Hinged containership design concept

Is the hinge the answer for the ultra large container ship?

Although not a new idea, the concept of building a ship as two or more independent ship sections joined together by means of a hinge has never been fully explored or tried out. This is largely because the technology has not been up to the task combined with a reluctance by shipowners to build unproven designs. However, a ship?s engineer from Taiwan, Bill Wen Chang Huang, claims to have solved the problem by incorporating improvements to existing US patents and has now patented his ideas with the United States Patent.

Novel invention

The hinged ship concept is based on the principles of naval architecture which states that the maximum shear force of a ship?s length occurs at 1/4 and 3/4 of the hull length. The argument is that if two hulls are put together with a hinge linking them, then the bending moment is smaller than that of a solid hull of equal length. The two ship bodies are vertically pivotable and a few degree movement of the hinges can overcome the maximum bending moment that usually occurs on traditional container ships which have to endure about four times greater the stress and strain due to hogging and sagging. One can therefore, in theory, design a ship 50% larger in length and breadth while thinner steel plates can be used in the ship?s construction.

The point is not to build two small ships instead of one large one, for that would involve duplication of resources. Instead, this invention enables naval architects to push the boundaries beyond the present physical limitations imposed by the not inconsiderable shear force experienced in large vessels. A boxship measuring 500 metres long, with a beam of 70 metres, a 33 metre depth and a 12 metre draught with a hinge in the middle will have a maximum hinge shear force of 38,106 tonnes. The hinge can be designed to comprise of 60 sets of hinges each 90 cm wide with 10 cm thickness fan-shaped cover plates each side of the hull and on the ship?s bottom to shield the hinge from water as well as reduce disturbance of water flow due to the creation of the hinge part amidships. This hinge is much easier to manufacture than making the main engine bearings and crankshaft.

From the Comstock?s principles of naval architecture, one can assume that the speed is 25 knots. When comparing a 284 metre long ship with the proposed 500 metre hinged example, it can be calculated that the resistance of the longer ship is 2.16 times that of the 284 m vessel. The container carrying capacity of the larger vessel is 3.123 times greater so the unit container resistance of the 284 m ship is 1.442 times that of the 500 metre one. This represents a 44.2% saving of power and for a large container ship operator like Ever Green, the company would save an estimated $2.2 billion over 10 years.

Because the patented shaft hinge is located above the waterline, there will be very little corrosion or rust problems and the system should have a life of more than 20 years.

By disconnecting the two halves of the 500 metre vessel, the separate sections can be turned round in a 300 metre diameter turning basin while the 12 metre draught will enable the boxship to berth in any of the main ports of the world. There is also less chance that the propeller will get out of the water and ?race? so a larger propeller can be fitted to achieve greater efficiency.

This novel invention can be used for most ocean-going merchant vessels and tankers. Another example used by Huang is a traditional Cape size bulker of 289 metres by 45 metres wide that can be scaled up to 433 metres long with a 67.5 metre beam thus saving 25% fuel. Huang is also proposing to use air cushion air outlets in the shape of small air compressors which can boost fuel saving to 35%. He cites as an example a 395 metre container ship with a 50 metre beam, a depth of 24.2 metre to compete with a standard container ship. This will save 25% on fuel and if one adds 75 sets of 3hp air compressors and air cushion air outlets, fuel saving can be up to 35%. Without the patented hinge, this size of ship would need a 36.3 metre depth which requires 12,000 tonnes more steel to build and 10,000 tonnes more ballast to obtain the stability. In contrast, the hinge system would only require 1,200 tonnes of steel.

Huang also claims that existing vessels can be modified and fitted with hinges to increase carrying capacity since he alleges that the hinge is simple to fabricate and would have a huge impact on the shipping industry.

Conclusion

The principal objective of the invention is to provide a novel ship design where the ship is constructed in at least two separate ship bodies linked to each other by means of a huge horizontally installed hinge. This will permit the upward as well as the downward angular motion of one ship body relative to the other. The bending moment on such a hinged ship is only a quarter of that on a conventional ship of comparable dimensions and, when the hinged vessel ploughs into the waves, the flexible hinge allows the ship to absorb a portion of the force of the waves and minimizes the hogging and sagging.

Another objective of the invention is to enable the ship sections to be readily attached or detached from one another so that when approaching a small harbour or quay, the hinged ship can be taken apart thus facilitating berthing.

If compared with conventional vessels of the same structural strength, the hinged ship can be made larger which means ship holds become larger, less engine power and smaller propellers are needed consequently resulting in less fuel as well as material cost. n

l The ?inventor? of the improved hinge patent is: Bill Wen Chang Huang, Taipei Hsien, Taiwan.

Tel/fax: +886 2 229 63245