1、 o” in smaller vessels, small differences in the consumables could have a significant effect on the loading conditions and exchange sequence suitability. Flow through exchange In some specific casesflow through exchange may be more attractive than sequential exchange for double hull tankers. Using t
2、heflow through method eliminates the concerns of shallow forward and aft drafts, and extreme trims. While it may take somewhat longer to carry out, there is less total “attention time” than with the sequential method, especially when sets of tanks are simultaneously overflowed. 10 ABS Advisory Notes
3、 on Ballast Water Exchange Procedures STD-ABS 3B-ENGL 11999 m Ob53302 00252211 b59 m Double Hull Tankers Ship Type Volume capacity of ballast tanks (m3) Time to perform flow through exchange (hours) 40,900 DWT 12,900 32 Suezmax A Listed below are key findings arising from the ballast waterflow throu
4、gh exchange analysis of double hull tankers: 55.000 27 Applying theflow through method does not alter the stability, stress, and ship attitude. While it typically takes longer to carry out than sequential exchange, the process requires less “attention time” from the ships personnel. Suezmax (C) Doub
5、le hull VLCCs, with cargo and ballast tanks arranged five long within the cargo block, have difficulty with sequential exchange. For these vessels, flow through is an attractive al temative. 74,400 46 Bulk Carriers VLCC Single Hull Three typical bulk carriers were investigated for sequential and flo
6、w through ballast exchange. These included a Handysize, Panamax, and Capesize. These ships are arranged with upper and lower hopper ballast tanks, and each design has one midships cargo hold fitted to carry ballast. 105.000 44 Listed below are key findings arising from the ballast water management a
7、nalysis of bulk carriers. Sequences for the bulk carriers are quite complex, requiring many steps to maintain drafts and longitudinal strength within acceptable limits. Safe application of these sequences will require careful monitoring by the ships crew. Bending moments approach the 100% allowable
8、value for each of the bulk carrier exchange sequences. These ships were not designed to have ballast tanks emptied during the course of the voyage and, therefore, careful planning is necessary to ensure that bending moments are maintained within acceptable levels. For all designs, it is difficult to
9、 exchange ballast in the cargo hold while maintaining compliance with forward draft, shear force and bending moment criteria. The cargo holds are generally not designed to withstand loads induced by resonant sloshing experienced during partial filling conditions. This precludes exchanging ballast in
10、 the holds during severe weather conditions. ABS Advisory Notes on Ballast Water Exchange Procedures 11 STD=ABS 18-ENGL 1999 = Ob51102 0025222 595 Bulk Carriers Ship Type - Ballast condition Handysize - Light Ballast - Heavy Ballast Panamax -Normal Ballast - Heavy Ballast Capesize - Light Ballast -
11、Normal Ballast Sequential exchange Time to perform exchange sequence (hours) Additional time to ballast to original drafts (hours) 27 2 40 9 17 29 6 11 36 4 44 8 Bulk carriers are similar to tankers in that they are frequently in “ballast only” conditions. Normal and Heavy sequences were evaluated f
12、or each bulk carrier. Partial load conditions were not investigated. The total time involved in the ballast exchange process is as follows: Table 7 0 Sequences are relatively complex as draft forward, draft aft, and bending moments frequently approach the limiting values. For the vessels investigate
13、d the sequences require between 12 and 19 independent steps, and up to 65 ballast movements. 0 It is difficult to concurrently maintain adequate propeller immersion and forward draft, 0 Capesize vessels generally have large double bottom ballast tanks extending two holds in length. It may not be pos
14、sible to exchange some ballast tanks when the cargo hold is filled with ballast water, as excessive shear forces are encountered. In situations where the hold is emptied, the drafts are greatly reduced to near those in the light ballast condition. Shear force values for all of the Heavy ballast cond
15、ition sequences that were studied are close to allowables. 0 The Panamax vessel is fitted with overboard valves in the upper hopper ballast tanks. This allows quick gravity discharge of the ballast, significantly reducing the sequence time and providing more flexibility in how the pumps are used. Fl
16、ow through exchange The flow through method eliminates concerns of exceeding shear force and bending moment limits. Flow through exchange is an attractive alternative to the sequential exchange for the Capesize heavy ballast condition; it eliminates the light draft problem associated with sequential
17、 exchange. 12 ABS Advisory Notes on Ballast Water Exchange Procedures STD-ABS LB-ENGL 1999 Ob5LL02 0025223 421 ship TYP Handy size Panamax Capesize The total time involved in the ballast exchange process, when performing operations in pairs of tanks, is as follows: Table 8 I Bulk Carriers I Volume c
