Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
T T
CC k C CC k C
WCAT [(1 ) WDEMI [(1
) F CAT ] F DEMI ]
(3)
The authors conclude that the form factor, for practical purposes, is independent of speed and should, thus, be kept constant over the speed range. This was a good practical solution to a complex engineering problem at that point in time. This is an explanation as to why this mathematical formulation has been used.
In Equation (4), WSA has been used. Volume2/3 could have been used instead. It is an observation only.
Area and displacement ratio can be written as: wetted surface m
Area and Displacement ratio Displacement m
( () 2 32/3
This ratio is one of the measurements of the wetted surface area as it relates the displaced volume it contains. This ship can take a bigger resistance that other ship even though both have the same wetted surface. This ratio is useful only in conjunction with other hydrostatic indicators, for example, a sphere.
A work has been carried out regarding the staggered demihull configuration by Söding [14], Sahoo
et.al. [13] and Caprio
et.al. [19]. While the staggered catamaran hull form is not immediately practical, it is of great interest to understand the wave field interaction between the demihulls. Söding [14] confirmed the results of the numerical investigation on the staggered catamaran and highlighted a reduction of up to 50 % of total resistance with a 50 % LWL stagger for Fn = 0.4. Then Sahoo et al [13]
reported computation
their experimental and numerical results that a significant reduction in
resistance could be achieved by finding the optimum position of the stagger, which confirms the conclusions arrived at by Söding [14]. Further experimental work needs to be carried out over a wide range of hull forms to ascertain the effectiveness of resistance reduction due to the staggering of the demihulls. Caprio
at.al [19] on their experimental data obtained
potentiality of stagger configuration. It has been measured resistance reductions up to 30 % vs. symmetric catamaran. The following figure show Staggered Catamaran Efficiency Factor (λ) for length-displacement ratio L/∇1/3 = 5.74 for hull spacing S/L= 0.3.
The present study also shows a similar trend with the Caprio’s result. The present study obtain a smaller value of staggered catamaran efficiency factor because present study used a model with larger length-displacement ratio of L/∇1/3 = 7.16.
Staggered Catamaran Efficiency Factor (λ) of model L/∇1/3 = 5.74 [19]
REFERENCES
12. SAHOO P K, SALAS M and SCHWETZ A (2007); Practical Evaluation of Resistance of High-Speed Catamaran Hull Forms-Part I, Proc. of the Journal of Ships and Offshore Structures Volume 2, No 4, pp 307-324.
13. SAHOO P K, DOCTORS L J and PRETLOVE L (2006); CFD Prediction of the Wave Resistance of a catamaran with Staggered Demihulls, Proc.
of the 14. SÖDING, H. 1st International
Conference on Marine Hydrodynamics (MAHY 2006), Visakhapatnam, India, 5-7 January.
(1997), Drastic Resistance
Reductions in catamarans by Staggered Hulls, Proc. Fourth International Conference on Fast Sea
Transportation (FAST ’97), Sydney, Australia, Vol. 1, pp 225-230, July
15. ITTC 2002, Recommended Procedures and Guidelines, Model Manufacture: Ship Models, ITTC 7.5-01 -01-01, 2002
16. HUGHES G, “Friction and form resistance in turbulent flow, and a proposed formulation for use in model and ship correlation”, Transactions of RINA, Vol. 96, 1954.
17. HUGHES G, “An analysis of ship model resistance into viscous and wave components”, Transactions of RINA, Vol. 108, 1966.
18. highlights the great
INSEL M and MOLLAND A. F, “An investigation into the resistance components of high speed is placement catamarans” RINA Transactions, Vol.134, 1992.
19. CAPRIO F and PENSA C. “Experimental
Investigation on Two Displacement Catamarans: Systematic Variation of Displacement, Clearance and Stagger”, International Journal of Small Craft Technology, RINA, 2007.
B-112
©2014: The Royal Institution of Naval Architects
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