Exactly MM43. My post was obviously not well written or too succinct.
Distance from the slick to where the merchant ship first sighted debris divided by the difference in time = velocity = approx 1 knot = the velocity the report stated on page 5 "
After June 7 all the floating remains were entrained to the North by an approximate 1 knot (or 0.5 m s-1) current."
The report basically shows the backtrack could not be done due to insufficiently accurate data for this area so my point was why reject this slick when it fits in with their accurate data although it is in conflict with their extrapolated (ie possibly incorrect and at least inconsistent) model results. IMO they assumed a sudden release of fuel which gave a different expectation so rejected this on an (incorrect?) assumption then also because it didn't fit in with their (inconsistent) modelling. I am not criticising their modelling effort as it was mammoth and they found this satellite image, simply saying they found the modelling was unable to yield reliable results so, on that basis, the slick should have been given more weight.
respectfully, Ian