Trans RINA, Vol 154, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
Table 16: Estimated Block Coefficient for surveyed SESSF vessels Vessel
A
B 0.55 C
CB (Estimated) Froude Number Already has bulb installed 0.55
0.36 0.29
By adopting these steaming speed changes, an estimated fuel consumption reduction of 5% could be achieved.
Since all of the vessels surveyed have a speed greater than Froude number FN of 0.24 when steaming to their chosen fishing grounds, the addition of a bulbous bow may reduce the wave resistance of the vessel. Note that the wave making resistance
of a vessel increases faster than frictional
resistance between Froude Numbers of 0.27 and 0.36. However only vessel A that operates in the south eastern shark and scalefish fishery has a bulb installed. For an initial estimate on whether this modification would benefit any of the vessels surveyed, the block coefficients CB, the Froude number of vessel at different speeds and the estimated time spent at steaming speed and fishing time per year are summarised in Table 15.
The data in Table 15 and Table 16 respectively are then plotted on the graph shown in Figure 10.
0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32
0.50 0.60 Vessel B 0.70 0.80
Block Coefficent (Cb) Vessel C
Figure 11: Recommended Passive Fin Design [14]
Figure 10: Froude Number and Block Coefficient Range where a bulbous bow is of benefit [12]
From this initial estimate, only vessels B and C will benefit
amounts of operations.
from installing a bulb since they spend large time
steaming compared to fishing
An installation of an appropriately sized bulb will approximately reduce the resistance by 5 to 10% during
B-66
However, since working deck space is at a premium on small vessels, the retractable section of the fin support should be orientated vertically. The fins must also be located out of the path of the fishing gear that comes over the side of the vessel, such as craypots and long lines. Retractable fins also have the benefit of not creating any drag when they are not needed. To determine how much this occurs, the wave data for Tasmanian waters needs reviewing which is presented in Figure 12.
©2014: The Royal Institution of Naval Architects 0.90
Estimated 1170-2340
Steaming
Time (hrs/year) 4050
Estimated Fishing Time (hrs/year)
975 1199-3276
steaming to and from fishing grounds. Also there is a possible additional benefit of reducing pitching due to the additional water plane area in the fore wad section of the vessel.
Most of the vessels in this study (except rock lobster vessels C and D) had bilge keels fitted to the vessel to reduce roll motions. These roll reduction devices work by forming eddies around the fin structure as the vessel rolls which dissipates roll energy.
properly designed only increase the resistance of a vessel by 2 to 3% of hull appendage drag due to
An increase in skin friction due to an increase in wetted surface area
Interference drag at junction between bilge keel and hull
However, when these bilge keels are poorly designed, they tend not to be aligned with the flow around the vessel and can create large amounts of appendage drag. On some of the vessels surveyed, the
determination of the flow
visualisation/streamlines around the vessel bilges keels may not have been done at the initial design stage or during retrofitting.
The additional drag due to misaligned bilge
keels can increase fuel consumption by 10-15% (Helmore, 2001). This can be improved by replacing the bilge keels aboard the vessel with passive fin stabilizers similar to the arrangement shown in Figure 11.
resistance [13] by increasing
Bilge keels when
Froude Nmber
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