The introduction of the Sea-Land class of container ships marked a striking advance in the speed and size of container ships; being owned by Sea-Land Services, part of the RJ Reynolds Industries Inc organisation.
These vessels were the subject of intensive series of investigations, not limited to hull form, sea keeping and propulsive qualities etc, but also included manoeuvring characteristics and mooring configurations at various states of tides and wind at the three terminals, Rotterdam, Bremerhaven and New York.
Sea-Land initially considered the feasibility of a high speed twin screw container ship as far back as 1957 for the North Atlantic service, envisaging a 904.5ft overall long ship with a container capacity of 944 units propelled by machinery developing 54,000 SHP to give a service speed of 23 knots. Given the then current high cost estimate for this proposal it was put in abeyance.
Later again in 1966, this type of vessel was considered with a length of 910 ft and 103 ft beam, but with the significantly higher power of 72,000 SHP to give a service speed of 25 knots, intended to carry 1,236 – 35 ft and 40 ft boxes. A brief specification and semi-contract drawings were provided with the assistance of the well known consultant naval architects George Sharp & Co, but whilst the design found favour again the cost was considered too high.
Sea-Land Inc owed its origins to the man who is generally accepted as the father of the modern container industry, namely Malcolm McLean, who with hard won experience fully understood the mechanics of land based side of cargo movements, and soon realised that speedy movement afloat could be nullified by a more lethargic organisation who were involved in the subsequent movement of cargo.
However Sea-Land were initially acquiring old ships from the US Reserve fleet and converting to container carrying, and the economics of operating these relatively slow speed ships at a speed of under 21 knots were against the introduction of new tonnage of advanced design.
It was obvious that the passing years would see the supply of suitable reserve vessels diminishing, and thus Sea-Land would not remain competitive in a growing industry. New vessels were therefore needed, and studies indicated that to maintain a weekly, bi-weekly or even tri-weekly service on most trans-ocean routes would require a service speed of 30 knots, with maximum of 33 knots on certain routes, a speed that would require around 120,000 horsepower, considered the then maximum possible on twin screws.
About this time, in 1968, the General Dynamics Co of US had completed a study for a container ship of 30 knots. It was approached by Sea-Land to define the feasibility of this project, resulting in an acceptable cost estimate, but as the design did not meet Sea-Land’s requirements the New York naval architects JJ Henry Co Inc were instructed to draw up the final design, resulting in the designation S.L-7 type, which in fact was the outcome of a number of prototype designs.
Extensive model tests were completed by mid 1969, and after 9 months the designs were ready to put out to tender, the specification being such that the ship could traverse the Panama Canal and a service speed of 33 knots. Tank tests were conducted at the Wageningen tank in Holland, testing six models by the designers, in the end however the final lines, propellers etc were designed by the Model Tank.
For such high power steam turbines were the obvious choice, whilst gas turbines offered the facility for easy removal and low weight it was considered that insufficient experience had been gained, despite the undoubted success of the Seatrain gas turbine ships, albeit being smaller and lower powered.
In the end Sea-Land opted to adopt well tried and reliable steam turbine machinery to ensure reliability for such tight schedules.
Read the rest of this article with additional pictures in Sea Breezes Magazine - January 2011 Issue
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