Use this sailing calculation as a planning or educational cross-check for navigation, wind and current, rig loads, stability, anchoring, tides, visibility, performance, or recovery under explicitly stated conditions.

Near surface current (kt)

Current speed in the near surface layer.

Deeper layer current (kt)

Current speed in the deeper layer.

Compute the signed current shear across the boundary between the near surface layer and the deeper layer as the near surface speed minus the deeper layer speed. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Shear gain (kt)

Signed shear in knots; positive when the surface runs faster than the depth.

• Actual conditions change with vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, regulations, and safety margins. Simplified formulas do not replace seamanship, approved stability data, or current navigation information.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check official charts, tide and weather services, instrument data, vessel manuals, and collision regulations; maintain conservative margins and a safe alternative plan.

• Current Correction Angle Calculator

  Compute the signed crab angle needed to oppose a current's cross-track component. Routes whose cross-current exceeds boat speed cannot be held.

• Ferry Glide Course

  Calculate the heading to steer so cross current lets the boat ferry glide onto the desired course, correcting by the arcsine of the current to boat speed ratio signed by the side the current comes from.

• Shift Rate Calculator

  Compute the signed rate of the shortest compass-direction change between two mean wind headings, correctly handling the wrap across north.