Two of the model ships had two superstructures, while two had one superstructure. The remaining two model ships had no superstructures.

Part of the study was to check the validity of using Finite Element methods for such structures and part of the study was to determine the effect of superstructures on model ships.

The study showed that the Finite Element method was most suitable for the analyses of such structures. It also showed that superstructures do strengthen ships, but do not change their resonant frequencies appreciably.

The longitudinal strength and vibration of ships is of much importance in marine studies and many studies have been made on them [1,2,3,4,5,6,7] over a number of years.

In this paper, a theoretical and an experimental study has been made on the effect of superstructures on the longitudinal strength and vibration of 6 ship models. The models are shown in Figure 230.1, where it can be seen that there are two families of models. Models 2, 3 & 4 had 3 decks. Models 1, 5 & 6 had 2 decks. Models 3 & 6 had no superstructures. Models 1 & 5 had one superstructure. Models 2 & 4 had two superstructures. The superstructures on Models 4 & 5 had sloping transverse and longitudinal external bulkheads. The superstructures on Models 1 & 2 had vertical external bulkheads.

It should be emphasized that the adoption of external sloping bulkheads is popular with modern day warships as they help such vessels to be less vulnerable to missile attack. All 6 models were constructed in Polymethyl Methacrylate. (PMMA or 'Perspex').

Figure 230.1: Ship Models 1 to 6.

Model 1: Single superstructure Model 2: Double superstructure Model 3: No superstructure Model 4: double, inclined superstructure Model 5: Single, inclined superstructure Model 6: No superstructure

1

Muckle, W., Strength of Ships Structures, Edward Arnold Ltd., London, 1967.

2

Muckle, W., The Design of Aluminum Alloy Ships Structures, Hutchinson, London,1963.

3

Rossell, H.E. and Chapman, L.B., Principles of Naval Architecture, Vols. 1 & 2, SNAME, Jersey City, USA, 1958.

4

Mackney, M.D.A. and Ross, Carl T.F., Superstructures Effectiveness in the Preliminary Assessment of the Hull Behavior, SNAME, J. Marine Technology, 36, 1, 1999.

5

Mackney, M.D.A. and Ross, Carl T.F., Preliminary Ship Design using One-and-Two-Dimensional Models, SNAME, J. Marine Technology, 36, 2, 1999

6

Smith, C.S. and Chalmers, D.W., Design of Ships Structures in Fibre-Reinforced Plastic, Trans. RINA, May 1987, pp. 45-62.

7

Brown, D.K., Naval Architecture, Naval Engineers Journal, Jan. 1993. doi:10.1111/j.1559-3584.1993.tb02705.x

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