Tack Pad Documentation

This documentation can also be found in the Tack Pad app itself. Select the “settings” icon on the lower right, then the “Help” button in the miscellaneous section of the pop-up.

Getting Started

Drag the waypoints to achieve the bearing (B) and distance (D) for which you want to solve. Travel always starts at waypoint #1. Pinch to zoom in or out, or drag the background to reposition the waypoints. Select and drag the wind barb on a waypoint to adjust the wind. Drag the barb around the point to set the direction and drag towards or away from the point to set the strength. Wind settings stay in effect until the next point that contains wind information. Read the course (C) arrow which indicates the course to steer as well as the speed (S) and time (T) on tack.

Tack points

Tack points are the intermediate grey points between waypoints. Tack points are normally generated automatically by the solver, but can also be added manually. Tack points can be modified. Dragging or double tapping a tack point puts it into edit mode, at which point it’s considered “user modified”. Modified tack points are treated like waypoints and are not automatically deleted when solving. You can also create new tack points by double tapping on a track between two points (this only works on tracks, not bearings between waypoints.) New tack points inherit the same wind and current attributes as the previous point in the chain. To remove an unwanted modified tack point simply double tap it.

More Waypoints

Double tap on the background to create new waypoints. Double tap an existing waypoint to delete it. Deleting a waypoint also removes all tack points between the previous and next waypoints (modified or not). New waypoints inherit the same wind and current attributes as the previous waypoint in the chain.

Current

The green circle around a waypoint or modified tack point indicates that there is no current associated with the point. Selecting near the point, but not on a wind barb, will allow you to modify the current. Drag the current around the point to select it’s set, and drag towards or away from the point to select it’s drift.

Bearing & Tracks

Bearings (B) are used between waypoints and are only used to describe the relationship between them. Tracks (TR) are the expected course over ground between two points. If a bearing and track coincide, only the track information is displayed. Both are lines drawn between two points.

Course to Steer

The course (C) arrow represents the course to steer along with the speed through the water and the travel time to the next the next tack or waypoint.

Buttons

Buttons on the right side of the display for settings, point information, reversing the direction of travel and swapping between the two pages. Each page has it’s own set of waypoints. Both pages share the same boat settings.

More information

Single tapping a tack point or waypoint will pop up a list of information about the selected point. Use the next and prev. buttons at the top to cycle through the tack and waypoints. This is divided into several sections:

Notes

A general description of the activity at this point

Use Polar

Select whether boat speed and leeway are obtained from the polar table or manually selected

Course to steer

Provides information about course, speed, time and distance to the next waypoint. Speed here is speed through the water.

The VMG value is velocity made good on the bearing between the previous and next waypoints. This will correctly show progress towards the waypoint along each tack. This differs from the VMG reported by a standard plotter, which returns the velocity made good from the current position directly towards the next waypoint. This standard approach to VMG works when motoring but is inaccurate and misleading when under sail.

Track

Information on the track between two points. The speed value here the course over ground speed.

Wind

Wind that affects travel towards the next point.

Current

Current that affects travel towards the next point.

Leeway

Displays the leeway currently affecting the boat. When using a polar table leeway is automatically determined.

XTR

Cross track error is displayed on tack points only and shows the distance from the tack point to the bearing line between the previous and next waypoints. This value has no relation to the track.

Manual Mode

When the polar results are not quite working, or you simply want to motor, then you can use manual mode. When a point is in manual mode you can selected boat speed and leeway, and the polar information is not used. Nodes in manual mode look different, there is no wind barb and a new leeway arrow is displayed instead. Select and drag the leeway barb around the point to select the leeway. In manual mode the course arrow becomes selectable, select it and drag it towards or away from the point to set the desired speed through the water.

Settings

Tapping the settings button will activate the settings popup.

Basic Attributes

Select the VPP and polar which describe the boat’s handling characteristics. Polar and leeway values can be scaled to more closely match your boat’s characteristics. The tack penalty is added to the travel time whenever there is a tack.

VPP & Polars

Polar plots (or diagrams) are a prediction of boat speed based on wind speed and direction. Polars are usually created using velocity prediction programs (VPP) which use a description of a boat’s hull shape and sail combination to predict it’s speed. Manufacturers sometimes provide polars, some are generated buy rule rating systems, and of course boat owners can produce their own. Three VPP files are provided which are average values for three classes of boats, heavy, medium and light displacement. VPP files can contain more than one polar, selectable in the settings. Individual polar files can also be loaded. See the www.ruddernut.com website for more details on the supported formats and how to load them.

Leeway

VPP files also contain leeway information, though plain polar files do not. When loading a plain polar file the leeway is estimated using a simple formula. If you cannot adjust the leeway to match your measured leeway, you can always enter manual mode to get a more accurate result.

Accuracy

This program is an aid to navigation only and can only provide a rough estimate of courses to steer, travel time, etc. There are too many unaccountable variables including wind and sea state, boat idiosyncrasies, sail trim, helmsman and autopilot, to produce an exact solution. The polars and leeway computations are also only approximations of ideal boat performance.

Rhumblines

The solver uses rhumblines for all internal calculations and all displayed information. The same approach you would use on a chart.

Safety

The tacking solution does not take into account any navigational hazards through which you may be sailing. Please consult your chart before you sail. Using Tack Pad in one hand and a chart in the other, so to speak, is the recommended approach.

Finger Action Overview

Double tap

  • the background creates a waypoint
  • a track to create a new modified tack point
  • a waypoint to delete it
  • a unmodified tack point to put it into modified mode
  • a modified point to delete it

Single tap

  • a point to activate the point information popup

Drag

  • the background pans the display
  • a wind barb to set wind direction and speed
  • near a point with no current to add current
  • a current arrow to select drift and set
  • a course arrow (if the point is in manual mode) to set speed through the water
  • a leeway arrow (if the point is in manual mode) to select leeway

Pinch

  • the background to zoom in, out, or pan the display