Hull construction

HULL CONSTRUCTION & KEEL

Balmoral is a traditionally built ship with a steel hull. The first ships used wood, then in the 19th Century iron was the new material, as used by Brunel in the Great Britain further down the Docks, although Balmoral is actually moored over the place where Brunel's first ship, the Great Western was built and launched! In the early part of the 20th Century, steel became available. This was a form of iron with additional chemicals that made it more flexible, much less brittle and easier to work.

RIVETS AND WELDING

Originally iron ships were held together with rivets. These were plugs inserted through matching holes in the plates and formers. They were red hot when put in. This caused them to expand slightly and red hot metal is softer than cold, so they were easier to form. The rivets were heated up next to the ship, inserted into the holes with tongs and and were hammered flat on the inside of the hull where they poked through, so that as they cooled and contracted, the sheets of iron were pulled together. This gave a very strong and watertight joint, but it was slow and time consuming to put together and incredibly noisy as all the rivets had to be hammered flat with a machine or in the early days, a man with a sledge hammer !

As the 20th Century progressed, steel was used rather than iron, and this was much better for building because it could be formed and was also stronger for a given thickness, although it did rust much faster, particularly in salt water ! The other great advantage was that steel could be welded together. This involves using a very high electric current to melt a stick that is pulled over a joint between two pieces of steel. The intense heat melts the stick and softens the metal on either side of the joint so that they all fuse together and form a continuous waterproof join that is as strong as the surrounding material. Although mistrusted at first as some ships had brittle welds that cracked and cause the hulls to fall apart in rough seas, this was eventually resolved and welding became the standard way to build ships. It was cheaper, faster and used fewer men. It did produce a great deal of poisonous fumes and intense light that could damage people's eyes, but once these issues were controlled it soon became used for all ship building.

Balmoral is almost unique in that she uses a mixture of riveting and welding. She was built at a time when shipyards were changing over to welding but some ship owners still preferred the traditional rivets. Balmoral thus has a riveted lower hull and welded upper sections. Over the years as new hull pieces have been added to replace rusty sections, the new parts have been welded into place, so she is something of a mix and match these days, but there is still a lot of riveted metal in the ship and it is easy to spot.

This is an example of welding. Each steel plate has been joined by melting a welding rod into the surface, which leaves a tell tale bump with a series of ridges ( called a weave ). This is done by moving the rod slightly so that that the molten metal is mixed together and makes a stronger joint.

Here is a mixture of welding and riveting. The hull plates are welded together and the weave of the join can be seen, while the rivets s round the portholes how up as small regular rounded bumps and secure the frames that give the ship its shape and strength, to the hull. This is now a long forgotten way of putting a ship together but is incredibly strong if time consuming.

BILGES & BULKHEADS

Under the floor of the officer's quarters you can look into the very bottom of the ship, known as the bilge. This is the area where the keel is located. The keel is a very strong girder structure that is the first part of a traditional ship to be assembled, and everything is built up from it. In Balmoral's case it is clearly visible as a series of girders and steel plates running along the centre line. Running out a right angles are the ribs which form the curve of the sides and run upwards to the deck. They are the formers to which the steel plates of the hull are welded or riveted and Balmoral has one every 600 mm, which makes her hull extremely strong. Additionally a ships engines are extremely heavy and these are mounted directly to the keel of the ship which has a specially designed section. The keel is shown in blue on the diagram and the engines are clearly mounted on the raised section so that their weight is distributed evenly to the hull of the ship. If they were mounted on the plating that forms the skin of the ship they would break through and tear a huge hole in the bottom !

This is the bilge area under the officers quarters. You can see the centre keel section with the stringers either side and the riveted plates giving strength to the bottom of the hull. At the furthest end of the compartment is the bulkhead.

Most ships have dirty water and muck in this area. Balmoral was extremely well built and is looked after by dedicated volunteers. Her bilges are dry, clean and even painted as this photograph shows.

Another very important feature of the construction are the main bulkheads shown in yellow. These are watertight barriers that turn the bilge area and lower part of the hull as far up as the main deck into watertight boxes. These are designed so that if the hull is damaged and begins to leak water, the flooding will remain in a compartment and although the ship will float lower, it will not sink. The other use of the bulkheads is to maintain stability. If too much water enters the bottom of the ship, its centre of gravity will begin to rise and eventually it will roll over. Thus the bulkhead has two functions - it stops the ship sinking and also keeps it stable in the event of an accident. There are no watertight doors on Balmoral ! The bulkheads are completely sealed and the only way to get from one compartment to the next is by climbing up a stairway ( called a companionway on a ship ) and down another one into the next compartment. In this way the water can't leak from one to another ! You can see the heigh of a bulkhead by looking at the stairs to the lower bar. Add a bit more below the floor as in the picture above the diagram and that is the height ! The lower lounge/bar area is another watertight compartment. You would never know, but the top of the stairs are fixed to the top of the watertight bulkhead that separates this section from the engine room compartment.

When a ship is built, there are always more bulkheads at the bow and stern than in the middle. This is because most accidents result in damage to the ends, for instance if it runs aground, it will usually hit bow first. Thus there is a small sealed area at the very front( forepeak ), a collision bulkhead that is designed to withstand a major crash, and behind that are regularly spaced bulkheads for the rest of the length, followed by a smaller one at the rear that contains the steering and usually an auxiliary generator. Ships have an emergency generator somewhere above the level at which they could stay afloat with the maximum damage so that it won't be flooded and stop working.

Balmoral out of the water in drydock - and about to have a coat of paint. This photograph shows the part you don't normally see when she is afloat - like all ships there isn't much under the surface - that is because water is very heavy and ships, despite usually being made of steel, mostly contain air. The amount of water that would fill the hull to the bottom of the green 'boot topping' actually weighs as much as the whole ship with passengers, stores and fuel. The amount of water is called the 'displacement' and is the standard method of weighing a ship - in Balmoral's case this is approximately 700 tons. Water weighs 1 kg per litre and thus 1000 litres = 1 tonne.

When Balmoral was built in 1948/9, much of the steel used was imported from Germany and it is rumoured that military surplus was used for much of the hull and that some had come from a naval yard that was in the business of building German battleships! They didn't have much need for it by then and it was being sold off cheaply. She is certainly a massively strong ship and this may be one of the reasons she is still seaworthy. In 2017 we were replacing some of the steel in the after deck house by the Purser's office and it was necessary to drill the deck supports for new fixings. It was absolutely impossible to drill holes in the floor supports. We could make no impression at all on the material and eventually resorted to welding as no drill bit would even mark the surface. Our wise and knowledgeable Chief commented that he had been told Balmoral was built with steel intended for the Tirpitz's successors and he reckoned there is a piece of it supporting the purser !

............... and as a final photograph of rivets, here is the boiler and part of the hull of a wrecked ship, the 'SS Staghound' that was built in the 1890's, bombed and sunk during the Second World War, salvaged and then grounded and finally blown up to test explosive charges! Rivets are very strong indeed !

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