Trans RINA, Vol 153, Part A4, Intl J Maritime Eng, Oct-Dec 2011


drydocking capacity discussed in the next section of this paper.


6.3 DRYDOCKING INFRASTRUCTURE


An assessment has been made of drydock capacity for Panamax and larger ships,


in terms of number of


drydocks (floating and graving docks) available for repair in 2011 [18]. A total of 550 drydocks capable of stemming panamax vessels or larger has been analysed10. The distribution of dock width is shown in figure 7.


China Sea


Atlantic Ocean


Mediterranean Indian Ocean


Total no. Drydocks 197


147 97


Pacific 44 Japan Sea Baltic Sea Black Sea


Arabian Sea Great Lakes Arctic Ocean


55 36


39 19 5 2 2


Panamax


Post- panamax


39% 61% 56%


44%


67% 33% 49% 51% 50%


50%


39% 61% 72% 28% 53% 47% 20% 80% 50% 50% 50%


50% Table 10: distribution of larger drydocks by region Figure 7: Distribution of dock width over 32m


“Conventional” panamax docks can be seen on the steepest part of the curve, between 32m and 40m. A minimum of 1m clearance either side of the ship would normally be regarded as the requirement for working space around the ship, although ships can be “squeezed” into docks if necessary. It can be seen from Figure 7 that a ship requiring a drydock greater than 40m width (that is for a ship greater than about 38m beam) the available docking capacity


is around 40% less than for


conventional panamax vessels and for a beam of 43m (requiring 45m dock width) the available dock capacity is halved.


Restriction of dock capacity will have an impact on drydocking costs. An enlarged Panamax vessel will be committed to competing for dock space with much larger, and for the shipyard more lucrative, ships. The revenue that a shipyard can earn per day of dock occupancy will typically be 10% to 25% higher for a large tanker (aframax, suezmax, VLCC) when compared to a large bulk carrier (Panamax or Capesize). Shipyards will inevitably choose the higher value vessels where available and the competitive position of the bulk carrier will be weakened.


Analysis of docking capacity by region, Table 10, suggests that the issue will be greatest for ships operating in the Baltic Sea and Mediterranean. For ships confined to those waters the availability of capacity for drydocking above Panamax size is limited and increase of


beam above 32.2m should be very carefully


10 Docks over 180m length and 32m width have been included in this analysis.


©2011: The Royal Institution of Naval Architects


If these values are compared to Capesize vessels, where no such constraints apply, then corresponding ratios of between 6.0 to 6.5 for L/B and 2.5 to 3.2 for B/T are


A-221 7. DESIGN IMPLICATIONS 7.1 DIMENSIONS AND KEY RATIOS


Removal of the beam constraint will clearly allow naval architects more freedom in choice of key dimensional ratios for vessels around the limiting size. The existing Panama Canal beam and draught constraints limit


the


design deadweight for dry bulk carriers to around 80,000 to 85,000 tonnes. To achieve the displacement required for vessels approaching this limit, length has to be increased resulting in a length to breadth ratio, L/B, of typically 6.75 to 7.1. For a beam of 32.2m this results in a length between perpendiculars of typically around 225 to 229 m. This is well within the length constraint set by the existing Panamax limits


but is


stability and strength considerations. The required displacement is also achieved by maximising block coefficient, CB.


constraints the breadth to draft ratio, B/T, is typically 2.2 to 2.7.


For dry-dock designers the decision on what beam limitation to set depends on the type of dry-dock. For steel floating docks where the design life would typically be expected to be around thirty years (although much older docks remain in use) the maintenance of


existing Panamax capability could be justified, given the likely persistence of Panamax ships in the fleet for the next twenty five to thirty years at least. For graving docks, however, where the design life will typically be expected to be between fifty and one hundred years, the existing Panamax constraint may be regarded as obsolete and New Panamax dimensions are more appropriate for dock design.


considered. For vessels trading East, on the other hand, and in particular trading within the vicinity of China, the limitations are slight.


the


constrained by In keeping with the beam and draught


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