Prereg p4 (4 Nov 00:55, before running): single changepoint per ship from partner-adjusted daily estimates.
Expect: of the 14 |z|>3 ships, >=10 show a significant single step (perm p<0.01); steps cluster at long gaps (>60 days between obs, e.g. ship returning from refit). Of 10 random non-drifting ships, <=2 significant.
