Commercial Rib Charter (CRC) operates the largest fleet of commercial cabin RIBs in Europe, with more than 30 vessels ranging from 4m to 20m, alongside a growing selection of catamarans deployed across wind farm construction and maintenance, survey and ROV projects, nearshore cable landings, and guard and safety boat charters. In a typical year, these vessels accumulate 1,000 to 2,000 hours of machinery time, frequently running 24/7 through peak summer periods. During the quieter winter months, CRC commissioned MIT Group to carry out the full strip-down and overhaul of five Twin Disc Quickshift gearboxes from its crew transfer fleet, completed from MIT’s southern service centre in Queenborough.

Project Specifications

Parameter	Details
Client	Commercial Rib Charter (CRC)
Named Vessel	CRC Vulcan
Vessel Type	16m Crew Transfer Vessel (CTV)
Engines (CRC Vulcan)	2x Scania DI16 42M
Total Power	2x 650 hp @ 2,100 rpm
Marine Gearboxes	2x Twin Disc MGX-5135SC (CRC Vulcan) / 2x Twin Disc MGX-509SC (second crew transfer catamaran)
Gear Ratio	1.28:1
Propulsion System	MJP Waterjets
Top Speed	25 knots
Dimensions	16m LOA, 6.3m Beam, 0.9m Draft
Total Gearboxes Overhauled	5 Twin Disc Quickshift units
Service Location	MIT Group Southern Service Centre, Queenborough
Primary Scope	Full strip-down, inspection, service reporting, parts sourcing, refit, testing, and painting

Pre-Overhaul Assessment and Maintenance Planning

CRC Vulcan entered service with CRC in 2020 as a shallow-draft crew transfer and survey platform, equipped with a survey pole and an A-frame for ROV project support. By the time of this refit, both Twin Disc MGX-5135SC gearboxes had accumulated in excess of 10,000 hours coupled to the Scania DI16 engines. A second catamaran in the fleet, fitted with Twin Disc MGX-509SC units coupled to Iveco Cursor 9 inboard diesels, had reached 5,000 hours. A fifth Quickshift unit from within the fleet completed the programme. CRC coordinated with MIT Group through a commercial vessel refit survey to schedule all five units across the winter period, consolidating the work into a single planned programme to ensure faultless reliability ahead of the forthcoming operational season.

Workshop Strip-Down, Inspection and Overhaul

Each unit was fully dismantled at Queenborough, with all findings documented in a formal service report issued to CRC’s operations team as the basis for parts authorisation and scope confirmation.

Twin Disc MGX-5135SC Units (CRC Vulcan, 10,000+ Hours)

Both high-hour units were found to be in a surprisingly good internal condition relative to their service hours, with clutch plates remaining within acceptable parameters. One unit required drive coupling and snap ring repair, captured in the service report and rectified before return to service.

Twin Disc MGX-509SC Units (Second Catamaran, 5,000 Hours)3

These units were overhauled on a proactive renewal basis, with the following components replaced regardless of measured condition:

Drive plates
Coupling rubbers
All internal seals

All five gearboxes were reassembled to Twin Disc specification, tested, painted, and prepared for refit.

Return to Service and Fleet Outcome

With all five units overhauled and finished, the gearboxes were returned and refitted to the respective vessels. Where dry dock management forms part of a wider refit programme, MIT Group co-ordinates these activities as an integrated scope. The programme extended the operational service life of all five units and provided CRC’s operations team with a full service record for each gearbox, supporting ongoing fleet maintenance planning and certification requirements.

“We have been very impressed with MIT’s quality of work with these gearbox overhauls and believe we have extended their working lives for many years with this investment. MIT’s professionalism and expertise are unrivalled in the UK, and we look forward to working with them again.”

Jack Weller, Operations Manager, Commercial Rib Charters

Plan Your Next Gearbox Overhaul with MIT Group

MIT Group manages multi-unit gearbox overhaul programmes for commercial RIB charter operators and crew transfer fleets, delivering full strip, service reporting, parts supply, refit, test, and finish within planned maintenance windows. Contact our Marine Repair Team to arrange a technical consultation or to plan your next scheduled overhaul.

Twin Disc Quickshift Gearbox Overhaul for Commercial RIB Charter’s Crew Transfer Fleet