Helmwright Nautical Calculator

What it does

Helmwright is a navigation calculator for sailors, skippers, delivery crews and navigation students. It works like a hardware calculator: a sea-green chassis, real keys and a clear LCD, with each answer labelled so you know what you are reading.

Worked examples

• Course to steer. 090 at 10 kt against current 180 at 2 kt -> course to steer.
• Speed. 10 NM in 1:15 -> 8 kt.
• Eta. 20 NM at 6 kt leaving 14:30 -> ETA 17:50.
• Light range. 100 ft light seen from 9 ft -> geographic range.
• Tide. 6 ft range, 2 h after low water -> 1.5 ft risen.
• Compass. T 090, variation 10 W -> compass.

How it's calculated

Every trade key and the formula behind it, as shown in the app's key guide. A second legend is the shifted function.

Dist ETADistance / Estimated time of arrival

Stores the typed distance in nautical miles, or solves D = S × T from speed and time. Shifted takes a typed departure time (14 Hr 30) and gives ETA = departure + D ÷ S; press again for time en route and departure.

Spd HullSpeed through the water / Hull speed

Stores the typed speed in knots, or solves S = D ÷ T. Shifted takes a typed waterline length (feet, or metres in metric) and gives hull speed 1.34 × √LWL knots; press again for the speed-length ratio.

Hr TimeHours / Time

Hr enters hours; digits after it are minutes, so 1 Hr 15 is 1:15. Shifted stores the typed elapsed time (a plain number is hours), or solves T = D ÷ S as hours, minutes and seconds.

Fuel RateFuel on board / Fuel burn rate

Stores the typed fuel on board (US gallons, or litres in metric); press again for endurance = fuel ÷ rate, range = endurance × speed, fuel for the trip and the reserve left. Shifted stores the burn rate per hour.

Crs CMGCourse steered / Course made good

Stores the typed course steered (degrees true). With the course to make good, speed, set and drift stored, gives the course to steer against the current; press again for speed made good and the correction. Shifted stores the course made good, or works it out from course, speed, set and drift.

Set DriftSet of the current / Drift of the current

Stores the typed set (direction the current flows toward). With course, speed and time run, and the fix as CMG and distance from the start, gives set and drift from the DR position to the fix. Shifted stores the drift in knots.

T>C C>TTrue to compass / Compass to true

Converts a typed true heading to compass: M = T − V, C = M − D, east positive; press again for true and magnetic. Shifted goes the other way, M = C + D, T = M + V.

Var DevMagnetic variation / Compass deviation

Stores the typed magnetic variation, east positive, west negative (10 W is 10 then the sign key); shifted stores the deviation for the heading the same way. Both are 0 until set.

Eye LightHeight of eye / Light or object height

Stores the typed height of eye (feet, or metres in metric) and gives the horizon 1.17 × √h nautical miles; press again for dip, radar horizon 1.22 × √h and the height. Shifted takes the light's height and gives its geographic range; a typed angle gives the distance off by vertical sextant angle.

Tide RangeTide by the rule of twelfths / Tide range

Takes the time since low or high water and gives how far the tide has risen or fallen by the rule of twelfths (1, 2, 3, 3, 2, 1); press again for the change still to come. Shifted stores the range, or a typed time as the tide duration (6 hours by default).

For passage planning and training. Not a substitute for official charts, tide tables, notices to mariners or proper watchkeeping. Verify every result. The developer accepts no liability for loss or damage arising from use.