Specified operating area service notation nautic.

[Julchonok]

Добрый вечер! Скажите, что означает specified operating area service notation? Заранее спасибо!

For ferries and passenger ships classed 100A1 with a specified operating area service notation, the bottom and side shell minimum thickness at ends may be taken 20 per
cent less than that required by Table 2.4.1 and Pt 3, Ch 5 and Ch 6, but is in no case to be less than 6 mm.