18、apacity of I Time to perform flow ballast tanks (m? through exchange (hours) 17,200 46 32,300 50 69,700 45 Example of a sequential exchange procedure for a Handymax bulk carrier To illustrate the complexity of a sequential procedure the following is presented as an illustration of a procedure that w
19、as developed for a Handymax bulk carrier. This is a 28,000 DWT bulk carrier with 5 cargo holds and 5 P 5 - O - 5 5 1 (A - m IC 4- $ Sample Handymax bulk carrier ballast exchange sequence d90ION S Mi Z ON dMnZON S90EON d9EON SMnEON dMnEON saatoN d9PON SMnPON dMnPON SaaSON O 4 4 f O O O O r 8 4 4 z r
20、O O O O O r O 4 4 4 4 4 O O O O O O r a z r O 8 O z 4 o O O z O O z O O r O 4 O O r O 4 o 8 O r O O r O 4 4 4 8 4 o 4 o O O r O O O O O O r O O r O 4 4 4 O O O 4 4 4 4 O O O O O 8 r 5 O 4 o 4 4 O O O O O O O r O z o o 8 4 0 O O r O O O 4 o 4 4 O O O f O O - O 4 o 4 4 O O O O 4 8 O o z 4 4 0 O O O O
21、O 4 O O r O 0 4 O o O O 4 o 4 4 O O O O O O o 4 4 4 4 O O O O ABS Advisory Notes on Ballast Water Exchange Procedures 15 yeadaJoj s ao I ON d ao I. ON S Ml I .ON d Ml I ON S 90 Z ON d 80 Z ON 5 SMlZON U dMlZON S8aEON f dEON $ SMlEON m d Mfl E ON SaapON d9PON sMnPoN 0 dMlPON S90EON d Ea f ON S Ml C O
22、N d Ml 5 ON - al U O K 65 c 2 - i 3 I g 7 O 4 z o O O O O 7 O f 8 8 z r O O 6 ag I Sample Handymax bulk carrier ballast exchange sequence (continued) so 7 O O 4 O O r O o 8 7 O O O f O O O r O I Io Q T 16 ABS Advisory Notes on Ballast Water Exchange Procedures Sample Handymax bulk carrier ballast ex
23、change sequence (continued) yeadaiod s aa i ON d aa 1 ON SMn lON d M 1 ON s Ea z ON d aa I ON - i SMlZON E dMnZON U al c=i SEaCON 8 5 dEEON SMnEON m dMlEON U O r 5 2 S9PON Y 2 d9aPON 1 SMnPON m dMnPON II 3 SaaSON o d 80 S ON S M S ON O O O O - 8 F o z O ABS Advisory Notes on Ballast Water Exchange P
24、rocedures 17 STD-ABS 18-ENGL 1999 = 0651102 O025228 TO3 Containers hips Containerships rarely operate in “ballast only” conditions. A typical voyage may consist of ten or more port calls, with containers generally loaded and off-loaded at each port. Ballast is allocated during the course of the voya
25、ge to accommodate changes in the distribution of cargo and consumables, and in response to operational requirements such as draft limitations. For containerships the procedure is more of a “management plan” than a ballast exchange process. There are a number of sometimes-conflicting objectives facin
26、g the containership planner as containers are assigned to specific slots on the vessel. There is strong economic incentive to avoid re-handling of containers (i.e. moving containers to allow the cargo below to be off-loaded or shifting containers to adjust for trim or strength limitations). Stowage
27、preferences limit the planners ability to optimize with regard to trim, bending moments, and stability, and it is unlikely that container stowage could be significantly modified to facilitate ballast exchange. However, the fact that containerships retain cargo onboard throughout the voyage presents
28、some benefits with regard to ballast management. Some tanks may remain permanently empty; some tanks can be maintained permanently full with locked in ballast; and it may be possible to discharge other tanks at sea rather than in port. For a given trade, the quantities and weights of containers load
29、ed and off-loaded in each port generally follow repetitive and/ or cyclic trends. These historical data are used by planners to pre-plan stowage, and by ship Masters to aid in their decisions regarding allocation of ballast and consumables. By pre-planning an entire voyage cycle, it is expected that
30、 the amount of ballast moved and particularly the need to discharge ballast in port can be minimized. This study investigated the practicality of a ballast management approach that considers entire voyages for three containerships. The ships selected for this analysis include a 1200 TEU feedership o
31、perating between Northern Europe and the Mediterranean Sea; a 2500 TEU Panamax containership operating between the US. West Coast, Hawaii, and Japan; and a 4800 TEU Post-Panamax containership operating in the U.%-Far East trade. For each ship, the following investigations were carried out. DeveloDme
32、nt of voyage specific ballast water management approaches: A complete voyage cycle was developed using historical data from actual voyages for container weights and distributions, and other consumables. As far as practical, the actual ballast allocation scheme was also retained, although adjustments
33、 were made to eliminate the discharge of contaminated ballast in port or during inter-port legs through shallow waters. When allocating ballast, priority was given to maintaining compliance with the stability and strength regulations. An effort was also made to maintain the draft, trim, list, propel
