cutter dredger. While traditionally this would mean a time consuming interruption in production, this procedure has been streamlined on Artemis. The vessel has multiple cutters on board and is provided with a storage platform on both sides of the ladder gantry. A custom-built cutter-changing device can quickly remove worn-out cutters from the cutter ladder and place them vertically on one of the side platforms. It then repositions a reconditioned or new cutter from the other platform and places it back onto the cutter ladder. While the dredging continues, the worn-out cutter crown can be moved to the workshop by crane where the teeth can be replaced or reconditioned.

Fully diesel-electric engine room

The use of a fully diesel-electric system led to a more optimal lay-out of the vessel and allows for a more precise control over the pump speeds through variable frequency drives, with only a marginal loss in fuel efficiency. The engine room comprises three main diesel generators that each supply 24,658 kW to a high-voltage network of 6.6 kV. Each main generator set includes an alternator of 8,125 kVA. The low voltage (400 V) switchboard is also supplied from the same alternators by means of transformers. Alternatively, it can be fed from the auxiliary or emergency alternator, rated at 1,250 kVA each, or through the shore supply.

As a result of the recess for the cutter ladder, the aft ship has two ‘bodies’. Each houses an electrical propulsion motor, coupled to a classical horizontal shaft installation. These electric motors are also powered and controlled by water-cooled variable frequency drives. For steering, Artemis has two independently controlled propeller nozzles instead of conventional rudders. The engine control room is also linked to the CCTV system,

In for a penny, in for a pound, as they say

expanding possibilities for reading and displaying all relevant engine (room) data.

Wheelhouse

The wheelhouse navigation console is mounted off-centre facing forward to allow a better view from the dredging console on the spud carrier. The console is provided with all the required navigation and communication equipment, a custom-built radar system (composing a single display from the input of three scanners) and a CCTV system to provide good visibility for the operators on the bridge at all times.

The dredging console, mounted on centreline facing aft, consists of five displays mounted above the windows and three below. Whilst the console is split, the view through the windows is excellent. All relevant data (from main engines, auxiliaries and hydraulics, IHC System Automation, AMS) is available on the musbus system by means of a ‘layer 3’ switch. The musbus system allows multiple users to access information on all the various systems depending on the location of access, furthermore each user can display only what he/she requires.

Artemis versus Athena

As stated above Artemis is the sister of the Athena, which was delivered in 2011. Drawing on the experience gained with Athena, Artemis incorporates a number of upgrades for regulatory compliance and recent developments in technology, efficiency and comfort. The first difference to its sister can be found on the bridge and mainly comprises of an upgrade of the dredging software, developed in a joint effort of IHC Merwede and Van Oord. As no other industry evolves as rapidly as the automation and technology branch, it should not come as a surprise that we can also find several new/ upgraded components on the bridge in the ship’s electronic systems.

The second alteration is a change of ceiling material at several locations. The Athena proved to be so quiet, that reverberation of human voices became dominant. For this purpose the ceiling in the mess room, bar and offices were changed to perforated ceilings enhancing noise absorption.

The third issue is the optimisation and repositioning of the masts, navigation lights and radar scanners. The forward mast now is hinged to provide more space for maintenance to and exchanging of the hydraulic cylinders of the spud carriage. And the last, less noticeable, change is an optimisation of the propellers.

Green passport 

The Artemis can be considered environment friendly, as oil and grease lubrication emission into the environment is virtually eliminated. Considerable effort was put into designing mechanical components for the dredging system that can function without (or with reduced) lubrication. Another significant environmental innovation is found in the cutter ladder, as all cutter shaft bearings are fully water-lubricated. Any grease or lubrication needed, is standardised and provided automatically by an ingenious dosing system which reduces grease consumption by 60% to 70%.

The CSD is certified for dredging over 15 miles from shore with a significant wave height up to 2.5 metres. Furthermore, Bureau Veritas granted the vessel the Clean Ship notation, because of its ability to control and limit the emission of polluting substances, ranging from garbage to sewage and oily water.

With this vessel, IHC Merwede went one step further and delivered the vessel with a ‘Green Passport’. A ‘Green Passport’ is a document listing all the potentially hazardous materials on board. This document will stay with the ship throughout its lifespan and up until it is decommissioned. Having such a document ensures that no workers on board the vessel or at a shipyard will be exposed to such dangers as asbestos, PCBs, TBTs and others.

Tom Oomkens