FA-68949 / Tide and marine navigation tables / Member archive

Under-keel clearance with squat: Drying heights are added as depth · case 04

Vessels are cleared over banks that dry at low water.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [charted, tide, draft, speed_kn, cb, confined, margin]. Charted value is depth below chart datum (negative means a drying height above datum). Squat = cb*speed^2/100 metres in open water and twice that when confined. UKC = charted+tide-draft-squat. Required clearance is margin*draft. Return [round(ukc,3), ukc>=required].

Why this case matters

Tide tables and passage plans turn published predictions into go/no-go decisions about depth, clearance and timing.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
under-keel clearance with squat [-1.2, 3.8, 1.6, 4, 0.45, false, 0.2]	`[3.328, true]`	`[0.928, true]`	Failed

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