The body was spotted off the docks, actually, which is very close to the mouth of the river Hull, the police searches continued off Paull due to information about currents etc iirc.
Paull was first mentioned as an alternative to St Andrews Quay, as a location accessable directly to the Humber, because some people dont believe the River Hull would be capable of carrying a body that far.
I was originally one of those people who didn't believe that the River Hull was capable of carrying the body that far without it being spotted by someone en route, though I have now shifted my stance a bit and I am trying to keep an open mind on the subject.
I'm putting this up on here for several reasons. One, it will immediately show that I am a duffer at maths and physics, but then I have lived with that since failing O Level maths and dropping physics like a red hot brick in the third year. But I'm also posting it in the spirit of the Zen aphorism that says if you ask a question, you look like a fool for a moment, but if you don't ask, you remain a fool all your life... so bear with me.
It's about the length of time which it was likely to take for an object to float from Oak Road Playing Fields to the confluence of the River Hull with the River Humber. Which is about 5 miles.
Someone suggested in an earlier thread chucking a beach ball with an EPIRB tracker or similar into the water at Oak Road and then measuring how long it took to exit into the Humber. Of course there is no real correlation in weight and size, but perhaps there exist equations that say "if a body of mass m takes five days to do five miles then a body with mass m x 10 will take..." and so on. I have tried googling to see if I can find anything but to be honest, unless you know what you are looking for - what it's actually called - it's a complete mare's nest.
I understand from previous postings that the human body first sinks, then after a while, rises and bobs/floats just about on/under the surface of the water. Libby went missing on 1st February and was found in the Humber on 20 March, IIRC, which is 48 days in the water. As the water would have been very cold at that time of year, one could reasonably assume a period of say, up to 7 days before the body floated and began to be moved by the currents and tides.
One thing which would really help - perhaps police already have this - is the details of the rate of flow for the incoming and outgoing tides up the River Hull and also the underlying current flowing down the river as it drains the surrounding low-lying countryside.
It seems to me that if it was possible to access these figures, it might then also be possible to estimate the time taken to travel the 5 mile distance which in turn could throw some light on the feasibility of this, and other, theories.
If you assumed, for instance, that there was an underlying drainage current of say 0.25 mph always flowing down the River Hull, then this would modify the strength of the tides (I've just plucked that figure out at random, by the way)
The tide doesn't come in all at once at a uniform rate. If you take 12 hours as being a tide, it starts off for about 3 hours at a lower speed, then you get the main bulk of it, then finally, as you approach full tide, it slows down again. So, with a tide of say, 1mph, again a figure I've just invented for illustration purposes, it's possible to construct a crude model that says the first three hours of the incoming tide moves upriver at 0.5mph, the next six hours at 1mph, then the last three before full tide back to 0.5mph again. But pushing against this is the underlying drainage flow, reducing those figures to 0.25mph, 0.75mph and 0.25mph respectively.
Going the other way, the tide going out, down the river, speeds up because of the underlying current, and the first three hours would be 0.75mph, the main bulk of the tide at 1.25mph and the last three hours down to low tide at 0.75mph again.
So. If we could find an equation which tells you how far a body with mass m is propelled along a distance d (which we all know already is 5 miles) then you could work out how many days it would have been likely to take to make that journey.
Earlier on, I thought I had cracked it by trying to work out how far the distance was in a 24 hour period, so I added up the three periods of incoming tides, to give a total of 1.25mph, then the outgoing tides at 2.75mph, took one from the other, and assumed the body would move 1.50 miles down stream in one hour. Clearly this is far too fast, as if that were the case, Libby's body would have cleared the mouth of the Hull within a couple of days at most of rising to the surface, and in any case, I know, these aren't the real figures for the tide race anyway, just ones I made up to test my theory.
And of course that would also assume that a body on the surface of the water would move at the same rate as the water itself, which ignores the effect of drag. Although only a young girl I would have imagined Libby would have weighed around 7 or 8 stone.
At this point, I thought I would put my stupendous ignorance on public display, just on the offchance that one of the posters on this thread knows the real figures, works for the coastguard or the Humber Conservancy Board, or is a marine engineer with a degree in applied maths.