The ‘Medium’ type O&M activities are postponed 73% (on
average) due to OAV ‘Mobilisation’ (Fig. 4). OAVs cannot perform
repairs during the night shift, so ‘Shift’ has the second highest
proportion in the total ‘Medium’ failure downtime by 13%. OAV has
better capability, so ‘Weather’ is not a major issue for the OAV. Due
to the fact that the hazard rate of the ‘Medium’ failures is relatively
lower, the number of simultaneous failures is also lower; therefore
it is unlikely to postpone repairs due to lack of ‘Resource’. Similar
to ‘Manual reset’ and ‘Minor’ failures, ‘Repairs’ have a very minor
contribution to the total downtime of the ‘Medium’ failures.
In order to ascertain higher accuracy in the results, downtime
regarding jack-up vessel has to be investigated in detail. In this
respect, the downtime is grouped under ‘Purchase’ and ‘Fix on fail’
strategies. Due to the fact that ‘Mobilisation’ is ‘0’ for the ‘Purchase’
option, ‘Repairs’, ‘Weather’, and ‘Resource’ comprise all the downtime.
With regard to ‘Purchase’ strategy, ‘Repairs’, ‘Weather’,
‘Resource’ account for 27%, 24%, 49% (on average) of the total
‘Major’ failure downtime, respectively. With regard to ‘Fix on fail’
strategy, the ‘Mobilisation’ is the main cause of the downtime by
88% on average.
Fig. 5 shows the distribution of total costs associated with each
‘Transportation type’. Charter cost, fuel cost and technician cost
account for 54%, 2% and 44% of the total CTV associated costs,
respectively. With respect to helicopter, charter cost has the
largest contribution by 77%, while fuel cost and technician cost
contribute by 13% and 10%. In the OAV related operations,
mobilisation cost, charter cost, fuel cost and technician cost
account for 40%, 51%, 2% and 7% of the total OAV costs, respectively.
On average, the charter cost of the jack-up vessel dominates the
jack-up vessel associated costs by 84%, while mobilisation cost,
fuel cost and technician cost contribute by 13%, 1%, 2%, respectively.
However, the jack-up vessel charter cost and the mobilisation
cost have significant uncertainty; therefore, these aspects are
demonstrated in detail, categorised under ‘Purchase’ and ‘Fix on
fail’ strategies. For ‘Purchase’ strategy, the cost of vessel is
significantly higher; on the other hand, the mobilisation cost is
‘0’. When the ‘Charter length’ values for the ‘Fix on fail’ strategy are
increased, the total charter costs increase proportionally to the
number of days that the vessel is chartered. On the other hand, the
mobilisation costs decreases, because when the jack-up vessel is
chartered for longer period, the number of failures that can be
repaired in a single charter period increases; thus the number of
charters, and eventually the number of mobilisation operations
decrease.
Fig. 6 demonstrates the distribution of total O&M costs. The
graph on the left hand side shows the total O&M cost per unit
power production (d/MWh), whilst the graph on the right hand
side shows the total O&M cost spent within 5 years (simulation
period). Cost per unit power production is a well-known criterion
to assess the performance of the O&M activities; on the other
hand, it is also important to identify the actual costs that operators
have to finance. In this context, the total direct O&M cost consist of
staff costs, OEM costs, fixed costs, and transport costs. The total
O&M costs are calculated by considering the lost revenue and the
total direct O&M costs. It can be seen that the staff, the OEM, and
the fixed costs show significantly low uncertainty, on the other
hand the transport costs and the lost revenue have higher
uncertainty. On average, the staff, OEM, fixed, transport costs
and lost revenue account for 7%, 9%, 13%, 38%, and 33% of the total
O&M costs, respectively.
Considering all the information above, the best and the worst
O&M planning configurations are listed in Tables 11 and 12,
respectively. The variables in Tables 11 and 12 are represented
by the designated values as in Table 10 for presentation purposes.
In these tables the rankings of the configurations are identified
from the total O&M cost/production, since this output considers
total O&M cost and total power production, and therefore shows
the cost effectiveness of the O&M strategy.
As shown in Tables 11 and 12, the best configurations include
helicopter with ‘750’ and ‘1000’ contract hours; on the contrary,
helicopter is not considered in the worst configurations, which
shows the importance of the helicopter within the O&M fleet. The
daily charter rate of the OAV is relatively higher; on the other hand
the production loss and the revenue loss due to OAV unavailability
are more significant. Therefore, the OAV is chartered ‘21’ days or
longer in the best configurations. The ‘Fix on Fail’ strategy is
identified as the most and the worst cost-effective jack-up vessel
chartering strategy, but the charter length varies in the configurations.
The best jack-up vessel charter length is ‘14’ days; because,
the failures associated with the jack-up vessel occur less frequently,
so chartering the jack-up vessel for a longer period
increases the revenue loss significantly, which is not compensated
by the power production increase. From availability point of view,
3% improvement can be expected. Moreover, the total O&M cost
can be decreased by 24% (from 36.64 d/MWh to 27.71 d/MWh) by
selecting the most favourable plan for the O&M fleet and associated
activities. Therefore, the financial and operational aspects
are improved through the implementation of the methodology