Settings / Tides
Settings SEAiq includes support for various forms of tidal data. It is always important to consider the source of your data. This is not intended as a complete description of tidal/current data. There are numerous references and other forms of documentation, including from the various data sources that SEAiq employs.
- Official/Unofficial data: Some of the tidal/current data is official and some is Unofficial.
- Online/Offline: Online data requires an internet connection in order to access. Offline predictions do not require an internet connection: they use so-called harmonic analysis to predict tide/current at particular times. There are numerous potential sources of error in tidal predictions. Note that real-time tidal data may also come from AIS broadcasts; this is similar to online data source but uses AIS over VHF broadcast and does not require internet connection.
- Reference/Subordinate Stations. For predictions, stations are divided into reference and subordinate stations. Reference stations have full harmonic analysis and may maintain permanent sensor on station. Subordinate stations are defined in terms of a reference station, typically with some time offsets, level offsets, and/or multipliers. All tidal predications should be taken with a grain of salt; this is particularly so in the case of subordinate stations because they are estimates of estimates.
Tidal predictions from NOAA and CHS may be downloaded in advance in order that they are available even when you are offline. When you choose to download the data, it downloads at least several weeks of data. This is the procedure for setting this up:
- Make sure you are connected to the internet.
- Create a VRM that includes all the stations you wish to download. This VRM should be in a fixed location, not attached to a vessel. You can create a VRM by (1) single tapping to select a center location, (2) double-tap a second location and choose Add Tool / Add VRM, (3) give your new VRM a descriptive name such as "Tidal VRM" so you know what it is for, (4) adjust the position of the VRM as needed.
- Choose Select Stations here and pick the VRM you just created.
- Press Update to download the data. This may take some time, depending on the number of stations in the VRM.
- When compilete, you can see how far in the future your predictions have been downloaded by viewing Status
- Periodically, you will want to Update your data to ensure you have needed predictions.
Settings The following settings control operation of tides and currents.
- Show Labels: Show labels for tide stations. Not all tide sources are supported.
- Use Fill for Labels: Show labels with solid background. This makes them easier to see, but may obscure other details.
- Track Nearby Tide Stations: (Only SEAiq Pilot) When enabled, this will determine the next and previous tide stations along your route. Own-Ship must be following a route. To be selected, a station must meet the following conditions:
- Within the Distance Threshold (see below) from the route.
- No more than 20NM from Own-Ship along the route.
- It must have a tide reading no more than 1 hour old.
- Distance Threshold: (Only SEAiq Pilot) This is the maximum distance a tide station may be from the current route to be automatically selected for Own-Ship. The default is 1NM.
- Interpolate Tide for Own-Ship: (Only SEAiq Pilot) When enabled, the water level at Own-Ship will be estimated using linear interpolation based on relative positions along the route. Please understand that interpolation is based on the closest position of the route to the station. If a station is past the end of a route then then interpolation is based on the end-point of the route. Important: Depending on conditions, linear interpolation may not be an accurate method to estimate tides. Knowledge of local conditions should be used to evaluate accuracy of estimates. The following conditions must hold for this to be enabled:
- Track Nearest Tide Stations must be enabled.
- A next and previous station must be identified.
- The times of most recent readings reported at the two stations must be no more than 15min apart.
- The two stations must report the same reference level.
- Dynamic Tidal Adjustment: (Only SEAiq Pilot) When enabled and a tidal value is present for the current position of Own-Ship, an adjustment will be made to chart display.
Alternately, a tide station can be opened and Select for Tide Adjustment pressed to manually select a tide station. This is disabled by pressing the disable (X) button in the status panel.
The tidal adjustment is applied globally to all charts based on the estimated value at Own-Ship's current position. Thus, viewing any chart showing water with different tidal levels will display erroneous data.
This has the similar effect as manually editing Settings / Bathymetry / Tidal Adjustment. Please refer to that documentation for more information.
When this feature is enabled, the tidal adjustment will be automatically updated (eliminating any prior value). When this feature is disabled, the tidal adjustment will be reset to 0 (regardless of any prior value).
Dynamic tidal adjustment is only used if the sensor data is no older than 15min.
Important: This feature must be used with care.
When the value is changed, it is rounded down (never up) to the next lowest 5cm value. The chart display will then only be changed when the current estimated level is less than the adjuste value or more than 10cm above it. This means the adjustment is (1) always less than the estimated water level and (2) is no more than 10cm less.
- Tide Sensor Timeout: (Only SEAiq Pilot) Maximum age for real-time tide data, after which the sensor data is colored red in the status bar an no longer used for dynamic tidal adjustment. The default is 15min.
