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4.2.6.2 Observation of the current environmental situation 
In Process 5.2.1, it is in principle solely the information resulting from visual observation which is suitable 
as input information. This is not therefore represented. In the case of Process 5.2.2 (“Observe weather 
data”) a distinction should be made between three different time references: 
• Local reference: observance of the current weather, based on visual information (not repre 
sented), measured temperature, air pressure, etc. 
• “Medium range”: medium-term time reference, i.e. forecast of the weather to be expected for 
the next few hours/days. For example used as a decision basis for planning an evasion route 
for bad weather regions. 
• Global reference: weather data or long-term forecasts concerning the whole planned voyage. 
DFD 5.2.3 models the determination process of the present current, i.e. direction and speed of the bod 
ies of water surrounding the ship. In mathematical terms, these variables are obtained from the differ 
ence between the ship movement through the water (STWx, CTWx) and the ship movement over 
ground (SMGz, CMGx). Since the movement over ground in particular is not available every time, 
moreover, an optional second way should be stated for the approximate determination of these vari 
ables from current and tide information (e.g. from current atlas, tide tables, empirical values). The result 
of the process is the present current according to amount (drift) and direction (set). 
DFD 5.2.4 contains the measurement of the apparent wind (i.e. the resultant from true wind - calculated 
on a static co-ordinate system - and voyage wind). The true wind is thus obtained by taking into account 
the speed of the ship over ground. For the purpose of conversion, further information is used. By way 
of result, the process supplies the true and apparent wind according to amount and direction. 
DFD 5.2: Observation of the current environmental situation