26 Apr 2022

RV ‘Kaharoa’ survey requires significant work on propulsion and steering systems

In early March, NIWA’s 28 metre research vessel, 'Kaharoa' underwent an extensive survey and maintenance schedule over a 5-week period on the Port Nelson slipway.  As part of the survey work, both the propulsion shaft and the rudder system were required to be pulled for inspection.

The top end of the steering gear was disassembled - including the steering hydraulic rams, tiller and associated components, and the rudder and stock removed. During the process of measuring the bearing clearances it was found that the lower stock bearing was badly worn to one side of the bush. ‘Kaharoa’ had a previous history of steering issues, so the rudder and prop shaft components were put back together in our workshops, checked, and found to be significantly misaligned.

The rudder stock was put on a lathe and the palm face machined true. The rudder itself was set up on the horizontal borer and also machined true. The palm fitted bolts were in poor condition so these were also replaced and a new lower bearing was fitted to the rudder stock before the steering assembly was refitted to the vessel. Steering rams were also overhauled, with the tiller arm blasted and painted. New hydraulic hoses and grease nipples were fitted and the system was synced to the autopilot.

The variable-pitch propeller was removed from the vessel and transported to the workshop, where the blades were removed from the hub and O-rings and PTEF rings replaced.

The propeller shaft bearing assemblies were removed and the bolting surfaces cleaned up in readiness for new seals. Bearing surfaces were measured and recorded, followed by the reassembly of the shaft to the ship. Once connected to the gearbox the pitch control push rod was integrated to the electronics before finally completing the assembly of the muff coupling, setting up the preload on the seal assemblies and filling the system with oil.

The controllable pitch propulsion (CPP) gearbox’s forward seal on the thrust shaft was leaking badly and, on inspection, the sealing surface to the shaft was found to be damaged, which meant dismantling it - from the gearbox aft to the clutch assembly. Together with the shaft, the coupling was removed along with the seal, bearings, sleeves, locking nut and tab. One bearing was replaced, another was cleaned up and refitted and a new sleeve was fabricated. With the shaft now reassembled it was taken back to the vessel and installed.

With survey work such as this, you don’t know the full extent of work until you begin. The ‘Kaharoa’ survey started with some 20-25 defined jobs - but jobs can ‘grow’ very quickly! A leak in the captain’s cabin ensuite had been reported. It appeared that water had got under the flooring vinyl, but when that was pulled out, everything was found to be rotten around it, under the toilet area, and there was water under that as well, due to a pipe leaking - so the pipes and the entire floor had to be repaired!

‘Kaharoa’ works up in the Islands from time to time and various jobs were required to her interior accommodation areas. These included insulation of the condensate line for the air conditioning system. 

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