In the Bowels of the Ship.

5th, 2012
Share This : Share on FacebookTweet about this on TwitterShare on Google+Pin on PinterestShare on TumblrShare on VKShare on LinkedInDigg thisShare on RedditShare on StumbleUponPrint this page

 

It occurred to me that when working in the hold (inside bottom) of a ship one tends to ignore, or perhaps forget what lies on the other side of that inner hull. Discovery was for much of the first half of the Project in dry-dock so the air in the hold of the ship was, by and large, the same as that on the other side of the inner hull. When she was afloat the level of the water on the outer side was 12 feet (3.7 metres) above the keel, in other words nearly two metres above the average person’s height. The deeper the water the higher its pressure, so all around the ship the water was pushing trying to get in! Ships, all ships and boats, are designed to withstand this pressure and float. An interesting and perhaps more frightening statistic is that of the deepest drafted oil tanker when loaded. The depth of water from her keel up her sides was (I say was because these ultra large ships were scrapped some time ago) 28.5 metres (93.5 feet). Imagine working in the bottom of the engine room of that ship knowing (or forgetting) that the depth of the water outside, above you, is nearly 27 metres above your head. Quite a thought! So visitors when touring around Discovery’s hold area remain blissfully unaware that they, in fact, are walking underwater. I suspect those who may be of a more claustrophobic nature would want to get out pretty quickly!

I told of the two dimensional replica packing cases that shut out the ventilation in the previous part of this story. The two following pictures show these as they were at the beginning of 2008. The arrow points at one of the huge Oak beams that ran across the hull in the lower hold. This one had been cut to allow through access from aft to forward and vice-versa.
I promised I would show more of the unique construction of Discovery in relation to the magnetic free area around the observatory. This area was situated just forward of mid-ships (forward of the centre of the ship) and had a radius of 30 feet (9.15 metres). When the replica packing cases were removed we found large, forged, naval bronze, beam knees (metal angles that tied the cross beams to the vertical frames). We knew they were there of course but they had been hidden by the false replica wall for years. Not only that, the damp conditions around them had allowed electrolytic corrosion to attack the fastenings and in places the inner planks showed signs of breaking down to their chemical component parts. The Lignin or Lignen (the component that holds the fibres of timber together) had been the first to suffer leaving the cellulose residue of the fibres coating the outer surface. The photos show the residue and the beam knees:
As the false partitions were taken down, the inner ceiling (that’s the naval term for the side) dried, cleaned and coated, the whole of the atmosphere in the lower hold changed significantly. Not only was ventilation restored but the whole of the wooden construction elements were made visible. In the picture of the beam knees I have drawn an arrow to highlight what looks like rectangular pigeon holes in the side planks between the frames of the ship. This was another secret of those who designed her and makes one realise that in 1900 the preservation of the timbers of the outer and inner hull of the ship was uppermost in the minds of the architect who was involved. He knew that Rock Salt, and salt generally, had preservative qualities in relation to timber. It is a very fine line between decay and preservation so far as water is concerned. Fresh water with a density of 1,000 g/cm3, is harmful to timber; whereas salt water at a density of 1,025 g/cm3 acts as a preservative. Knowing this and knowing that the upper deck of the Discovery would, through the stresses placed upon it, leak from time to time, even though the Bosun would have had a running plan of repair and maintenance. So rain water would find its way down the ships side of the inner hull and if left untreated would slowly eat away at the timbers. The treatment involved Rock Salt being fed into the pigeon holes to form a solid barrier behind the inner planks and frames, right from the upper deck to the bottom. So the cunning plan evolved! The fresh water that found its way between the frames and planks at the upper deck level, as it seeped down it was absorbed by the Rock Salt and slowly turned from a fresh to a saline solution.

With a walkway being constructed much earlier through the holds of the ship to allow visitors to safely travel through, doors had been cut through the once watertight bulkheads (a bulkhead is of solid construction that runs across the width of the ship at designed intervals). How these bulkheads were constructed is another feature of note. They were built of pitch pine, double diagonal planking, not the conventional vertical or horizontal but diagonal with
the diagonals on one side going in the opposite direction to the diagonals on the other. This gave the bulkhead a very strong resistance to horizontal forces. If an individual compartment was flooded by accident, incident or design the ship would remain afloat supported by the buoyancy of the other compartments since the flood water would have been contained between two watertight bulkheads.
The photograph shows the diagonal planking on what was the watertight bulkhead at the forward end of the coal bunker under restoration. The persons in the blue overalls are real, the one on the left is a dummy stoker holding a shovel.

Next issue we enter the world of high tech, bringing the modern methods of gathering information and using it to the best advantage for the future conservation of the ship.

© Captain John J Watson OBE January 2012 Fethiye

News 668 views
Tags: