Under the hood
Engine demo
This page exposes the raw calculation engine that powers the chart workspace — each card runs one RYA method in isolation, with nothing hidden. Use it to check the maths against textbook worked examples or your own paper chartwork: enter the same numbers you’d use on paper, recalculate, and compare the workings. The planning chart calls exactly these functions.
Streams
Course to steer — vector triangle
The classic one-hour plot: the tide pushes the boat off the ground track, and the boat vector closes the triangle. Outputs the course to steer, speed over ground and ETA — multi-hour legs aggregate one stream vector per hour.
- CTS
- 5°T
- SOG
- 5.3 kn
- Leg time
- 2.01 h
- Track
- 21°T
- Distance
- 10.7 nm
- ETA
- 10 Jun, 11:00
Workings: 3 hourly stream vectors aggregated (net drift 4.5 nm); boat vector closes the triangle onto the ground track. Triangle coordinates ready for the phase 3 chart overlay.
Tides
Height of tide + depth clearance
RYA tidal curve method: take the bracketing HW and LW, classify the day springs or neaps from the range, read the curve factor at your time, and add the result to charted depth to check clearance under the keel.
- Height of tide
- 2.95 m
- Range
- 4.1 m
- Springs/neaps
- springs
- HW − query
- +3.0 h
- Curve factor
- 0.50
- Depth available
- 4.15 m
- Under keel
- 1.85 m
- Clearance
- PASSES ✓
Workings: range 4.1 m → spring fraction 0.95; curve factor 0.50 at HW+3.0; height = LW 0.9 m + factor × range. Phase 3 plots this on the tidal curve.
Compass
Compass — true to compass ladder
True to magnetic to compass: variation (west negative) then deviation interpolated from the boat's card at the compass heading. 'Error west, compass best' — the ladder below shows each rung.
- True
- 179°T
- Variation
- 4.0°W
- Magnetic
- 183°M
- Deviation
- 3.0°E
- Compass
- 180°C
Ladder: T 179° − var (-4.0°) = M 183° − dev (3.0°) = C 180°. Deviation interpolated from the sample card (boat cards arrive in phase 3); variation negative = west.