GL revises construction rules

The Construction Rules for the hull structures of seagoing ships have been revised by Germanischer Lloyd (GL) and adapted to meet the changing international requirements. The new construction rules for shipyards apply with immediate effect to all newbuildings contracted after publication of the revised edition.

In accordance with the specifications of the International Load Line Convention (ILLC), the design loads for hatch covers have been adjusted. Here the permissible stresses and deformations have been modified due to a net scantling approach to match the design loads. As a consequence of this net thickness concept, the required corrosion additions for hatch covers and hatch coamings have been worked out in detail by GL depending

on the ship type, exposure (weather, longitudinal strength) and specific structural element.

SOLAS regulation II-1/3-6 as well as the rather extensive technical requirements of the applicable Resolution MSC 158(78) regarding access to the cargo area of oil tankers and bulk carriers have been incorporated.

For passenger ships, an adjustment of the Rules to the new SOLAS regulations II-1/10.3 and 10.4 was carried out, which concerns requirements for the collision bulkhead and its extension above the bulkhead deck respectively.

Regarding the rules for tankers, the criteria for the strength analysis of the cargo tank area by means of the FE (finite element) calculation method have been rendered more precisely. This concerns on the one hand the definition of loading patterns to be considered, related to specific cargo tank arrangements, and on the other hand the evaluation of fatigue strength which may include an examination of structural details by means of local FE models. For large tankers having a transverse web frame spacing in excess of about 3.3 m, reinforcement of the side shell plating in way of the berthing zone will be required.

In the section about longitudinal strength, load cases and related design stresses have been summarized in tabular form. In addition, some definitions were amended and illustrating figures provided. In the formulae for torsional loading of the hull and the resulting warping stresses, some single factors have been modified. Furthermore, the

procedure for approval of the loading instrument was newly stated.

A method for approximate calculation of maximum notch stresses in cut-outs in case of superimposed loading was added by inclusion of the corresponding formulae.

Notes and recommendations of GL regarding avoidance or decrease of structural vibration in way of the propeller and in the engine room have been worked out to obtain a detailed set of criteria. Also, the most important recommendations of a recent technical

publication by Germanischer Lloyd as regards measures to decrease or avoid rudder cavitation have been included.