Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014 DISCUSSION
EXPERIMENTAL INVESTIGATION OF THE RESISTANCE COMPONENTS OF SYMMETRICAL CATAMARANS WITH VARIATIONS IN HULL CLEARANCES AND STAGGERS
A Jamaluddin, Indonesian Hydrodynamics Laboratory, Surabaya, Indonesia, I K A P Utama and W D Aryawan, Dept. of Naval Architecture & Shipbuilding Eng., ITS, Surabaya – Indonesia and B Widodo, Dept. of Mathematics, ITS, Surabaya, Indonesia (Vol 154, Part B1, 2012)
COMMENT
Professor A F Molland The paper provides some useful experimental data on the effects
of hull resistance.
The models tested are relatively small. Would the authors please describe the turbulence stimulation used? Also, were the models derived from a published generic family?
The influence of separation of the hulls on resistance would seem to show the same trends as published data. These show favourable interactions for some separations and unfavourable for others, depending on speed.
Some combinations of stagger and speed show decreases in resistance. This seems to be particularly the case for the Froude number range Fr = 0.40-0.55. Do the authors consider that stagger could be incorporated in a practical ship design in order to take advantage of such resistance improvements?
If stagger were incorporated in the
design, would asymmetry in (longitudinal) drag, and a turning moment, be expected due to asymmetry of the interaction effects? If so, might the use of rudder to correct such turning, with resulting drag, negate some of the advantages of the stagger?
Professor P K Sahoo
The authors are to be congratulated on bringing out a relevant paper which will be of considerable interest to the naval architecture community. The paper deals with the current problem of increasing efficiency, has practical relevance and will be of interest to practicing naval architects and designers.
I would like to know details of the mathematical equation: viscous part of equation (1) and that of equation (2). When the is multiplied with (1 + k); has been equated to ; but it has not been mathematically explained why .1 has been taken again equal to 1 instead dropping . This needs an explanation as to why this mathematical formulation has been used by the authors.
It is noted that in section 4.3 authors are illustrating the effect of R/L (stagger ratio) on the resistance but have used S/L parameter in text. Also in equation 6 IFclearance is the ratio between CTCAT and 2*CTDH (where CTDH is the total resistance of one demihull in isolation)
The conclusion drawn by the authors in paragraph 4 of the CONCLUSION is not consistent with the figures 6 and 7. In fact it would appear that beyond Fr 0.55, the stagger ratio has negligible or no influence in reduction in resistance.
Attention is drawn to earlier contributions made by others as shown in the following references:
Dr A K Dev
The authors should be congratulated on a wonderful work on a subject, which is of a great interest for catamaran type vessels in terms of resistance phenomena like interference effects. Though similar works are carried by others, such investigations do establish a fact that the designers can rely on with greater accuracy.
separation and stagger on catamaran
In several places it has been mentioned that ‘series of tests on models’ has been carried out. This would give the impression that several models were tested when in fact only one model with several clearance and stagger positions was tested. In equation (2) it would be appropriate to write CF and CW as those for demihulls and this students.
equation has created confusion amongst
When we have a catamaran with staggered demihulls the effective length is now more than L (1.2L, 1.3L and 1.4L in this paper) and this will affect the Froude Number (Fr). It appears that this has not been considered and it is suggested that volumetric Froude Number be used to
overcome this problem Fn
g 1/3 V .
Table 3 shows the various form factors at different clearance and stagger positions. It would have been interesting to see the changes if authors would have calculated the form factors using equation 7 shown in [12].
©2014: The Royal Institution of Naval Architects
B-109
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88