How the classic hulls were created

fred henderson
13th September 2005, 18:52
As this is a ship nostalgia site, one of the greatest interests of the members is in ships of the past. Not all members may appreciate that ships built over 50 years ago looked different from today because they were built differently. The first area of difference is the way that ships were conceived.
In the past, design and drawing offices undertook less detail work than today. The group of building drawings that created the form of the hull was made up of three plans: -

1. The sheer draft, which gave the profile, frames, position of decks, bulkheads, etc.
2. The half-breadth plan, which gave viewed from above the waterlines and beam end lines.
3. The body plan, which showed the body shape in a series of transverse sections.

Ship details often refer to the length between perpendiculars (LBP). The fore perpendicular is a nominal vertical line at the point where the loaded waterline meets the stem. The aft perpendicular is the axis of the rudder. The LBP was divided into an even number of equal spaces, giving an odd number of “displacement stations”. The Body Plan showed on a single drawing, the transverse shape of half of the width of the ship at each station, from the bow to the broadest part of the ship on the right of the middle line, from there to the stern on the left.
All these drawings were made by hand to a scale of ¼ inch to the foot. They were then issued to a building known as a “Mould Loft”. I have posted a photo of the old Hawthorn Leslie mould loft in my gallery.
It was a very large room with a matt black painted wooden floor. The lines drawings were chalked onto the floor at full size. First a centre line was established. Then in plan view the displacement stations were measured and drawn on the floor at right angles to the centre line. The distance from the centre to the side of the hull at the waterline was measured on the bow view body plan, then marked out full size on each displacement station line. A long flexible batten was laid through these spots and the inevitable minor deviations corrected on the floor and the plans. When all of the lines in the drawings had been cross referenced at full size and were confirmed or corrected in this way the ship was said to be “faired”.
The faired lines corresponded to the outside of the shell plating and with riveted plating worked on the raised and sunken system, in order to obtain the frame lines 1½ times the plate thickness was measured in at the waterlines. The frame lines were then scrieved in on the body plan and the displacement stations rubbed out. Only then was it possible to make the patterns needed by the frame bending shop.
Whilst the frame patterns were being made, a wooden, scale, longitudinal half model of the ship was made from the revised drawings. Depending on the size and complexity of the hull, this would usually be 3 to 6 ft long. It would be painted matt white and all of the plate lines and overlapping joins, plus all frame positions, openings, brackets and other structural details inked in to scale. This model would be used in conjunction with a shell expansion drawing to identify and size every plate to enable the steel to be ordered. This work would also establish the degree of taper and the position of the rivet holes to be applied to each flat plate, prior to it being rolled into shape to fit the curvature of the hull.
The work in the mould loft was the highly skilled key to translating and refining the designer’s requirements into a format that could be used by the production workers.

Fred

michael james
13th September 2005, 19:53
Fred, What a great explanation. I was not fortunate enough to experience a visit to a shipyard whilst building was in progress, your description gives an insight into what is involved, from plans to plating.

I did watch facinating work going on at Smiths Repair yard whilst I was on "standby" on a Brocklebank ship there for minor repairs, the skill involved was enthralling for anyone with a mechanical bent like myself. Thanks very much for posting.

fred henderson
13th September 2005, 22:44
Fred, What a great explanation. I was not fortunate enough to experience a visit to a shipyard whilst building was in progress, your description gives an insight into what is involved, from plans to plating.

I did watch facinating work going on at Smiths Repair yard whilst I was on "standby" on a Brocklebank ship there for minor repairs, the skill involved was enthralling for anyone with a mechanical bent like myself. Thanks very much for posting.

Thank you Michael. I am sure that there is not a traditional Mould Loft left anywhere in the world, which is why there are no new ships that have traditional looks.

Fred

Tmac1720
13th September 2005, 22:49
You are quite correct Fred, Mould Lofts are no longer used in shipbuilding it's all computer generated lines now, the old skills have sadly died away. Actually this can cause problems with ship repair we (H&W) had a major repair job in but the vessel had no lines plan. None of the draughtsmen knew how to lift a hull sight and so we had to bring back some of the "old school" draughtsmen who had the skill to use a dumpy level and take hull sights. Just goes to show that progress is not always what it appears to be.

Tmac1720
13th September 2005, 22:52
Just an after thought, I'll post a few of the old lines plans I have in my archive just for interest. The classic shipbuilders profile should make for interesting comments.

fred henderson
13th September 2005, 23:16
Just an after thought, I'll post a few of the old lines plans I have in my archive just for interest. The classic shipbuilders profile should make for interesting comments.

Great idea Tmac, all that I have are Crown Property and although the ships were turned into razor blades decades ago they are still probably covered by the Official Secrets Act.

Ship repair is the last home for traditional skills. About 35 years ago I was in a meeting in Wallsend Slipway. They had a Russian ship in dock. During the meeting the Shiprepair Manager put his head around the door and asked "Is there anyone here who knows about wood fired boilers?"

Fred

R651400
14th September 2005, 03:08
Fred and Tmac, thanks for an insight into the womb of my chosen metier.
Tmac you will be pleased and hopefully proud to know that yours is the only gallery I have gone through from beginning to end in one go.
Passing down Govan by tram in the mid fifties, this very young MN lad gave little thought to what was going on in the various yards and slipways.

Tmac1720
14th September 2005, 17:25
Fred and Tmac, thanks for an insight into the womb of my chosen metier.
Tmac you will be pleased and hopefully proud to know that yours is the only gallery I have gone through from beginning to end in one go.
Passing down Govan by tram in the mid fifties, this very young MN lad gave little thought to what was going on in the various yards and slipways.
Malcolm, I am delighted you have enjoyed the gallery, I have lots more photographs so hopefully you will see much more to your liking. Thanks for the kind remarks I really appreciated it. (Thumb)

Pompeyfan
15th September 2005, 12:03
I know absolutely nothing about ship design other than the fact the former passenger liners and I assume cargo liners were designed to cope with heavy seas. I say this because the designer of QM2, S.M Payne said in a letter to Ships Monthly a few years ago that QM2 was designed to be at home in the hostile North Atlantic saying that the boxy design of modern day cruise ships with their boxy characteristics making them totally unsuitable for the winter North Atlantic route which explains why they are not employed on it. But on first sight, QM2 looks a bit boxy to me. In fact, I think she rolled like mad on her maiden voyage. But like I said, I know nothing about design, and just quoting what S. M. Payne said. He wa responding to a letter complaining about the design of QM2 returning to styles of yesteryear rather than sticking to modern beauties(the letter writer words not mine)such as Explorer of the Seas. Mr Payne went onto say magical words to my ears that QM2 was not only designed for the trans-Atlantic but was the first true liner for 34 years since QE2. He told the writer than Explorer of the Sea was a cruise ship, not a tran-Atlantic liner.

Whether any of this has anything to do with ship design as posted by Fred, I am not too sure. But it could well explain some of it?. David

R58484956
15th September 2005, 12:33
For rough weather north atlantic take a look at MV Selkirk Settler http://tv-antenna.com/heavy-seas/