machinery repair VSPs overhauled during one month docking
Gibdock has completed the renewal of two Voith Schneider Propeller (VSP) units on board the 57-tonne bollard pull harbour tug Siroco. The 2001-built 57-tonne bollard pull Boluda
group harbour tug Siroco arrived in Gibraltar in early June for a one-month docking that included the complete removal and overhaul of the two Voith Schneider Propeller (VSP) units on board. As soon as the vessel was drydocked, it was high-pressure jet washed and scraped to remove marine growth. Four plates were then cropped and two upright supports were removed to allow access for Gibdock engineers to remove the VSP blades. John Taylor, Gibdock production director, said: “This was a time consuming task and it took around two shifts to remove all 10 blades and transport them to the workshop for overhaul. This included disassembling, cleaning, calibrating and remounting the bearing assembly with new spare parts and all the blades had to be inspected and polished.”
Odessos Shiprepair Yard in Varna, Bulgaria, has completed a technically complex machinery overhaul on the ex-Lauritzen- owned Lapponian Reefer. Work consisted of dismantling, refitting and machining a new- generation hydraulically operated propeller hub and controllable pitch (CP) propeller tail shaft. The shaft was 8600mm in length and weighed 12,600kg. The hub weight was 10,600kg. The CP propeller had a diameter of 5,600mm and the weight of the blades was 10,800kg.
The vessel involved was a modern reefer vessel managed by Holy House Shipping of Sweden, a longstanding customer of Odessos. The scope of the work consisted of overhauling the CP propeller hub, and overhauling and renewing bearings and bushing. Work included:
Gibdock engineers then removed the two
rotor casings and transported them to the workshop. The main cover plate nuts were removed using a hydraulic torque multiplier, and all internal components, including pistons, gears, actuating rams and the thrust shaft were similarly transported to Gibdock’s mechanical workshop for overhaul. The VSPs’ rotor casings were then lowered from the vessel and, with the assistance of the yard’s shore cranes, were lifted from the dock bottom and transported to the workshop. Once the Voith Schneider units and rotor casings had been removed, the main deck fixtures were completely protected and the two openings were blanked off before blasting. Following the dismantling and inspection of
the rotor casing, the bearing flange assembly and protective ring was found to be extremely corroded. It was decided to fabricate and fit steel inserts to the two bearing flange assemblies. “Although this was unexpected extra work,
Next generation CP propeller hub repaired
• machining crank discs’ seats to new bearings size • guide bearing of cross-head, modification by machining and renewal of bronze liners • cross-head – machining the grooves and modification • crank discs – four pieces, machine and polish including pins • new sliding blocks – fabrication • fabrication of bearing crank discs, radial and axial (four sets x three pieces) • preliminary workshop tests of the complete system and pneumatic functional testing. Specialised workshop mechanical procedures were completed in 10 days, employing six to eight different machines simultaneously, in daily shifts, with an additional day for pre- assembly and pneumatic tests.
we incorporated a night shift to complete the repairs as soon as possible, in order not to affect the undocking date, which was crucial to the owners,” said Mr Taylor. The new inserts were machined to an external diameter of 1,285mm, internal diameter of 1,065mm and a 60mm thickness. These inserts were then fitted to the existing bearing flange assembly. While in the workshop, all the mechanical parts of the VSP units were cleaned and calibrated and the data recorded, and all the seals, packing and bushes were renewed, with Gibdock engineers working closely with service specialists from Voith Turbo Schneider. The reassembly of the VSP units in the workshop continued while a second full coat of paint was applied to the hull. Once the Voith Schneider systems were completely reassembled onboard and the access plates refitted and welded, a final full topcoat of silicone paint was applied to the tug’s hull and the vessel left for sea trials.
Other work on engine room machinery included extensive fuel oil tank cleaning and surveys, piping in the engine room, specific piping and connections renewed by stainless steel pipes, fitting ballast lines, pneumatic activation system of valves, a major overhaul of the Tenfjord steering gear, and testing of the 2, 000kW shaft generator. Work was also carried out on the cargo gear cranes, with the 36-ton crane jibs removed ashore for repair, renewals and modification of the pins and bushing at the jibs’ base, including functional and load tests.
Despite the unforeseen repairs to the bearing flange assemblies, the vessel was completed to the dry docking schedule of 30 days. No problems were encountered during the sea trials and the tug is now back in operation in Algeciras. MP
Inspecting a propeller hub cross-head
www.mpropulsion.com
Close up of the hydraulically operated propeller hub Marine Propulsion I February/March 2012 I 91
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