Day Two; Between the Times 17/10/2008

Onslow entering Captain Cook Grave Dock

Onslow entering Captain Cook Grave Dock

Today is much like the last only lacking all the fanfare. Again, our Navy pilot boards and the DMS tugs come along side. Under the watchful eye of the jaunty dockmaster we’re eased into the Captain Cook Graving Dock, one of the true industrial cathedrals, but today it looks more like an over sized swimming pool. Secured well back in southern eastern corner of the dock, Onslow will stay in this position until the pump-out of the dock commences next Friday, being joined by the museums light ship  CLS 4 (commonwealth light ship) and thales’ floating dock. There is not a lot happening for the rest of the day so I’m off back to museum to organise some supplies.

CLS4 being manoeuvred within the garve dock

CLS4 being manoeuvred within the garve dock

This seems a good time to discuss the work that will be undertaken during the following week, but first, a bit of ‘submarines for dummies.’ Essentially, the submarine is a habitable metal tube (the pressure hull) which gains buoyancy from the saddle tanks attached to the greater part of either side of the vessel. As I explain to our younger guests at the museum, these tanks are much like floaties, when full of air the sub remains on the surface. Release the air and she submerges below the waves. Luckily all submarine have the ability to re-inflate their floaties and re-emerge on the surface.

The next point is that what you see is not what you get with a submarine. On the surface she appears to be ominously sleek and other worldly but lift the bonnet, or more accurately the casings, and much of the mystery is removed. The casings, over twenty in number, sit atop of the pressure hull and run near the full length of the hull. Made of either mild steel or GRP (glass reinforced plastic) their primary function is to give the submarine a hydrodynamic shape; they also provide protection for the equipment that lies below them as well as giving a work platform when the sub is surfaced. Compressed air bottles, exhaust manifolds, sonar arrays, webs of pipes and a menagerie of equipment are housed underneath the casings. With their removal, many of the functions of the sub and the means with which they are attained come to light. The dark menace is shown to be just a bunch of nuts and bolts, although a very a very complex bunch.

Channel, where saddle tanks and pressure hull meet

Channel, where saddle tanks and pressure hull meet

Onslow; featuring saddle tanks and casings

Onslow; featuring saddle tanks and casing

So why does Onslow needs to be docked? The three main aims of the docking are to make sure she remains afloat, preserve the vessel’s exterior and to improve the boat’s aesthetics. These three aims are intertwined. In this first week, prior to the pump down of the dock, the lifting of eleven of the GPR casings will be the main event. This will allow access to areas that would, without a team of highly trained spider monkeys, be impossible to reach, and its purpose involves all three aims. One of the critical areas, in regard to buoyancy, is the point at which the saddle tanks join the pressure hull. The surrounding area forms a gutter, collecting water and leaving it susceptible to corrosion and the possibility that the tank’s watertight integrity could be breached. It is essential that this area be well preserved. If the casings were left in place there would be very restricted access and a great risk of the fibre-glass casings being damaged from the water and grit blasting that will take place later. The blasting will remove most of the corrosion on the pressure hull and pipe work, in preparation for preservation via painting. With the source of most of the rust staining along Onslow’s sides no longer present, she will look better for longer and will probably have lost a couple of kilos. The docking is much like the combination of a detox diet and trip to the day spa, you’re healthier, you look better and it often stops that sinking feeling.

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