Good day everyone
I would like to bring one issue for your attention which I had recently to deal with. Let’s imagine typical power and propulsion configuration for DP2 vessel as below:
4 x DG, 4 independent BUSes for each A,B,C,D)
2x Stern Azimuths
3x Bow Tunnel Thrusters
We have the following setting during DP operations:
Now, my doubt is that someone has established on ASOG 45% of load as the limit for Azimuths to turn the status to Yellow which is reasonable as one Azimuth would take 90% of load in case if other one fails, that should still allow to bring the vessel to the safe location.
The question is why the relevant limits on three tunnels are set to only 30% of load on ASOG? I still try to figure out the right explanation to this and I was even in a bit of arguing with other SDPO’s (this is exactly third vessel where I see this). Some of those questioned were not able to give me any answer that would make a sense for me, someone said that 90%:2 is 45% for Azimuths then 90%:3 is 30% for Tunnels which is an answer I can’t accept.
What I insist is that as per CAMO/ASOG we have to consider always worst single failure which could be a fail of any tunnel too. In other words I would consider the limit on tunnels of 60%, not only 30% if we have this case analogical to stern propulsion.
Your comments will be much appreciated.