Splash247 names that ship MSC Ikaria VI, about 5,576 teu. VesselFinder lists IMO 9261449 under that painted name. Press prints the tug as 286 tonnes. VesselFinder lists TNS Catcher as IMO 9412153, 444 gt. Those two figures are not merged.

Busan Coast Guard, via Seoul Economic Daily and Splash247, said two tugs were pulling at the bow and one was pushing at the stern. TNS Catcher was on the starboard bow, turning to starboard, when it rolled to port. Investigators treat towline tension during the turn as the leading line. A collision with the containership has been ruled out. Herald Business reported the boxship’s AIS as Not Under Command that day. PortNews said the call-out followed an engine failure.

Eight were aboard: six South Koreans and two Indonesians. One Indonesian was rescued. One South Korean was recovered unconscious and died in hospital. Six remain missing. The hull sank and was found in about 87 m of water. Search expanded to 66 km by 40 km with 24 vessels and seven aircraft. Underwater visibility at the wreck was about 30 cm.

Why tugs matter

A large ship at slow speed in confined water does not steer or stop on the rudder alone. The tug supplies the missing force: push on the shoulder, pull on a line, hold a disabled hull off a bank. When a containership is Not Under Command, the tug is the only control that can still be applied from outside the engine.

The price of that force is the line. If the attended ship’s heading, speed or the tug’s heading change faster than the tug master can slack or slew, the towline can come up short across the tug’s beam. That heels the tug toward the line. If the heel goes past the point where the deck edge takes water, the tug can capsize in seconds. That is why a 286-tonne tug can be lost under a 66,000-gt boxship without a collision. The line did the work, then it did the damage.

Harbour tugs also keep the port open. Without them, an engine failure off Oryukdo is a drift toward the rocks, not a controlled return to Busan.

Types of tugs and how they push

Three common layouts sit under the same job.

Conventional. One or two fixed shafts, propeller and rudder. Good at sea and for long ocean tows. Ahead bollard pull is high; astern pull drops. The towing point is usually aft. That geometry is why conventional tugs are more exposed to being girded when the attended ship overruns the line.

Azimuth stern drive (ASD). Two Z-drive units under the stern. Each unit is a propeller in a nozzle that can rotate 360 degrees about a vertical axis. The tug can thrust in any horizontal direction, spin on the spot, or work as a reverse tractor over the bow winch. Most modern harbour fleets are ASD. The units sit where a conventional twin-screw would sit; the difference is that there is no separate rudder.

Tractor (Voith or azimuth). Propulsion is forward, about 0.3 of length from the bow. The towing point is aft. A Voith Schneider unit is a rotating disc with vertical blades whose pitch can be changed while the disc turns, so thrust direction changes without waiting for a shaft to reverse. An azimuth tractor uses Z-drives in the same forward position, with a large skeg aft. Response is fast. The trade is draught and complexity.

PortNews, citing TNS Ocean Towing fleet data, gives TNS Catcher 3,600 bhp and 49.1 tonnes bollard pull. That is harbour-assist power, not an ocean-going salvage tug. The pack does not print whether Catcher was ASD, tractor or conventional.

Established

• TNS Catcher capsized ~13:29 on 2 Sep about 9 km from Oryukdo while assisting a 66,332-gt Liberia-flag containership (Busan CG via named press).
• One dead, one rescued, six missing. Wreck ~87 m.
• CG: no collision; towline tension during a starboard turn is the working line of inquiry.

Not established

• Official CG PDF in this pack.
• Merged GT for the tug (286 t press vs 444 gt VesselFinder).
• Propulsion type of TNS Catcher.
• Exact wreck name (Songjeong vs Daebyeon).