Anatomy of a Blueprint

OVERVIEW: While most people think of a blueprint as a guide for building a component or constructing a complex device, the type of naval blueprints most commonly seen are meant only for information. Similar to a general floor plan of a building, most naval blueprints fall under the category of "General Arrangement". Here, I will try to explain the different types of drawings and their purpose.


GENERAL ARRANGEMENT: General Arrangement plans are exactly what they sound like - plans showing the general arrangement of a space, usually from a top-down view. Some general arrangement drawings are only meant to show the dimensions of a space along with access to the space. These are sometimes referred to as "Compartment & Access" plans.

There can be varying degrees of details in a general arrangement plan providing only compartment dimensions all the way to specific equipment locations.


DECK PLATING: Deck Plating drawings are plan view drawings that show the layout and support of deck plating. Steel plating is normally expressed in pounds (marked "lbs" or #) with reference to a one foot square plate. A one square foot steel plate that is one inch thick weighs 40 pounds, so a plate referred to as 40 lb or 40# is a one inch thick plate of steel. A 3/16th inch thick plate of steel would be identified as 7.5 lb plate.

Steel type is usually identified as Mild Steel (MS), High Yield steel (HY), or Special Treatment Steel (STS). MS is used for normal steel structures and HY steel is used for high load or high stress situations. STS is used for light armor applications.


OUTBOARD PROFILE: Outboard Profiles normally show the starboard side of the vessel both above and below the waterline. Interior spaces are not identified. These profile drawings are a close representation of what the vessel would actually look like from a side view.

Aircraft carrier blueprints will often have both port and starboard outboard profiles given their asymmetrical nature.

Rigging Plans will usually be shown in profile view, but often lack the detail of a traditional outboard profile.


INBOARD PROFILE: Inboard Profiles normally show the inside view of the vessel looking from the centerline through to the port side. Interior spaces on the centerline identified. Outboard compartments may be (but are not always) identified using hidden lines.

Interior Profile details may vary from simple compartment access to complex equipment locations.


CROSS SECTIONS: Cross Sections, sometimes labeled as Sections Forward or Sections Aft, are half breadth drawings at specified frames looking either forward or aft. Occasionally sections are full width, but this is usually only done for asymmetrical ship sections.


MIDSHIP SECTIONS: Midship Sections are similar to Cross Sections but are usually full width and show much more structural detail.


SIDE PLATING: Side Plating is similar to Deck Plating except showing side views. Steel plating is normally expressed in pounds (marked "lbs" or #) with reference to a one foot square plate. A one square foot steel plate that is one inch thick weighs 40 pounds, so a plate referred to as 40 lb or 40# is a one inch thick plate of steel. A 3/16th inch thick plate of steel would be identified as 7.5 lb plate.

Hull Side Plating drawings are shown with all curved plating flattened, so the resultant hull profile is distorted.


STRUCTURAL DETAILS: Structural Detail drawings can cover anything from hatches and doors to armor plating and deck framing. Many of these drawings are of sufficient detail for a skilled tradesman to construct a component or build an assembly.


MOLD LINES or FAIRED LINES: These drawings provide a detailed representation of the complex curvature of the hull. They show half breadth, waterline (height), and end views.


TABLE OF OFFSETS: These tables are numerical measurements of the hull at specified locations. The measurements are usually provided in a Feet-Inches-Eighths format. A half breadth measurement of 10-5-1 would be 10' 5 1/8" from the centerline. Plus and Minus symbols are used to show finer measurements, so 10-5-1+ would be 10' 5 3/16" from the centerline.


PIPING and WIRING DIAGRAMS: These represent exactly what they sound like. They can be functional diagrams or actual location diagrams. This is normally clearly marked.