The purpose of Section E.4.2 is to determine the value of "tb" to be used in Section E.4.1 for the computation of "wl". Section E.4.2 does not imply that the thickness of the bottom shell course should be increased.

Section E.4.2 details the determination of "tb" as follows:

1) The actual thickness of the bottom plate may exceed the value used for "tb" ...

2) however, the value used for "tb" in the calculation of "wl" shall not exceed the larger of 6mm (1/4 in), or the thickness of the first shell course less any corrosion allowance. Computationally, this can be expressed as: tb1 = max( 0.25, (t1-corr) ).

3) Additionally, tb shall not exceed the actual thickness of the bottom plate under the shell, less corrosion. Computationally, this can be expressed as: tb = min( tb1, (tbott-corr) ).


------------------
Regards,
Richard Ay (COADE, Inc.)