In this post we’re going to look at bringing the foundations to the installation vessel at site. It’s thought that, as with carrying more components, we can increase the working time by transiting less. If another vessel (a barge and tugs) brings components to the main vessel the transit requirements are reduced, although it’s worth noting that offshore transfers of this type are quite strictly limited; the trade-off between transit reduction and sensitive operations is the main concern here.
Our base case simulation includes the transfer of installation components to the installation vessel from a storage barge in the port. This analysis moves this process to the site location. To do this is simply a case of allowing the Loading Cycle group to inherit its location from the Foundation Installation group. It’s worth noting that the barge will start and end the analysis at site with this setup (as this is the location of the first and last task it is used on). This is an assumption we’re reasonably happy with at this point, although if we wanted to we could add mobilisation and demobilisation type tasks in the port to force this. We’re also, at this point, not going to worry about resupplying the barge. Instead we’ll assume that there are sufficient barges available to always be ready to resupply the installation vessel, we’ll also assume that an appropriate loading strategy has been determined to allow this.
In our changes to the flow diagram we haven’t modified any of the durations or limits which are applied to the loading tasks. Instead we’ll set up the barge vessel so that it’s station keeping and access ability sufficiently limits work. The applied limits are shown below and are 1.5m significant wave height and 12m/s wind speed. This puts a severe restriction on the loading tasks, and if anything these limits, particularly the wave height, may be optimistic.
Transit and port access limits have also been set.
Let’s take a look at the results; oh dear! Shown below is the project progress burn up and we can see that after 1 whole year of operating less than two-thirds of the foundations are complete. Let’s adjust the x-axis limit.
Below is the burn up chart with the x-axis modified to allow the entire installation to be seen. With these changes the operation is taking between 500 and 600 days in most cases. This is terrible and not an installation approach we would be overly keen to use. The reduction in installation vessel transits does not improve the performance because the offshore transfer of components between moored vessels is so strictly limited. Let’s discard this option entirely.
The Next Steps
We’ve seen throughout this series of posts options we have to enhance our installation performance, these being:
- Avoid working in the winter months, we need to somehow get the installation completed in the spring and summer as this is when our progress is fastest, however we need this to be one summer season, not a split installation.
- Increase the carrying capacity of the vessel so that we spend less time transiting and more time installing when favourable conditions occur. We’ve also seen that trying to achieve the same result by using an offshore transfer is not viable.
In the next post we’ll explore these points further and consider what happens if we use two vessels rather than the one we’ve allowed ourselves so far.