The two submarine pipelines described by the Authors in 5 75 represent a total capital investment of about L14 000 000 and they appear to be the largest examples of this class of work yet undertaken in British waters.95. Increasing use is now being made of submarine pipeline techniques in other fields and it would be useful if the Authors could give some more information about the design of the natural gas pipelines in relation to sea bed conditions. In 5 78 trenching depths of from 4 to 10 ft, according to location, were mentioned and it would be interesting to know what minimum depths of cover were specified. From 5 81 it appears that the pipelines may remain exposed for several months before becoming buried by natural sand movements. Were the pipelines in operation during this period and was the risk of damage by ships' anchors considered to be negligible?96. Finally, it appears from 5 77 that the thickness of the weight coat has been increased where the pipelines are within territorial waters. The limit of territorial waters is a notional line, not connected directly with either depth or sea conditions, and it would be helpful if the Authors would explain the reasons for the adoption of a more expensive form of construction within this line. M r A. M. Muir Wood, Sir William Halcrow and PartnersAn unsuspecting reader of $5 45-49 might suppose that a fully sufficient theory was available for the calculation of wave force against a drilling platform. I suggest to the Authors that the following factors are among those that require considerably more study before there can be any complacency among engineers responsible for designing such structures.98. While the higher order wave theories (or Cnoidal wave theory in shallow water) may appear better to represent the particle motions of steep regular symmetrical waves, they take no account of important modifying effects such as eddy viscosity. Moreover, in many marine applications, the irregular, short-crested and asymmetric wave of the open sea is found to have significantly different effects on structures than the long regular wave of the wave theories.99. Considerable doubt is attached to the evaluation of the inertia and drag coefficients and it is highly improbable, from fundamental considerations, that these are each constant through a wave cycle as frequently assumed for marine structures.100. Knowledge of the motions of the incipiently breaking wave relies more on experiment than on theory; this is often the most critical type of wave for an offshore platform but is such a rare event at the situation of a platform that few full-scale recdrds are available.101. Where, on account of steepness of the wave or the slope of the structural member, the motion of the water is inclined obliquely to the axis of the member, the inertial and drag coefficients will be varied in consequence.102. The vortex street that forms in the wake of a cylinder in a steady current causes a cyclical variation in drag and in lift (i.e. the lateral force perpendicular to the direction of ...

In amplification of 0 51, the tensile shaft friction as estimated by the geotechnical consultant was exceeded by 23 times.69. Perhaps the greatest achievement of the Kharg 4 project is the fiscalized metering system with its design tanker loading rate of 30 000 ton/h, using ten 18 in.. meters of 0.02% repeatability and +O.lO% linearity. This is by far the largest capacity system accepted by any government, without recourse or reference to tank dipping measurement. My colleague Mr Dennis was concerned with a not dissimilar structure in the Persian Gulf at Khor-al-Amaya where the mooring dolphins were formed from jacket structures rather than cantilever tubes. Could the Authors say how the tube dolphins have behaved under repeated loading, and give some more information on the distribution of the berthing energy between the 3-and 4-pile berthing dolphins on the main berth.71. It is always a difficult problem, in designing these structures, to decide how the energy should be distributed between fenders as close as these. The outer one must be capable of dealing with a ship berthing at an angle. The Authors make some comment on this but it would be useful to know how the maximum energy is distributed between the two groups. 72.In 0 52 reference is made to the difficulty of placing the jackets within the prescribed tolerance. At Khor-al-Amaya terminal bedding mats were used for the first jacket templates, but these seemed to do more harm than good and were subsequently omitted. Were such mats considered for Kharg Island?73. On this job there were problems in making the connexion between the fabricated deck and the piles. It is not clear from the Paper whether the deck was carried on the jacket templates or on the top of the piles. Tn either case, one can visualize that there is a problem in getting the deck set horizontally if the jackets have not settled down level.74. There seems to be some discrepancy between the pile tests and the results of the soil investigations. Has any further analysis of this been done to determine where the discrepancy is? It was obviously encouraging that in the short term the results of the tests showed that the ground was very much better than expected, but it would be interesting to know whether the long-term tests were carried out to see if the behaviour of the clay deterioriated over time.75. When fixing the deck structure units, it may be difficult to make the welded connexion to the piles due to inaccuracy in location of the pile and the necessity to achieve the correct root gap for the weld. Can the Authors comment on this and on any particular type of connexion which was found to be satisfactory while affording some positional tolerance?76. Now that the structure has been in use for some time, would it be possible to have comments from the Authors as to the difficulties which have arisen with the operation of the structure itself and the equipment installed on it.

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