Effect of the Minimum Ballast Condition on Bulk Carrier Manoeuvrability

Transcription

1 A part of BMT in Maritime Transport Effect of the Minimum Ballast Condition on for INTERCARGO ADDITIONAL SCENARIOS ISSUE DATE: 17 th December 2008 REPORT NO: C RA

2 CONTENTS 1 TERMS OF REFERENCE ADDITIONAL SCENARIOS SIMULATION RESULTS CONCLUSIONS... 3 APPENDIX A SIMULATION RESULTS... 5 Document Information Project Report Title Client Report ref: Effect of the Minimum Ballast Condition on - Additional Scenarios INTERCARGO C RA Prepared by: Mr Dimitrios Argyros Naval Architect, BMT SeaTech Ltd Approved by: Mr Simon Burnay Group Manager Marine Safety & Compliance, BMT SeaTech Ltd Document History Version Changes By 1 Draft for Release DA, SB 2 Final following client comments SB Information contained in this document is commercial-in-confidence and should not be transmitted to a third party without prior written agreement of BMT SeaTech Ltd. Copyright BMT SeaTech Ltd Report No: C RA

3 1 TERMS OF REFERENCE BMT SeaTech Ltd (BMT) was instructed by INTERCARGO to conduct a simulation study to assess the effect on ship manoeuvrability of minimum ballast conditions for Capesize bulk carriers. The results of this study are presented in BMT SeaTech Report C R of 19 th September Following presentation of the results to INTERCARGO s technical committee (CASTEC), it was requested that a number of additional scenarios be conducted to assist in further establishing the risk profile of the minimum ballast loading condition. This report summarises these additional results and is presented as an Addendum to the original report, which describes the methodology adopted for this project. 2 ADDITIONAL SCENARIOS The following additional scenarios were conducted: a) Runs and T6 were re-run with the loss of one tug during the swinging manoeuvre. b) Runs M7 and M10 were re-run with the loss of one tug during the swinging manoeuvre. c) Runs and T6 were re-run with a squall arriving during the approach channel transit. The squall consisted of a 35 knot wind from 110 degrees, which was chosen arbitrarily to present a challenging condition from the ship-handling perspective (wind on the stern quarter). d) Two new runs (A1 and A2) were conducted to assess the effect of the minimum ballast condition on the ability of the vessel to anchor safely. The squall conditions were also applied in this scenario. 3 SIMULATION RESULTS The full sets of simulation results for these scenarios are presented in Appendix A. The same indices used in the original report were used again to assess the differences between the manoeuvring capabilities of the typical Capesize bulk carrier in the Normal Ballast and Minimum Ballast conditions. In addition, for the anchoring scenarios, an index was defined as follows Anchor Index: i ( 10 * T ) CHAIN A =.(i) MAX ( TCHAIN) Where T CHAIN and T CHAIN MAX are the actual and maximum chain tensions (i.e. Maximum Breaking Load) respectively. Table 3.1 presents the summary results for the simulations performed. The equivalent index figures from the original study are presented in brackets alongside the new results. 2 Report No: C RA

4 Run ID Loading Condition Maximum Sustained Ship Index (i S ) Maximum Sustained Tug Index (i T ) (Tug) Normal Ballast 5 () (0.75) T6 (Tug) Min Ballast () () M7 (Tug) M10 (Tug) (squall) T6 (squall) Normal Ballast 0 (0) (0.75) Min Ballast 2.4 () 5 (0.5) Normal Ballast () (0.75) Min Ballast () () Comments Generally higher tug index than original during whole runs. Ship index equal to zero for M7 as rudder not used throughout. Higher values than original. Generally higher tug index than original during whole runs. Table 3.1 Summary of Results For scenarios A1 and A2 the key results are as follows in Table 3.2: Run ID Loading Condition No. of Dragging Occurrences Maximum Anchor Index (i A ) A1 Normal Ballast (-) A2 Min Ballast (-) Comments Normal ballast vessel is affected more by current hence drags more with similar chain tensions. Table 3.2 Summary of Results for A1 & A2 4 CONCLUSIONS Based on the analysis completed for this study, we can draw the following conclusions: Tug Failure: (i) For the scenarios where a tug failure is simulated, the tug index is unsurprisingly, higher when compared to the original run. The remaining tugs have to work considerably harder (mostly at 100% or zero reserve power) and perhaps more importantly, careful use of the tugs (in respect of positioning and use of lines or pushing) is required in order to try and overcome the shortage of tug power. (ii) In the case of the Ponto de Madeira scenarios, an additional tug was available (4 instead of 3 for Tubarao) and this helped to enable some redundancy, but as expected, the remaining tugs had to work harder and with less reserve power. (iii) (iv) For the Tubarao scenarios, the minimum ballast condition presents a significantly more challenging case for safe berthing in the event of a tug failure. For the Ponto de Madeira case, the situation is somewhat reversed (as per the original study), due to the ability to use the stronger current to aid the berthing manoeuvre. However, it was necessary to use a large burst of power and helm 3 Report No: C RA

