In-deph|In-depth | RESEARCH & DEVELOPMENT RESEARCH & DEVELOPMENT
Speed loss due to added resistance in
wind and waves
Professor Kwon* presents an extension to the original approximate
formulae, developed by Dr R L Townsin and the author in 1983, to include
block coefficient (C ) 0.55 – 0.85 and Froude Number (F ) 0.05- 0.30.
B n
T
he weather formulae used in this resistance due to waves. This has been worker rather than the practioner and
paper are based on interpretations continually reported and discussed by the reference 1 is only applicable for the case
of detailed calculations of speed Seakeeping and Performance Committees of block coefficients C =0.62, F =0.25 and
B n
loss due to wind (van Berlekom: Ref 2), of the International Towing Tank C =0.8, F =0.15. Moreover, reading values
B n
motions (Maruo: Ref 3), and wave reflection Conferences (ITTC) in 1978 (15th) and off a scale on the graphs in reference 6 is
resistance (Kwon: Ref 4). These methods 1981 (16th). One of the main reasons for still not very convenient to use and the
have been recommended in ISO 15016 the inaccuracy is that most conventional calculations of added wave resistance in
(Ref 5). Some comparisons are presented, methods hardly take account of the oblique seas inspire less confidence than
for series 60 hullforms, between the results accurate added wave resistance caused head sea calculations.
of the new proposed approximate formulae by wave diffraction and reflection, which The purpose of this paper is to provide
and the ones of detailed calculation as is nonlinear in nature. Another difficult a simpler and easier way to estimate the
shown in Fig 1. The results of the formula problem is that estimating the added effect of wind and waves over a wider
were also compared with some published wave resistance is too complicated to use range of parameters as follows:
model test data (Takahashi et al: Ref 9) practically, as shown in Fig 1. To solve the
•
Extending Townsin-Kwon’s approximate
full-scale data (Aertssen: Ref 8). The above mentioned problems the author formulae (Ref 1) to include block
comparison revealed that the formula has presented both methods for the first coefficients (C ) from 0.55 to 0.85
B
provides a good approximation for problem (Ref 4) and with Dr Townsin
•
Extending Townsin-Kwon’s approximate
practical purposes. the second problem (Ref 1 and Ref 6). formulae (Ref 1) including Froude
The methods in references 4 and 6 have number (F ) from 0.05 to 0.30
n
Introduction recently been recommended by the ISO
There are a number of reasons for 15016 guidelines (Ref 5). However, the Approximate formulae
determining speed loss at sea due to method presented in reference 4 is a The formulae are intended to provide
weather, for example: computer-based one using NAG library an estimate of the percentage speed loss
•
To analyse sea trial data routine and is still the tool of the research in bad weather when that weather is
•
To improve estimation of a service
power margin
•
To determine accurate optimum speed
for fuel economy
•
To improve performance descriptions
in connection with chartered party
conditions
The added resistance due to wind
may be readily estimated on the basis of
coefficients derived from wind tunnel
tests or inverted ship model tests in a
towing tank. For example, van Berlekom,
(Ref 2) provides a good account of
these procedures together with worked
examples.
Unfortunately, it is difficult to
determine acceptable values of the added
*Y J Kwon, MSc, PhD, FRINA, School of Naval Architec-
ture and Ocean Engineering, University of Ulsan, Republic
of Korea
14 The Naval Architect March 2008
NA Mar 08 - p14+15+
16.indd 14 10/03/2008 11:58:33
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 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100