Own-Ship Set & Drift (Advanced)
- Use Set & Drift in Own-Ship Predictions: (Only SEAiq Pilot) When enabled, a panel will be displayed with sliders for set and drift for current. This allows Own-Ship course predictions to account for set and drift, potentially increasing their accuracy. AIS targets are not affected. The set and drift are assumed to already be a component of Own-Ship's COG/SOG. This option only has an effect when the vessel turns; as the vessel turns the set and drift component will stay fixed but the remaining components will turn.
Enabling this feature disables the Trial Rate-of-Turn CHL feature.
- Set Follows Route: (Only SEAiq Pilot) When enabled along with Use Drift in Course Predictions and following a route, the bearing of the route closest to Own-Ship will be used for the set. This can be useful in rivers or other areas where drift is expected to roughly follow the direction of the route.
Note the set has a single fixed value for a particular position of Own-Ship at the current time and predicted movement of Own-Ship will not affect various course predictions. In other words predictions do not change set when, for instance, Own-Ship is following a curve.
- USA (NOAA) Online Tides/Currents: Enables downloading a list of NOAA tide and current stations. You can select a station to get a link to official online data.
NOAA indicates tidal current predictions as being in Beta.
This requires an internet connection. However, you can download predictions so that they are available when off-line.
- NOAA PORTS for Major Ports in USA: (Only SEAiq Pilot) Enables download and display of NOAA PORTS data for many ports in the USA. The stations are identified using red diamonds with P. An attempt is made to update the stations every 6 minutes.
- NOAA NBDC Buoy Data: Enables download of environmental data from NOAA National Buoy Data Center (NBDC) stations. The stations are located around the world, but most densely around the USA, England, and South Korea. The stations appear as yellow diamonds on the display, which can be selected and queried for their data. These are updated every 15 minutes when connected to the internet.
- Canada (CHS) Tides: (Only SEAiq Pilot) Enables downloading a list of CHS tide stations. You can select a station to get a link to official online data.
This requires an internet connection. However, you can download predictions so they are available when off-line.
- Canada SPINE Levels (CHS): (Only SEAiq Pilot) Enables periodic downloading of tide interpolations that CHS creates. These are made using the SPINE method, described by CHS as follows: "The service web de prévisions et d’interpolation des niveaux d’eau (water level forecast and interpolation web service -- also called SPINE) is a system allowing one to obtain water levels at any time on the St. Lawrence navigation channel between Saint-Joseph-de-la-Rive and the Port of Montréal."
The requested position of forecasts correspond to location of buoys along the St Lawrence Seaway, which are treated as "virtual tide stations." Requests are made every 5 minutes. This requires an internet connection.
When SPINE is enabled, AIS water level values will be ignored for purposes of the Track Nearby Tide Stations and related features.
- Australian Tide Stations (AHS): (Only SEAiq Pilot) Enables download of stations for Austrlia, Antarctic, and South Pacific. The stations are displayed as symbosl with links to online data. When enabled, an attempt will be made to update these every day.
This requires an internet connection.
- Pegel Online Tides (Germany): (Only SEAiq Pilot) Enables download of real-time water level data from PegelOnline (https://www.pegelonline.wsv.de). When enabled, an attempt will be made to update these every 10 minutes.
This requires an internet connection.
- Norway Online Tides: (Only SEAiq Pilot) Enables downloading a list of stations for Norway. You can graphically select a station to get a link to official online tidal data.
This requires that an internet connection.
- Port of London: (Only SEAiq Pilot) Enables download and display of real time water level for a few stations near the Port of London. Currently, there are two stations available, each of which are displayed in 2 locations. An attempt is made to update the stations every 2 minutes.
- Port of Rouen (France): (Only SEAiq Pilot) Enables download and display of real time water level for stations near the Port of Rouen. An attempt is made to update the stations every 2 minutes.
- AyeTides: Enables integration with the AyeTides and AyeTides XL apps. You can graphically select a station to get a link the station.
Pressing the link switches to the AyeTides app and shows you data for that station. When done, you can press the back button in AyeTides to return to SEAiq.
This requires a purchase of AyeTides or AyeTides XL app. An internet connection is initially required to load the of stations. Once stations are downloaded, AyeTides can be used off line.
- Open AyeTides: Tapping on this item will switch to the AyeTides or AyeTides XL (if installed) in order to view tidal information. The current position in the chart display is given to AyeTides so it will show tidal stations in you area. When done, you can press the back button in AyeTides to return to SEAiq.
- Select Stations: A Variable Range Marker is used to identify the area where you want stations data downloaded. Every station contained within the VRM will be attempted to be downloaded.
- Update Stations: Press the Update button to begin downloading station data.
- Status: Status of downloaded stations. You can view the download status for all stations here.
- Erase Downloaded Data: Press the ERASE button to erase all downloaded prediction data.