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depending on each fishing station depth. Catch sampling is carried out while the
vessel moves from one fishing station to the next one.
Surveys always start and finish at the port of Lisbon and last around 28 days.
Until now, at the beginning of the survey, the skipper decides whether to start
sampling, the northern half of the coast or the southern one, depending on the
current weather conditions, and in each case, the sequence of fishing stations to
be visited. All fishing operations must be carried out during daytime (from 7 am
to 6 pm). If the vessel arrives at a fishing station after 6 pm and before 7 am, it
should wait. Consequently, during the night the vessel just navigates from the
last fishing station of the day to the first fishing station of the next day. This
routine goes on for 7 days, after which the vessel must enter a port. The vessel
must arrive at one of the ports by 6 pm and leaves it the next morning, in order
to arrive at the first fishing station just before 7 am. After 14 days of survey, the
vessel has to anchor at the port of Lisbon where it stays for at least 24 hours
for food and water supply and to change research staff. The second part of the
survey is similar to the first one, covering the fishing stations that remain to be
sampled. All the above time conditions define the sets of time windows that will
be assigned to the fishing stations and to the ports.
As input we have a set of 95 fishing stations (mandatory cities) and 4 ports
(selective cities) namely Lisboa (Lis), Portimao (Portim), Figueira da Foz (Fig)
and Matosinhos (Matos). For each fishing station and each port we know the
latitude, longitude and depth. Travel times do not verify the triangle inequality,
since the ship has to circumvent the coastline, and might not be symmetric due
to the ocean currents. We have a forecast of the time spent in fishing operation
at each station, which depends on the respective depth.
Different weather conditions, met along the journey, lead to different vessel
speeds: Very nice weather conditions - the vessel speed is about 20 km/h (
11 knots); good weather conditions - the vessel speed is about 17 km/h (
9 knots); not so nice weather conditions - the vessel speed is about 14 km/h
(
8 knots).
Moreover, our partners from IPMA asked us to evaluate the impact on the
overall fishing operation time resulting from the purchase of new equipment.
It can be expected that new equipment reduces the extra time spent at each
fishing station by half,
:Set
= 30, for current equipment; set
= 15, for
new equipment. By combining all the above cases, we have considered six sce-
narios. Following the skipper directives, problem DSR has been decomposed
into two subproblems, each subproblem being a TSPSNTW. One subproblem
includes the South and South-West fishing stations (43) and ports Portim and
Lis (2). The other subproblem includes the North fishing stations (52) and ports
Fig,MatosandLis(3).
The information, that is available from previous years, shows that each sub-
problem has a feasible solution, under the weather conditions mentioned above.
Thus, the main objective is to save fuel. However, everyone on board wants to
return home as soon as possible. In order to mimic the weights of these two
concerns we set
λ
1
=2and
λ
2
= 1 in the objective function (1).
