Page 41: of Maritime Reporter Magazine (October 1993)

rules since 1986.

Recently, GL was commissioned by the five European shipyards in- volved in the development of the E3 double-hulled tanker to calculate and assess the collision resistance of this vessel. The 280,000-dwt ship has a capacity of two million barrels and is designed to fulfill all of today's environmental regulations, as well as those expected in the future. The assessment of collision resistance was based on a collision between two moving vessels of the same size, and between a moving vessel and a stationary vessel, with variation in the draft of both vessels. Two differ- ent bow shapes for the striking ves- sel were investigated: a bulbous bow and a raked bow (see Figure 1).

GL is also breaking ground in the technology of surveying older tank- ers and bulk carriers. The methods used so far have been based on the principle of visual inspection by com- petent experts, supported by thick- ness measurements. The selection of the areas of the ship to be sur- veyed and measured has, to a large extent, been concentrated on sus- pected weak spots, and has depended on the experience of the surveyor. It has not been possible to predict and localize these areas with precision.

The difficulty has been exacerbated by the extremely tight schedules under which the surveyors have to work.

The result has been that deci- sions affecting the current and fu- ture safety of ships have been made under far from ideal circumstances.

This was of less importance in ear- lier times when ships were smaller and of considerably higher residual strength, but is not satisfactory for the older, larger vessels now at risk.

GL has begun to break new ground by bringing sophisticated computer and laser measurement technology to bear on the problem.

This is being supported by pressure tests to determine deformation of bulkheads and outer plating under load, and by measuring and analyz- ing the natural vibration of the ves- sel. These calculations should pro- vide a much more scientific basis for the surveyor before commencing a visual survey.

All this enables a visual display computer model to be built up (see

Figure 2) showing all of the struc- tural components of the ship with their permissible corrosion allow- ances. From the thickness mea- surements of many investigations by GL surveyors throughout the world, the critical areas are deter- mined in relation to the ship type, and are incorporated into the model.

In this way, a forecast can be made of the structural strengthening that may become necessary at a later stage, or the operation limitations that may have to be imposed on the ship. It will also permit additional strengthening calculations to be made without any great additional effort. We believe that these sophis- ticated models will mean that the existing procedures for classifying the older, larger vessels, will change soon, and that GL will once again have made a significant contribu- tion to safety at sea.

October, 1993

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