Distances from BL and CL

Frame positions are in most cases defined at those locations along the ship where there are transversal hull members, either frames or webs,

In a similar way there are in most ships characteristic distances from the Center Line (CL) and above the Base Line (BL) where hull members are located. for example, longitudinals in the bottom and in the side in the midship section are located at positions which normally also define the position of stiffeners in decks, platforms, bulkheads, , and the position of girders. By referring to these positions one may define locations along the y- and z-axes as simple as for example, Y=LP10 +100 and Z=LP35 -100. (LP10 +100 means 100 mm in portside direction from Longitudinal Position number 10 in the bottom, LP35 -100 means 100 mm below Longitudinal Position 35 in the side).

From a practical point of view it is recommended to let the longitudinal positions and their numbers coincide with the numbers and positions of actual longitudinals in the midship section. However, it should be noted that the longitudinal positions form a grid that need not have any direct relation with the physical longitudinal frames. for example, if some longitudinals are replaced by girders there are "holes" in the numbering of longitudinals. However, the longitudinal positions should include all the positions, also those where there are no longitudinal frames. The figure below shows schematically a typical midship frame with suggested longitudinal positions.

Figure 7:1. Midship section with longitudinal positions.

The point as the cross in the figure above may be located by Y=LP6, Z=LP26.5

The following rules should be considered:

• The positions and the numbers should be related to those of actual longitudinal frames, if possible.

• The longitudinal numbers should be in the interval [0,999]

• The numbers for horizontal positions (along the y-axis) and vertical positions (along the z-axis) should not be the same.

• It is quite possible to define a longitudinal position in the CL plane, that means, where y=0. This position may have number 0.

• The relation between increasing/decreasing numbers and increasing/decreasing distances is arbitrary similar to what is stated for frames. This should be decided by the rules for longitudinal numbering, used by the yard.

• The longitudinal numbers and their positions are stored in a table set up by the customer (thus, there is no direct connection to the generated physical longitudinal frames).

• Longitudinal positions in the bottom are normally only defined on portside. Reference to the corresponding positions on the starboard side is done by negating the longitudinal number, for example, Y=LP-20+100.