US NAVY'S - Incat

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Robert CLIFFORD Incat Chairman C LIFFORD’S O SPEED v PAYLOAD v FUEL L U M N It has come to pass that shipping speeds have slowed down in response to increased fuel cost. 28 knot container ships in many cases are now scheduled to sail at only 22 knots. Even slower speeds are likely as this trend continues. But, how slow is too slow There comes a point where more ships are required to serve the required schedule. More ships burn more fuel and increase capital costs. Nevertheless, continuous changes to the status quo are expected and will have wide ranging consequences. Fast ships can often burn more fuel than slower ships, but this is not always so. The real test is the weight of the ship that must be propelled through the water at a given speed. That is, a ship that is built of lightweight materials may displace less than half the water of a conventional steel ship. The lighter displacement allows the operator to either sail faster or install less power. We assume both styles of ship deliver the same payload per 24 hour day. If the lightweight ship is not required to sail faster the option of installing less power is attractive. Smaller engines burn less fuel and save even further weight that can further increase the payload. Consider also the heavy steel ship slowing down to make less revenue sailings per day, perhaps five sailings instead of six on a short sea route. The lightweight ship also has the option of sailing more slowly, perhaps ten sailings per day may be reduced to eight sailings; still three more sailings than the heavy steel ship can manage. There are endless permutations possible to save fuel and the fast versus slow, and the heavy versus light arguments must be analysed and considered carefully in each specific service situation. There is no simple answer, for example to slow down too much will result in either more ships being required to provide a satisfactory service, or cause the demand to be unsatisfied. Just making the ship lighter may be enough to achieve a higher speed without any increase in power. This on some routes will allow more revenue sailings per 24 hour day. 6 Incat THE Magazine Issue 36
Why Aluminium Why do we build our ships in Aluminium Why are 747s built of Aluminium Why are dinghies built of Aluminium The same answers apply to all - Imagine the power required to fly a jumbo made of steel, or rowing a steel dinghy! In all the above examples weight is the most important consideration. To the high speed ship low weight makes possible low fuel consumption and high speed. A conventional steel ship needing to service a 5000 pax per day market on a 70 mile journey will be able to make four crossings; 2 return trips, per day. The steel ship will displace about 10,000 tonnes of water - that is moving 10,000 tonnes of water aside as it progresses its journey. An aluminium ship can deliver the same 5000 pax per day to their destination faster on the same 70 mile journey and offer a greater choice of departure times with six crossings even though it could carry even more passengers by making eight crossings in the 24 hours available. The more frequent sailings also lessening queuing and road congestion by spreading traffic load across three or four arrival times rather than just two. On shorter routes the advantages of the lightweight are even more pronounced and that is why operators in the Canary Islands, Straits of Gibraltar and many other routes are rapidly moving away from pushing heavy steel. Pushing heavy steel through the water takes a lot of energy and fuel. Just as the airlines are trimming weight from their aircraft so too are ship owners advised to leave ashore all that is not needed. Not only spare parts, stores, water, fuel, oil, etc being trimmed to just enough to complete the journey in safety, even crew facilities are best provided on the dock. They should take their breaks during turnarounds rather than disappear to cabins through the journey. On the question of crew, fast ships leave the off-watch ashore so that only the working crew are carried. This means that accommodation for crew is not required on the ship, just the minimum crew facilities, like on an aircraft. Catering is therefore much less in demand as only the passengers and working crew have to be fed. The shorter the journey, the less the catering demand. All these points lower the weight of the ship still further, and lower the kilowatts required to drive the ship at the required speed. Fast turnarounds and good shore facilities are required to save fuel. Every minute saved in berthing and turning around the ship is a minute available at lower power on the crossing. On the other hand slow turnarounds have to be made up by higher passage speeds at greater fuel burn. Incat THE Magazine Issue 36 7
Page 1: FUEL ECONOMY & HIGH SPEED CRAFT www
Page 4 and 5: 4 Incat THE Magazine Issue 36
Page 8 and 9: Fast Ferry Benefits Slow + Extra =
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Page 12 and 13: A Smoother, Cleaner Bottom! Captain
Page 14 and 15: Building Aluminium High Performance
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