11 Applications of an Oil Drift and Fate Model for Fairway Design
397
11.5.4 Economical Aspects of Fairway Design
The performance of shipping operations is measured in terms of the voyage speed
and fuel consumption. Evaluations of alternative fairway designs provide estimates
for the economical gain of applying seasonal or combined designs depending on a
particular ship and metocean conditions. To stay close to reality, a medium range
tanker Torm Ragnhild with a length of 183 m, a deadweight of 46,187 tons and
maximum and average speed of 15.2 and 13.8 knots, respectively, was selected to
evaluate the above-described fairways. Torm Ragnhild is a typical tanker for the
Baltic Sea that is suitable for sailing through the relatively shallow Danish Straits.
Its draught (12.247 m) is too deep for some of the shallow passages in the Gulf
of Finland and some of the fairways calculated above were slightly modified (the
cruises were moved offshore in the vicinity of some islands and peninsula).
Geography plays an important role for route evaluations in relatively small water
bodies with strong demands for coastal navigation. The Gulf of Finland is a characteristic example with rather steep coasts in the south-west, shallower waters in
the east and an archipelago at the northern coast. As a rule of thumb, depths less
than 100 m affect the tankers’ resistance and have to be taken into consideration.
The ship propulsion model calculates stronger resistances for shallower water. The
ultimate limit for the water depth is the vessels draught. Cruises along the shallower
northern shores of the gulf are subject to stronger sea bed interactions and ship hull
resistances than the southern cruises. This aspect has not been considered during the
fairway design above but it most likely affects the economical performance.
The analysis presented here is based on the annual mean wind, wave and current
fields that were used to specify weather and sea conditions. Seasonal variations, although of strong consequence for the maritime transportation were not taken into
consideration. The ship routing analysis is based on three years of mean wind, wave
and current data (1992–1994). The data has been used for pollution transport studies
before (Sects. 11.4 and 11.6), but it has been averaged over time for the economical
evaluations. Fairways of different designs are compared with each other according
to their departure/destination harbour. East and west going routes are analysed together. The focus lies on the fuel consumption and the average speed, which have
been studied under conditions of either fixed planning speed or fixed travel time.
The total consumption and speed are dependent on the preset calm water speed and
the metocean conditions. For Torm Ragnhild with an average velocity of 13.8 knots,
a calm water speed of 13 knots was selected. Under conditions of deep water, low
winds, insignificant waves and zero currents, the calm water speed is equal to the
velocity of the tanker. Under realistic conditions, the speed is often lower because
winds, waves and shallow water add to the resistance.
The economical gain associated with the relocation of existing fairways has been
estimated by cross-performance analysis. The existing routes and new designs have
been evaluated together, which allows performance assessment under equal conditions (Table 11.3). The existing routes favour transport from the main harbour in the
Gulf of Finland region, Saint Petersburg. The economical benefit of employing alternative routes in terms of fuel consumption and travel time will therefore be minimal
397
11.5.4 Economical Aspects of Fairway Design
The performance of shipping operations is measured in terms of the voyage speed
and fuel consumption. Evaluations of alternative fairway designs provide estimates
for the economical gain of applying seasonal or combined designs depending on a
particular ship and metocean conditions. To stay close to reality, a medium range
tanker Torm Ragnhild with a length of 183 m, a deadweight of 46,187 tons and
maximum and average speed of 15.2 and 13.8 knots, respectively, was selected to
evaluate the above-described fairways. Torm Ragnhild is a typical tanker for the
Baltic Sea that is suitable for sailing through the relatively shallow Danish Straits.
Its draught (12.247 m) is too deep for some of the shallow passages in the Gulf
of Finland and some of the fairways calculated above were slightly modified (the
cruises were moved offshore in the vicinity of some islands and peninsula).
Geography plays an important role for route evaluations in relatively small water
bodies with strong demands for coastal navigation. The Gulf of Finland is a characteristic example with rather steep coasts in the south-west, shallower waters in
the east and an archipelago at the northern coast. As a rule of thumb, depths less
than 100 m affect the tankers’ resistance and have to be taken into consideration.
The ship propulsion model calculates stronger resistances for shallower water. The
ultimate limit for the water depth is the vessels draught. Cruises along the shallower
northern shores of the gulf are subject to stronger sea bed interactions and ship hull
resistances than the southern cruises. This aspect has not been considered during the
fairway design above but it most likely affects the economical performance.
The analysis presented here is based on the annual mean wind, wave and current
fields that were used to specify weather and sea conditions. Seasonal variations, although of strong consequence for the maritime transportation were not taken into
consideration. The ship routing analysis is based on three years of mean wind, wave
and current data (1992–1994). The data has been used for pollution transport studies
before (Sects. 11.4 and 11.6), but it has been averaged over time for the economical
evaluations. Fairways of different designs are compared with each other according
to their departure/destination harbour. East and west going routes are analysed together. The focus lies on the fuel consumption and the average speed, which have
been studied under conditions of either fixed planning speed or fixed travel time.
The total consumption and speed are dependent on the preset calm water speed and
the metocean conditions. For Torm Ragnhild with an average velocity of 13.8 knots,
a calm water speed of 13 knots was selected. Under conditions of deep water, low
winds, insignificant waves and zero currents, the calm water speed is equal to the
velocity of the tanker. Under realistic conditions, the speed is often lower because
winds, waves and shallow water add to the resistance.
The economical gain associated with the relocation of existing fairways has been
estimated by cross-performance analysis. The existing routes and new designs have
been evaluated together, which allows performance assessment under equal conditions (Table 11.3). The existing routes favour transport from the main harbour in the
Gulf of Finland region, Saint Petersburg. The economical benefit of employing alternative routes in terms of fuel consumption and travel time will therefore be minimal