5 to maintain control at certain points, but this was generally not sustained for a long period of time. Squalls: (v) (vi) (vii) Anchoring: (viii) (ix) The effect of the squall was to rapidly and strongly increase the power required to maintain course in the approach channel and tug power required to berth the vessel. In both loading conditions, it was very challenging to berth the ships safely and several attempts were necessary. Consequently, the tug index in both cases was higher than the original scenarios and it can be seen that the minimum ballast condition vessel had to make heavy use of the main engine and helm to overcome some of the tug power shortage. The minimum ballast condition presents the ship-handler with a significant challenge in the event of a wind squall due to the increased windage. The risk of an incident occurring must therefore increase accordingly and careful planning and extensive pilot and tug master training would be required to mitigate this risk. In both loading conditions, the anchors held quite satisfactorily in general and the dragging that did occur was relatively short lived and easily overcome, with very little or no drift of the ship s position. The normal ballast condition actually experienced more dragging occurrences and had similar chain tensions to the minimum ballast condition. This is due to the relative balance of wind and current forces. 4 Report No: C RA

6 APPENDIX A SIMULATION RESULTS 5 Report No: C RA

7 - Tug 1 Tug 2 Tug T6 T6 Tug 1 T6 Tug 2 T6 Tug 3 INTERCARGO Runs and T6 with one Tug Lost Wind 20kts, 30 deg, current 1 kt, 225 deg WIND: 20kts Current: 1kt 10kts Figure A5T: Track Plots for Runs & T6 with One Tug Lost ROT with Manoeuvring Safety Index ROT [ /min] 0 T6 Safety Index Figure A6T(a): ROT Plots for Runs & T6 with one Tug Lost Tug with Figure A6T(b): Safety Index for Runs & T6 with one Tug Lost Tug with Figure A6T(c): Tug Index for Run with one Tug Lost Figure A6T(d): Tug Index for Run T6 with one Tug Lost 6 Report No: C RA

8 :00:00 00:07:12 00:14:24 00:21:36 00:28:48 00:36:00 00:43:12 00:50: :00:00 00:07:12 00:14:24 00:21:36 00:28:48 00:36:00 00:43:12 00:50:24 - M7 Tug 1 M7 Tug 2 M7 Tug 3 M7 Tug 4 M7 M10 00:00:00 00:07:12 00:14:24 00:21:36 00:28:48 00:36:00 00:43:12 00:50: :00:00 00:07:12 00:14:24 00:21:36 00:28:48 00:36:00 - M10 Tug 1 M10 Tug 2 M10 Tug 3 M10 Tug 4 M7 M10 INTERCARGO Runs M7 and M10: Wind 15kts, 90 deg, current 2 kt, 000 deg with One Tug Lost Current: 2kts 10kts WIND: 15kts Figure A13T: Track Plots for Runs M7 & M10 with One Tug Lost ROT with Manoeuvring Safety Index ROT [ /min] Safety Index Figure A12T(a): ROT Plots for Runs M7 & 10 with One Tug Lost Tug with Figure A12T(b): Safety Index for Runs M7 & M10 with One Tug Lost Tug with Figure A12T(c): Tug Index for Run M7 with One Tug Lost Figure A12T(d): Tug Index for Run M10 with One Tug Lost 7 Report No: C RA

9 Runs and T6 with Squall (35 knots from 110 deg) Wind 20kts, 30 deg, current 1 kt, 225 deg WIND: kts Current: 1kt 10kts Figure A5S: Track Plots for Runs & T6 with Squall ROT with Manoeuvring Safety Index ROT [ /min] 0 T6 Safety Index T Figure A6S(a): ROT Plots for Runs & T6 with Squall Tug with - Figure A6S(b): Safety Index for Runs & T6 with Squall Tug with Tug 1 Tug 2 T6 Tug 1 T6 Tug 2 T6 Tug 3 Tug Figure A6S(c): Tug Index for Run with Squall Figure A6S(d): Tug Index for Run T6 Squall 8 Report No: C RA

10 Runs A1 and A2 with Squall (35 knots from 110 deg) Wind 20kts, 30 deg, current 1 kt, 225 deg WIND: kts Current: 1kt 10kts Figure A1: Track Plots for Runs A1 & A2 with Squall Dragging Occurences 1 Dragging (1= Yes) Min Ballast Light Arr 0 00:00:00 00:28:48 00:57:36 01:26:24 01:55:12 02:24:00 02:52:48 03:21:36 [h:mm:ss] Figure A2S(a): Dragging Plot for Runs A1 & A2 (incl. Squall) Chain Tension Index Chain Tension Index (10*Actual/Max) Min Ballast Light Arr :00:00 00:28:48 00:57:36 01:26:24 01:55:12 02:24:00 02:52:48 03:21:36 [h:mm:ss] Figure A2S(b): Anchor Index Plot for Runs A1 & A2 (incl. Squall) 9 Report No: C RA