Hi Phil, just to update you, as you suggested I contacted the owner and received a prompt reply. However from his feedback this area is not as clear cut as I had imagined, apart from the boats sailing on one day and returning on their expected day, it seems of the various other anomalies effecting the patrol is down to how one interprets these. The criteria of what constitutes an individual patrol from another by identifying the reasons and time limits that impact it are listed accordingly, so then each individual boats sailings are assessed equally. Regards John