FA-69032 / Tide and marine navigation tables / Member archive

Course to steer across a stream: Speed made good ignores the along-track stream · case 02

Fair and foul streams give the same ETA.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Input [track, boat_speed, set, drift] with degrees true (set is the direction the stream flows toward) and knots. Cross-track stream c=drift*sin(set-track); heading = track+asin(-c/boat); SOG=boat*cos(asin(-c/boat))+drift*cos(set-track). Return None when |c|>boat or SOG<=0, else [heading mod 360 rounded to 0.1, SOG rounded to 0.01].

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
course to steer across a stream [200, 4, 20, 3]	`[200.0, 4.0]`	`[200.0, 1.0]`	Failed

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