34、ler immersion, and visibility within the acceptable limits. Within these constraints, ballast was allocated in order to minimize the amount of ballast to be discharged in port or coastal waters. When deballasting in port was unavoidable, the ballast was either originally loaded in deep ocean waters
35、or an exchange was carried out in deep water. 18 ABS Advisory Notes on Ballast Water Exchange Procedures STD-ABS 18-ENGL 1999 Ob51102 0025229 94T m Containerships Ship Type 1200 TEU - Feeder 2500 TEU - Panamax 4800 TEU - Post-Panamax Ballast movements for each vessel (voyage) are summarized in table
36、 10. Table 10 Total ballast movement during voyage (MT) port (MT) Ballast discharged while in 930 440 (Coastal Water) 10,600 3,700 (Deep Ocean) 11,100 O Containerships Ship Type 1200 TEU - Feeder 2500 TEU - Panamax 4800 TEU - Post-Panamax For the three voyages that were evaluated, effective ballast
37、water management procedures can be implemented with little impact on vessel operations. Nevertheless, it should be recognized that a containership loaded to its marks and approaching GM or bending moment limits will be unable to exchange ballast without exceeding allowables. Generally this will only
38、 impact Panamax and smaller vessels. The post-Panamax containerships have ample excess ballast, deadweight capacity, and stability margin to bring additional ballast onboard before initiating the exchange process. Maximum change to Maximum change hogging bending moment to GMt (m) 17% 0.52 10% 0.36 8
39、% 0.54 Impact of ballast water exchange on ship properties: To assess the ?worst case? scenario, each vessel was fully loaded to her summer loadline draft in such a way that both the GMt (actual GM equal to the required GM) and still-water bending moment (actual still-water bending moment equal to t
40、he permissible still-water bending moment) were at their limiting values. Each tank was run through an exchange sequence to determine the effect of the exchange on the drafts, trim, propeller immersion, static heel, still-water bending moments and shear forces, GMt, and bridge visibility. Containers
41、 were then removed from the upper-most tiers on deck until compliance with the stability and strength criteria could be maintained throughout the exchange process. To assess the impact of emptying and re-filling tanks, each ship was loaded to its loadline such that the GM equals the minimum permissi
42、ble, and the still-water hogging moment is at maximum permissible value. Then each tank or pair of tanks was run through an exchange cycle. The maximum changes to the stability and bending strength characteristics encountered during the exchange of any one tank or pair of tanks is displayed in table
43、 1 1 : Table li ABS Advisory Notes on Ballast Water Exchange Procedures 19 STD-ABS LB-ENGL L999 D Ob5L102 0025230 bbL Containerships Ship Type 1200 TEU - Feeder 2500 TEU - Panamax 4800 TEU - Post-Panamax reduction in GM, during the exchange of a tank or pair of tanks on the three vessels ranged from
44、 0.36 to 0.54 meters, and the increase in hogging moment ranged from 8% to 17% of the allowable. The table below provides values for the reductions in payload required to allow exchange of these tanks; if the initial load condition has the vessel fully loaded to her marks with stability and bending
45、moments at their limiting values. As illustrated in the analysis of the three containerships, such payload losses can generally be avoided as ballast can be “locked in” when a vessel is heavily loaded. Table 12 Reduced payload to account for change in bending moment 1474 MT I 17% B.M. change 345 MT
46、I 10% B.M. change 1965 MT 18% B.M. change Reduced payload to account for change in GM, 759 MT I 0.52m GM, change 950 MT 10.36m GM, change 930 MT l0.54m GM, change The 1200 TEU feedership does not have heeling tanks or other means for internally transferring ballast from side to side. Since ballast a
47、djustments are required to control list during cargo operations, there is no alternative but to discharge ballast in port, A substantial portion of the voyage for the 1200 TEU vessel studied involved inter-port transits through shallow waters.It was not possible to exchange ballast water in the deep
48、 ocean, resulting in unavoidable in-port discharge of coastal waters. With the exception of the above mentioned problem of controlling heel on the feedership, it was found that for the three voyages and ships analyzed, effective ballast water management procedures can be implemented with little impa
49、ct on vessel operations and with no loss of container payload. Through planning, the amount of ballast exchange can be minimized, as many tanks can be maintained either full or empty during the course of the voyage. In preparation of a port call, tanks can often be initially ballasted in the deep ocean, which further reduces the need for exchange. Slamming For the ballast exchange operations studied, it was common to have a decrease in forward draft during
