The roots of the shipping company Kotug (ex. Kooren) can be found in the second half of the 19. century. Towage services started in the beginning of the 20. Century on the dutch inland waterways and around Rotterdam. Kotug started ship assist services with second-hand tractor tugs with rudderpropellers in Rotterdam in 1987 and broke open the local towage monopole. These tugs are still owned by Kotug, the ZP Chandon and her sisters. In the early 1990s Kotug looked for ways to make this type of tugs better, based on the experiences with these tugs. The Rotor^®-tug was born. The tug was originally designed for Milford Haven, but the development of the tugs was continued, even when the tender for towing services for Milford Haven was not won. Therefore four Rotor^®-tugs were available, when Kotug started to offer ship assist services in Bremerhaven in the early days of 1999:

It was a long way from the first idea to the delivery of the first tug with many doubts about the feasibility of the design. The engineering development was carried out by the technical department of Kotug. Masters and crews were heard to bring in their experience. A large part of the design and drawing work was done by the engineering branch of the Padmos shipyard in Stellendam. To verify the calculations and to refine the design extensive tank tests were carried out at the dutch Maritime Research Institute (MARIN)in Wagingen. The first four tug were ordered in 1998. Two tugs, RT INNOVATION and RT PIONEER were built at Astilleros Balenciaga in Zumaia at the Bay of Biscay in Spain and delivered in January 1999. RT SPIRIT was delivered in February 1999 by Construcciones Navales P.Freire SA of Vigo in Spain. The same yard had delivered the shell of RT MAGIC to Padmos shipyard. After fitting out at Padmos the tug was delivered in April 1999. With three shipyards working simultanously to the same design differences are inevitable. So the four tugs are not totally identical.

General: A Rotor^®-tug is, simply put, a tractor tug with rudderpropellers, whose aft skeg was replaced by a third rudderpropeller. With this configuration all movements are possible as with a conventional tractor tug. Because of the third rudderpropeller, the Rotor^®-tug is more agile as there are higher thrust resultants available for all purposes. Comparing the turning circle through 360° within the ship's length of RT INNOVATION and JADE (URAG), tugs of comparable length and horsepower, shows this. RT INNOVATION turns in 24sec, JADE in 31sec. The Rotor^®-tug reaches athwartships a speed of 6kts and a bollard pull (thrust) of 95% of the maximum bollard. Voith-Schneider tractor tugs have an athwartships bollard pull (thrust) of approx. 60% of the maximum bollard pull, a tractor tug with rudderpropellers approx . 45 %, and an ASD-tug approx. 30%. The real value of these qualities can be assessed with difficulties only, as some publications represent Kotug advertising messages and additionally the special abilities and the high bollard pull of 78tonnes (t) always come as a package. As a Rotor^®-tug delivers almost the maximum bollard pull in every direction a repositioning of the tug in the direction of the towing connection is not necessary. This has to be done with normal tractor tugs when the full bollard pull is needed. The extreme manoevrability and high bollard pull help to work fast, efficiently and with less tugs especially in narrow waterway, e.g. locks. From my point of view the third rudderpropeller is only meaningful in extreme conditions. A Voith-Schneider tractor tug with 80t bollard pull has an athwartship bollard pull of almost 50t which is sufficient for 90% of the jobs according to Kotug. The Rotor^®-tugs reach these 50t with only two propulsions units working. A clear advantage is the smaller draught when comparing tractor tugs of equal horsepower. The RT CLAIRE, a new generation Rotor^®-tug of the RT 60 type with 70t bollard pull has a draught of 5.90m while BUGSIER 1 with 58t bollard pull has a draught of 6.40m. Even the three RT80r with 80t+ bollard pull, ordered by Bugsier towing company in April 2006, will have a draught of 5.95m only. Till today all Rotor^®-tugs were ordered by Kotug or Kooren Shipbuilding and Trading (KST) and sold or leased-out afterwards. Bugsier ordered the RT80r's because of their fast availability, their high bollard pull, the comparable small draught and the working Rotor^®-tug concept. The tugs of the RT INNOVATION class are driven by three Caterpillar type 3516 B DI-TA diesel engines with 2,100bhp (1,556kW) each at 1,600rpm. The three engines are mounted side by side in the engine room. The two outer engines drive the two Schottel SRP1212 FP beneath the bow, the middle engine the aft propulsion unit of the same type located beneath the stern. All three Schottel units are equipped with 5-blade, fixed pitch propellers of 2.15m diameter in Kort nozzles. The propellers were optimized for high bollard pull at the expense of the free running speed. Protective plates supported by struts are located in front of the bow propulsion units and behind the stern unit to protect them in case of grounding, and as docking aid. The tugs have a maximum speed of 12.5kts and a maximum bollard pull of 78t. This pull is reached with the foreward thrusters turned outside by 15° to minimize the interference between the three thrusters. With only two propulsion units working these figures are reduced to 9,5kts and 50t, sufficient for 90% of the jobs according to Kotug. The bunker capacities are 170m³ diesel fuel, 9m³ lubrication oil, 25m³ drinking water, and 113m³ ballast water.

