Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014


In equation (4), WSA has been used. Volume2/3 could have been used instead. It is an observation only.


The authors have stated at the beginning of the paper that results have been compared with other published data. Apart from mentioning one or two references, I do not see any other published data in any of produced in the paper.


the figures


Finally, while the transverse separation (S/L) is of greater application in designing vessels with multi hulls, the longitudinal stagger (R/L) may not be so in case of a catamaran.


However, outriggers) could investigations.


AUTHOR’S RESPONSE The authors wish to thank the discussers for their comments and questions. Some questions were raised because we could not include all specific details and explanations concerning the subject


investigation of the


symmetrical catamarans clearances and staggers.


resistance components with


variations in hull


We are grateful to Prof A F Molland, Prof P K Sahoo and Dr A K Dev for their questions and corrections to our subject.


Reply to the comment of Professor A F Molland 1/


The size of model tested is considered to be relatively small in order to avoid the occurrence of blockage effect throughout the testing. The models were fitted with turbulence stimulation comprising sand grain strips of 0.5mm diameter and 10mm width. The strips were situated at leading edge about 5%LBP aft of the bow [15].


The model design derived from a modern ship hull and it does not taken from published generic family. Anyhow, the model tested was almost the same as the NPL model as described below:


Table 1. Rasio Geometri of models Catamaran Hull Form Cb L/V1/3 L/B B/T Present Study NPL 4a


0.573 0.397


7.16 10.73 7.40 10.40


kC C VF (3)


In the case of catamaran hull, as in [18] summarized a calm-water-resistance investigation into high speed semi- displacement catamarans, with symmetrical hull forms based on experimental work carried out at the University of Southampton. Two interference effects contributing to the total resistance effect were established; these are viscous and wave interferences. The total resistance of a catamaran could be expressed by the equation:


Ck C TC 1 AT     CF W (4)


1.58 1.50


Staggered hull configuration provides small resistance at Froude numbers 0.4 - 0:55, so this advantage of the configuration can be considered in practical ship design to improve the resistance performances. It should be known that the staggered hull configuration has a style that is not the same drag in the longitudinal direction for each hull and this can lead to change the turning moment


B-110


The factor ø has been introduced to take account of the pressure-field change around the demihulls and σ takes account of the velocity augmentation between the hulls and would be calculated from an integration of the local frictional resistance over the wetted surface, while (1+k) is the form factor for the demihull in isolation. For practical solution in a complex engineering at that point in time, ø and σ can be combined into a viscous interference factor β where (1+øk) σ = (1+βk). Hence


CkC TC 1 AT    CF W  can be calculated from the equation: ©2014: The Royal Institution of Naval Architects (5)


longitudinal stagger in case of a trimaran (monohull with two


interesting


both lateral separation and be


for further


that must be corrected appropriately and accurately by the steering (rudder) due to differences sway and yaw forces on each hull.


Reply to the comment of Professor P K Sahoo


Series of tests on models give the impression that several clearance and stagger positions were tested.


Then the subjects of CF and CW for demihull and catamaran can be described as follows: Reference [16] and [17] introduced the resistance into three components which is


an important


method: skin friction (CF), form effect on skin friction (CF0), and wave making


improvement resistances


CC C CW TF FO   where FOF, hence: CkC


of experimental of


CkC CTF W 1  (2)


It is now well known that the frictional resistance coefficient CF derived from a flat plate is not the same as that of the hull and, furthermore, that CF is only a part of the viscous-resistance coefficient CV. In order to improve the Froude method, it has been suggested that the ratio is independent of the Reynolds number Re and Froude number Fr, where k is the form factor.


over Froude's (CW). These


resistance components can be written with the following equation as:


(1)


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