Calculation settings

Different calculations for the same request

To make a calculation the operator selects a series of settings that are to be used during the calculation. With these settings he can make different advices for the same request. Typically several calculations are made and then a choice is made which outcome is most suited for the voyage. All the different options are listed below.

Safety criterion: Calculation setting

The safety criterion is determined by the selection of a Calculation setting. This setting is not just a single figure, but determines the type of calculation, the precision, cut off values, et cetera, for each part of the voyage. The following list of properties are set:

Time location granularity	The initial step size in the time location diagram. This step size is used in the root finding algorithm to find the times that a safe situation changes to not safe or vice versa.
Time location precision	The final precision roots are sought within the granularity.
Preferred route width	The first possible route with the preferred width is found. If none is possible the width will iteratively be reduced by 50% (with a minimum of the time location granularity) until a route is possible or no route is found at all.
Number of draws per time location point	To determine the safety of a time / location the monte carlo simulation varies in water level, wave height, swell height and water speed/direction. This setting determines the number of iterations in the simulation.
Reliability	The simulation results in a distribution of UKC / bottom touch probability. Assuming a normal distribution, the reliability determines which cut off value is used to decide if a time / location is safe.
Number of wave spectra to select	In the vertical motion analysis each combination of Hm0/He10 values is analyzed by selecting this number of wave spectra.
Wave direction mean	A profile of vertical motions is built by varying the wave impact direction. The range of variation is determined by a normal distribution around a mean direction.
Wave direction standard deviation	The standard deviation used in varying the wave impact direction.
Number wave direction iterations	The number of iterations the wave wave impact direction is varied.
Wave direction spread	The spread variable of the wave direction passed to OCTOPUS. A spread of 8 is typical for swell.
Damp current factor inside harbor	It is assumed that the current is less inside the harbor then in the open sea. This factor determines the amount the current should be damped inside the harbor. With a value of 1 (or 100%) the current is damped in full.
Damp waves factor inside harbor	It is assumed that the wave and swell height is less inside the harbor then in the open sea. This factor determines the amount the waves should be damped inside the harbor. With a value of 1 (or 100%) the waves are damped in full.
Kilometer position to start damping	Depending on the harbor layout this position determines at which kilometer position the damping (current and waves) should start. Al positions with a kilometer position smaller than this figure will have less current and waves.
Cut off steps	A list of safety cut off values per kilometer and draft interval. For each interval the following cut off values are given: Minimum relative UKC: the minimum amount of UKC one should have as a fraction of the ship draft Minimum absolute UKC: the minimum amount of absolute UKC one should have Minimum relative UKC and squat: the minimum amount of UKC one should have after squat reduction as a fraction of the ship draft Minimum absolute UKC and squat: the minimum amount of absolute UKC one should have after squat reduction Maximum route bottom touch probability: the maximum (average) probability to touch the bottom for a channel voyage Maximum route segment bottom touch probability: the maximum probability to touch the bottom at any point during the channel voyage The relative UKC criteria should have an incorporated margin for prediction errors. The absolute UKC and probability criteria use the reliability setting (listed above) as an extra margin to incorporate prediction errors, which is not used by the relative UKC criteria.
Cross current exclusions	A list of cross current exclusions per draft interval.

Speed regime

A speed regime gives the speed over the ground for each kilometer interval of a channel voyage. Typically the speeds are higher at the beginning of the channel (open sea) and lower near the berth. During the calculation the speed is adjusted for current to find the ships heading and speed through the water, which are relevant for the squat and motion analysis.

Use of manual prediction overrides

Via a manual prediction module, an operator has the possibility to override prediction data. This can be necessary when certain data is evidently wrong or when the operator has extra knowledge which is not incorporated in the predictions that are imported from MATROOS. After entering the overrides the operator can choose to make calculations with or without the overrides. This gives insight in the effect of the edits.

Use of channel bottom elevations

PROTIDE uses the nautical guaranteed depth of the channel. It can happen that at some times at some locations the channel is not deep enough. These locations are listed in the channel bottom elevations. By selecting the option to use this list, the calculation will take the elevations into account.

Delayed departure time

By default PROTIDE finds the first possible route after the requested departure time within the next 24 hours. Via the Delayed departure time option an operator can try to find a route at a different time. By entering a date and time PROTIDE will find the first route in the time window 24 hours after this date.