Maindeck, forward:

On the forecastle deck a combined anchor- and towing winch type Ridderinkhof AMW-H-236 is mounted. The winch has a single drum carrying 200m x 56mm steel wire, 10m x 100mm synthetic rope as stretcher and 20m x 48mm steel wire pendant. The winch has a pulling power of 30t at a speed of 15m/min and a brake power of 200t. Additionally the winch has two chain lifters for stud-link anchor chains of 24mm diameter and two warping heads. The towing wire runs through a heavily reinforced fairlead in the bow bulwark. The deckhouse begins behind the winch. It contains among others two single-berth cabins, the galley, mess room, main switch room, battery room, and a store.

Maindeck, aft:

At the aft end of the deckhouse the towing deck begins. It is lowered approx. 1m in comparison to the forcastle deck. The deck carries the large hydraulically operated TW-H-300 Ridderinkhof towing winch. The winch has two drums and is of the waterfall type. The lower drum is parted into two drums, each carrying 200m x 56mm steel wire, 10m x 100mm synthetic rope as stretcher and 20m x 48mm steel wire pendant. The upper drum carries 650m x 56mm steel wire, 10m x 100mm synthetic rope as stretcher and 20m x 48mm steel wire pendant. The winch has a pulling power of 30t at a speed of 15m/min and a brake power of 200t. At the aft end of the winch a towing hook with a safe working load (s.w.l.) of 100t is mounted. It was supplied by Van de Graaf and is of the type GSH100. Between winch and stern bulwark a large towing fairlead with five posts is located.

Below maindeck:

The forward rudderpropeller compartment is located in front of the engine room. Two two-berth cabins are placed forward of the rudderpropeller compartment.

Deckhouse deck:

It is above the maindeck. The staircase, air-conditioning and ventilation room, and a store are located in the aft. In front of these rooms the master has his quarters. He has a sleeping room and a day room with office space. Two inflatable liferaft are mounted on craddles outside of the superstructure, one on each side. Companionways at the front of the superstructure lead downstairs to the bow winch and upstairs to the bridgedeck.

Bridgedeck:

Topdeck:

One searchlight and the magnetic compass are installed here. Additionally a bridge spans the gap between the tops of the funnels and carries the mast, a second searchlight and a fire fighting monitor delivering 600m³/h. The tugs are prepared for a later upgrade to FiFi1-standard.

Crew:

In harbour towing service the tugs are manned by a crew of three persons. In coastal towage the tugs can accommodate up to seven persons in three single-berth and two double-berth cabins.

Operations:

The tugs were designed with harbour towage in mind. So they are used primarily in ship assistance service in the ports of Rotterdam, Bremerhaven, and Hamburg. They proved themseves in coastal towage and offshore work too. The escorting abilities of the tugs was tested and approved in cooperation with the 130,00 dtw tanker NAVION SCANDIA in 2001. The large scale test approved the results of the tank test and showed that the Rotor^®-tugs are able to escort over the bow and the stern. Like an ASD-tug the tugs are not able to develop the high bollard pull of tractor tugs in indirect towing mode as the high hydro-dynamic forces produced by the skeg is missing because of the missing skeg.

four new, 3.30m shorter Rotor^®-tugs with 68t bollard pull were built and delivered in 2005. Four more tug with the same hull but 80+t bollard pull were ordered by Kooren Shipbuilding and Trading in Singapore in 2005. Three of them will be taken over by Bugsier towing company. Additional types are being developed. Among them is an escort tug of 37m length and 100t bollard pull which is designed in cooperation with Robert Allen Ltd. of Vancouver, Canada, after the escort tug designed by Kooren alone got too long with 43m.

Main dimensions: