Whether it is a jacket, a monopile or an abandoned platform, there are many structures offshore that need to be marked for a limited period of time. Examples are jackets waiting to have the topside installed or to be removed, platforms that have been abandoned and are waiting for actual decommissioning or monopiles waiting for transition pieces or met masts to be installed.
Since 2013 we have marked all of the above mentioned structures and therefor have a broad experience.
This blog aims to provide a few suggestions to make the decision on what to use on such structures a bit less complicated, by going through a number of steps.
1. Regulations
In general all regulations need to be met to avoid issues with the authorities. However, in case the marking is required for a very short period, deviations from the regulations sometimes are accepted. For example, in the UK 10 nm mile main lights have been accepted under certain circumstances, whereas the regulations specify a 15 nm main light with a 10 nm backup light. Temporary marking of structures need to be reviewed case by case and when a deviation does not result in an increased risk of an accident, it might be possible to get approval for a system that is smaller and cheaper than what would be required in accordance with the regulations. There are however situations in which it is hard to meet the regulations, eg for a single jacket, with limited space and in case of platform decommissioning, most likely a weak spider deck in the splash zone.
2. ATEX vs Safe Area
The majority of the temporary markings will be for safe area, since temporary markings typically are required on structures that are classified as safe areas. Of course there are exceptions, and temporary marking of hazardous areas is more complicated. And far more expensive. Most operational platforms are considered to be completely hazardous areas, but for temporary marking, it is very cost-efficient to see if there are spots on the platform that are: a) actually safe area and b) suitable for installing temporary Aids to Navigation systems.
3. Type of structure
Each type of structure provides its own limitations and opportunities. The design of the skid for a monopile will differ from the design of skids for a platform. The way the skids are installed on the structure differs, depending on type of structure and preferences of the client. However, it does not matter if the structure is a monopile, a jacket or a platform, the regulations state that they are marked in basically the same way. Only offshore windfarms are marked differently, with the exception of the sub-station.
4. Power supply
For short term marking, a relatively small system using primary cells typically is a good solution. Of course, after the job is done, batteries need to be replaced for a possible next job, but by avoiding using PV modules, the skid can be made much smaller and total costs are lower. In particular for one-off projects, this is an interesting option to consider.
For long term marking, PV modules are the most reliable and cost-efficient solution. I know companies have tried to use small wind turbines, but the results that I am aware off, are really disappointing. I know of turbines that actually have been blown off the platform.
According to a couple of clients of mine, who made a comparisson between small wind turbines and PV modules, the performance of the turbines was poor. The main reason, favourable wind conditions are not as regular as one might think, very often there is too little wind, or – and this may come as a surprise – too much.
PV modules generate power every single day, even when it is cloudy. Output will fluctuate largely over a year, but it is far more predictable than windpower, for example by using NASA data, as we do.
For temporary Aids to Navigation, keep things simple. Gelled lead-acid batteries are reliable and relatively cheap and you do not use an MPPT or very complicated charge controller to get a very well performing solution.
I once was asked to design a system with top notch PV modules (300Wp or more) and Ni-Cad batteries. I informed the client that this would not be a very good idea, as it would be far more expensive, far more complicated and less reliable than what we usually would design. They insisted on receiving a proposal, and when I sumitted it, with an alternative proposal using our standard solution, it took them less then 15 minutes to decide using our standard lead-acid batteries.
Just keep in mind: you do not need PV modules with a very high Wp, neither as you need the highest quality batteries: you just need to make sure that a handful of lanterns, a fog signal, a visbility detector and maybe an AOL, AIS or remote monitoring system needs to be powered all year round. Selecting the right mix, with very low power consumption and high reliability, allows you to keep the system simple and lean.
On the other hand, autonomy is a very important issue. The standard 96 hour autonomy that typically is required for AtoN installations, is not sufficient for a system that uses PV modules to charge the batteries. Be on the safe side, and add some more, because you want the system to continue to operate for at least 2 weeks even if your worst case scenario becomes reality. Spending a few dollars more on PV modules and batteries always will beat arranging a emergency and unscheduled maintenance trip.
5. Skid design
Obviously, the design of the skid depends entirely on the type of structure, the duration of use, which season the skid is used, and most importantly, the power consumption of the users. Regardless of the size of the skid or the number of skids in use, one thing is vital to me: they need to be strong in order to withstand lifting, gael force winds and the salty environment of the sea. And they need to be as compact as possible, in order to allow for (relatively) easy shipping over land and in a supply boat. And of course, we need to take into account the lifting capacity of the cranes to be used. Other things to consider are ease of commissioning and of decommissioning.

6. Aids to Navigation
In general, local regulations specify what Aids to Navigation are required, which may differ per country. For all projects we have been involved in, there is one common theme: the lack of a main power supply. We rely on a number of solar panels and a pretty hefty battery pack to keep the system up and running all year round, so reduction of power consumption is absolutely vital.
Typically Morse U flashing marine lanterns are required on the corners of the structure, however, on a monopile or jacket, a single lantern may be sufficient. A fog horn might be required, in which case it is good practice to add a visibility sensor as well, in order to avoid the fog horn sounding 24/7, which consumes a lot of power (relatively). From a certain elevation above Mean Sea Level, Aviation Obstruction Lights (AOL) will be required. An AIS transceiver and remote monitoring is recommended and most clients will require the latter for sure.
As mentioned earlier, in particular the marking of a jacket of which the topside already is removed and which will be removed itself within a reasonable time frame, may be problematic to mark in accordance with the regulation. I will dedicate a separate blog to this topic.
As per today, we have supplied AtoN systems for over 15 platforms, 2 monopiles, and 5 jackets (Offshore wind and Oil/gas). Each platform requires its own approach, its own design, which we achieve by offering a modular system, which can easily be customized. Final design is always in very close cooperation with the client. And we would be more than happy to help finding a suitable solution for your structures as well.