The first four Rotor^®-tugs, RT INNOVATION and three sisters, started to work in the harbours of Bremerhaven and Rotterdam in January 1999. Though highly praised by specialist publications no further Rotor^®-tugs were ordered for quite a long time. Kooren Shipbuilding and Trading (KST), the company designing and marketing the concept, ordered the next two Rotor^®-tugs of type RT-60 with 60+ t bollard pull at ASL shipyard Pte Ltd (ASL) of Singapore in March 2004. The options for two more tugs of the same type were changed into firm orders shortly after. The four tugs were christened:

RT INNOVATION and her three sisters were examined thoroughly during the years following their commissioning. They were tested even in applications they were not designed for, as offshore and escort towage. The experiences made during these years influenced the further development of Rotor^®-tugs. KST worked out three new designs, 45tbp, 60tbp, and 75tbp tugs. The 60t design fulfilled best the requirements of the charterer of the first two tugs, Société Nouvelle de Remorquage du Havre (SNRH), for operation in Le Havre. The first two tugs, RT CLAIRE and RT STEPHANIE, were ordered at ASL of Singapore end of March 2004. The contract for detailed design was awarded to Vuyk Kenton, too of Singapore. Both tugs got christened end of July 2005. Redwise transferred both tugs to Rotterdam. RT STEPHANIE arrived on 1.11.2005 and RT CLAIRE on 15.12.2005 after executing some ship assisting in Singapore habour. RT ANTONIE and RT ZOE , which were ordered later, were handed over to their new owner KST on 8.03.2006. Redwise transferred them jointly to Europe. While taking bunkers in the Middle East RT ZOE was chartered to assist in the salvage of the HYUNDAI FORTUNE . She collided with the bow of the HYUNDAI FORTUNE on 3.04.2006, while still being run by a Redwise transfer crew. She was sent to Hamburg with a heavily damaged wheelhouse as deck load on the FAIRPARTNER. She arrived in Hamburg on 3.05.2006, got repaired by Blohm & Voss and went to work there. RT ANTONIE stayed in the Gulf of Aden to assist in the salvage of HYUNDAI FORTUNE, but only after the Redwise crew was replaced by a Kotug crew. She arrived in Bremerhaven in July 2006, were she is employed by Kotug since. In the following the RT ANTONIE and RT ZOE are described primarily as detail photographs exist. Divergent data of RT CLAIRE and RT STEPHANIE are added in parentheses.

General: The propulsion concept of the first Rotor^®-tugs remained unchanged. They are tractor tugs with two rudder propellers beneath the bow section and one beneath the stern instead of a skeg. All rudder propellers are protected by docking plates. The rudder propellers are Wartsilä/Lips type CS-200 (Niigata ZP-21). The controllable pitch propellers (fixed pitch propellers with clutch) are of 2,100mm (2,000mm) diameter and run in nozzles. Three Wartsilä 8L20 (Niigata 6L25) diesel engines with 1,340kW/ 1,821bhp (1,350kW/ 1,835bhp) at 1000rpm (750rpm) provide power to the rudder propellers. The tugs have a bollard pull foreward of 70t and astern of 68t and reach a free running speed of 12kts. The tank capacities are 128m³ diesel fuel, 42m³ fresh water, and 41m³ ballast water. The maximum range is 4,000nm using just one engine. Both tugs are equipped to FiFi1 standard (FiFi without standard) with two (one) Fishcon pumps of 1,200m³/h (1,500m³/h) each. They are coupled to the back end of the foreward engines. They provide water for the two (one) monitors and the drenching system with an output of 300m³/h.

Below main deck:

The aft rudder propeller is located in a separate compartment. In front of it is the engine room. It contains the three main engines, two Cummins diesel generator sets with 120kW output, and the fire fighting pumps. The main engines are placed as close as possible to the rudder propellers. Therefore the engines are not placed side by side anymore. In front of the engine room is the compartment for the foreward rudder propellers. Up front are two double-berth crew cabins separated by a sanitary space.

Main deck:

Superstructure:Two single-berth cabins with en-suite sanitary facilities for captain and chief are located at the front end on this deck. Galley, mess room, a toilet, and a utility/store room fitted with laundry area and space for the storage of oil skins and boots are arranged in the aft part of the deckhouse. All accomodation and the wheelhouse are fully air-conditioned. The engine uptakes are placed at both sides at the end of the deckhouse. Aft of the funnels are the CO2-room to port and a deck locker to starboard.

Afterdeck:The Plimsoll towing winch is hydraulically driven and has one drum and a warping head. The winch is located between the funnels and has a pulling power of 30t at up to 15m/min and a holding power of 150t. This winch, which is primarily used on a Rotor^®-tug, carries a 52mm steel wire, a 100mm synthetic fibre stretcher and a 48mm steel wire as pennant. A 65t towing hook is fixed to a bollard aft of the winch. A large towing fairlead is located on the afterdeck above the aft rudder propeller. The stern bulwark has an opening in which a small stern roller, L x Ø = 1,200 x 500mm, for anchor handling is mounted. From the inside it is hidden behind a flap.

Forecastle deck: It is raised approx. 1m above the afterdeck. The steps are at the end of the deckhouse. In front of the deckhouse an identical foreward towing winch is mounted. She carries a synthetic fibre rope at present. In front of the winch two electically driven Plimsoll anchor winches are placed.

Boat deck:

Foreward on starboard and port sides an inflatable liferaft for 6 persons each is mounted in a craddle. There is no boat. Aft of the funnels the two fire fighting monitors (one to starboard) are placed. A half high deck is placed in the middle. It contains the batterie room and store and carries the wheelhouse.

Wheelhouse deck:

The controls are fitted in two desks which are arranged longitudinal beside a sliding seat. Among them are separate Wartsilä (Niigata) control units for each rudder propellers and a master controller steering all propellers jointly. The navigational equipment contains magnet compass, gyro compass, autopilot, one radar, GPS, 2x echo sounder, and depth sounder. All but the three first-mentioned were supplied by Furuno. Communication equipment is to GMDSS-A2 standard and contains among others VHF, Navtex, Epirb, SART, Fax, and Intercom, supplied by a number of companies.

Navigation deck:

Operations:

RT STEPHANIE stayed most of the time in Le Havre though not allowed to work. Meanwhile the RT CLAIRE worked in Rotterdam. Both started to work in Le Havre in October 2006 after seven years of legal battles. RT ZOE and RT ANTONIE went to work immediately after arrival in Hamburg and Bremerhaven.

Specifications: