Studies show that most accidents happen during the night[25] especially around 4 am due to the Circadian rhythm of humans.[2] Studies like Project Horizon[26] have recently been done to analyse which factors cause this fatigue. The lack of sleep and quality of the sleep are two of the main issues. The lack of sleep is due to the long hours that the workers (especially the Officers) have to do (work weeks of 70 hours +).[4] After that there is the quality of their sleep which is affected by lots of different factors.[26] There will be the quality of the food on board, the vibrations due to the engine and waves, the noise of repair or works or engine, only naps (not sleeping 8 hours in a single run but 2 or 3 naps a day) because of the watch system and secondary jobs.