Free tool · Binnacle Passage

Squat & Under-Keel Clearance Calculator

Estimate squat by the Barrass rule, build the UKC stack, and back out a maximum safe speed. Everything updates as you type. Nothing is stored or sent.

Vessel classSets a starting block coefficient (Cb) — adjust below

Block coefficient (Cb)

Speed (knots)

Channel

Charted depth (m)

Height of tide (m)

Static draft (m)

Required UKC (m)

Other allowance (m)heel, wave, datum

WITHIN MARGIN

Margin vs. required UKC: 0.02 m

Available depth (charted + tide)15.50 m

Static UKC (available − draft)3.00 m

Squat at this speed− 1.68 m

Dynamic UKC (after squat + allowances)1.02 m

Maximum safe speed10.1 kn

Estimate only (Barrass rule of thumb). Real squat also depends on blockage, trim, and channel form. Always apply the ship's UKC policy and the pilot's judgment.

Binnacle Passage carries this calculation on every transit — agreed speed and clearance, recorded with the rest of the passage.

Binnacle Passage for pilots →Read the field guide