What Is the Transverse Plane?

The plane passing through the upper edge of the flat plate keel in the middle of the hull and parallel to the load horizontal plane is called the base plane, which is represented by the H plane. ^[1] During the ship design phase and after the hull construction is completed, the dimensional basis for determining the shape and position of the hull is a three-base system. The three base plane system is composed of three mutually perpendicular planes, which are also called main coordinate planes in shipbuilding terminology, which are base plane, midline plane and middle station plane. ^[2]

The base plane is a horizontal plane made through the intersection of the hull keel line and the center station line. The midline plane is a longitudinal plane that is perpendicular to the base plane and divides the hull into symmetrical left and right sides. The mid-plane is a transverse plane perpendicular to the base plane and the mid-line plane, which is made across the midpoint of the design waterline length or the midpoint between vertical lines. ^[2]

The base plane, midline plane, and mid-plane plane are the basis for expressing and measuring the shape of the hull, and also the basis for expressing and measuring the positions of various components and equipment in the hull. The base plane is the datum in the hull height direction, the midline plane is the datum in the hull width direction, and the mid-plane is the datum in the hull length direction.

Because of the large size of the hull and the complex shape and structure, these three reference planes are not enough. Therefore, some other benchmarks are derived from these three reference planes, mainly: the waterline plane as the reference of the hull height direction, the station line (or rib surface) as the reference of the hull length direction, and the width of the hull For longitudinal sections and so on. On hull design drawings, their projection lines are generally used. The hull baseline, center line, center station line and waterline, station line (rib line), longitudinal section line, etc. are used as the hull height, width and length reference, especially as the reference of the hull length direction. Use vertical lines (civilian and auxiliary ships), or vertical lines (military combat ships) and rib lines. ^[2]

Take a number of horizontal sections at equal intervals along the draught direction parallel to the base plane. The curves obtained by intercepting the shape of the surface of each horizontal section are called waterlines. When the waterlines are superimposed on the base plane, the waterline diagram is obtained. Numbering the plane upwards is also called the half-width waterline diagram because of the symmetry of the hull, which can only draw half of the waterline. And because the waterline on the maximum waterline surface of the hull is very close, for clarity, the waterline on the upper and lower surface of the maximum waterline is drawn on two figures respectively, so the half-width waterline diagram contains two sets of curves. ^[3]

The base plane, midline plane and mid-station plane are the three basic planes of the hull. These three planes are both ships

figure 1

Datum plane for volume stakeout. It is also the reference plane for structural positioning in hull assembly. The baseline, centerline, and center station line that are accumulated after the three plane projections are the positioning reference lines when the hull is closed on the platform, as shown in Figure 1. The intersection of the centerline plane and the center station plane can be regarded as the Z axis, and the intersection of the centerline plane and the base plane can be regarded as the X axis. The line of intersection between the middle station and the base plane can be regarded as the Y axis.

The necessary reference lines are marked on the platform and in the dock as the basis for segmentation positioning. When the slipway is closed, the segment is centered on the center line or the designated rib line in the direction of the captain. Use the midline or the specified longitudinal section line as the reference for positioning in the ship width direction. In the height direction of the ship, the baseline or the designated waterline is used as the reference for positioning. As shown in Fig. 1, the positioning dimensions X, Y, and Z are based on the centerline, centerline, and baseline respectively. The measurement and inspection of the horizontality, verticality, and inclination of the component during assembly actually limits the rotation of the component about the X or Y axis. ^[4]