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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
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
