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of 'macro wake' measurements for a wide range of ships, wide enough to cover a large part of the world's ship population.

TABLE I Overview of Data Sets

Data set no.

Cb

L/B

B/Ta

Prop.

Bulb

Loading

Speed m/s

Tankers

 

11

0.84

6.4

2.5

single

yes

full

1.3

12

0.79

6.4

4.7

single

yes

ballast

1.3

21

0.78

5.7

4.2

single

yes

full

1.3

22

0.76

5.7

5.1

single

yes

ballast

1.3

31

0.82

5.0

4.0

twin, inw.

yes

full

1.3

32

0.82

5.0

4.0

twin, outw.

yes

full

1.3

34

0.75

5.0

5.8

twin, outw.

yes

ballast

1.3

Containerships

 

41

0.69

7.1

2.8

single

yes

full

2.0

51

0.61

6.1

3.6

single

yes

full

2.0

61

0.62

5.4

3.7

twin, inw.

yes

trimmed

2.0

62

0.62

5.4

3.7

twin, outw.

yes

trimmed

2.0

64

0.62

5.4

3.7

twin, outw.

no

trimmed

2.0

Frigates *)

 

71

0.50

8.0

4.0

twin, inw.

no

full

2.0

81

0.44

7.3

3.2

single

no

full

2.0

*) A third frigate data set was obtained at DTRC in the U.S.A. [2]

With the term 'macro wake' we follow the terminology of [1] and it is used here with the intention to convey two things: i) that the measurements have not been restricted to the propeller disc area, as is the common practice in ship model testing, and ii) that the emphasis is on the detection of large scale features in the wake.

This paper starts with an overview of the scope of the investigation, i.e. the main characteristics of the ship models used, the kind and the extent of the measurements, etc. The description of the measuring devices and an error analysis follows in section 3. Subsequently, a summary is given of the main findings, extracted from a careful examination of the collected experimental data, in section 4. Closing remarks in section 5 complete the paper.

2.
Scope of investigation

Wake data were acquired for 8 ship models: 3 tankers, 3 container or auxiliary vessels and 2 frigates (complementary data for a third frigate were collected at DTRC [2]). The bodyplans of the hulls are shown in Fig.1. Each data set has an identification number of two digits of which the first refers to the hull geometry and the second to an operating condition. A change of operating condition is either a draft variation or a reversal of the direction of rotation of the propellers; in one case however a local bow form change is involved. Table I gives a summary. It is noted that each data set includes results with and without operating propeller(s). Moreover, additional measurements were carried out under data set 21 for the propelled hull in absence of the rudder.

The measurements comprised:

  • the three components of the velocity vector;

  • the six components of the Reynolds stress tensor;

  • longitudinal and transverse wave profiles.

The velocity and Reynolds stress measurements were made in several transverse planes. An overview of the number of planes and their position for each data set is given in Appendix I.



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