Estimated Position Calculator

Where do you think you are right now? Your dead-reckoned position is where the helm has put you through the water. Your estimated position adds in the tidal stream (and leeway). This calculator plots the classic three-arrow construction so you can see the difference at a glance.

What it does

Enter your last fix as the start, then:

• The course steered and speed through the water.

• Optional leeway: signed, so positive = drift to starboard of heading.

• The set and drift of the tidal stream over the leg.

The chart draws:

1. The Fix ⊕ at the origin.

2. The water track to the DR position (△, oriented along the water track).

3. The tide vector from DR to EP (□).

4. The resulting ground track from Fix to EP: with course over ground and speed over ground.

Use the layer toggles to switch each vector on and off for teaching.

When to use it

• Routine DR updates between fixes on a coastal passage.

• Tidal stream practice: pick a stream from the almanac and see how it shifts your position over the next hour.

• Training plot exercises: work the construction by hand and check against the calculator.

Notes & conventions

• All bearings in degrees true.

• "Set" is the direction the stream flows towards.

• Leeway is added to the course steered to give the actual water track.