Hi there!

For my final these i need to model an arrival schema for a vessel. This schema consists of certain periods. These periods then consist of four events. So these four events (one period) occur in a cycle, making an arrival schema for a whole season.

One of the four events out of a period is the time spend 'at sea'. The duration of this event is determined by the minimum value out of five different variables; limited days staff can stay at sea (T1), time the bait stock lasts per trip (T2), chance of bad weather (T3), chance of red tide (T4), and the maximum numer of sea-days allowed per vessel per season (T5).

I find it hard to model the duration of the chance of bad weather and the duration of the chance of red tide. This is how far I came..

The chance of bad weather is 3 times per year, and when this happens it lasts for approximately 4 days. So the change per day is 3*4/365=0,0329.

The time at sea per period is, lets say, 30days. (in the model this is determined by the minimum value of T1 and T2, but for now lets set it to 30days)
So the change that bad weather occurs in a certain period is : 0,0329*30=0,9863.

This is where I get stuck. Now that I know the change per period, how can I check if this actually occurs? And if this occurs on which day?

I previously modelled the day by RAND()*30. And to see wether this occurs I previously modeled it with =IF(RAND()<="Chance of bad weather per period, so 0,9863",RAND()30,40) (40 since this will always be the biggest value)
But since RAND() always chooses values between 0 and 1, with this formula it says that almost every period bad weather occurs..

Thanks in advance!!