Let me start by saying that I am not querying the coordinates (29 degrees 50.36 minutes North 048 degrees 43.08 minutes East) for the Indian merchant vessel given by the UK MOD. In the British version the incident took place at that vessel. They said that the Indian vessel was anchored at these coordinates for two days.

By contrast the Iranian government has given four different coordinates, allegedly referring not to a single incident but to the course of the Royal Naval vessels.

My point has been all along that the precise coordinates are a red herring, because the maritime boundary has never been agreed. There is therefore no clear “line” you can be one side or the other of.

But I have been contacted now by three independent people – two claiming experience as mariners – to make the following point. To the best of my ability I have checked it out, but I am not a qualified navigator. I am not claiming that the following is correct – it is put forward as a problem, not a solution. I am appealing for assistance from those technically equipped to throw any light on this problem.

The MOD claimed that the Indian merchant vessel was anchored “in the channel”. But these coordinates are over a nautical mile further West (ie towards Iraq) than the channel. That bit I am quite certain of.

The mystery is this. On British nautical maps, 29 degrees 50.36 minutes North 048 degrees 43.08 minutes East is 100 yards above the low water line. That is to say it dries out at low tide. The vessel pictured by the MOD is a substantial merchant vessel. No captain of such a vessel would knowingly take his vessel to such a position, let alone anchor it there for two days.

In fact legally those coordinates are on land.

As always, it is a bit more complex than that. British charts use the Lowest Astronomical Tide – that is the furthest the tide normally goes out in a year. So on British charts the vessel is 100 yards above the low water mark when the tide is at its lowest. US charts, which show a more normal low tide, show it as being just below the low water line. But that still puts it in very shallow water indeed.

Consider this. There is very little tide in the Gulf. The highest tidal range there is a vertical fall of only nine feet, and that is closer to the Arabian sea. Perhaps someone can find the draught of the Indian vessel when it left port (Lloyds List should have this). But it was laden with cars. I cannot conceive of it having a draught of less than twelve feet, possibly a good lot more.

In short, unless I am missing something very important, it looks like it would be very hard to get that Indian vessel to those coordinates at high tide, and it would certainly ground at low tide, pretty well at any time of year.

Before we leap to any conclusions, I can see at least three other possible explanations:

The mud and sands have shifted substantially since the charts were made, or it has been radically dredged

Sea levels in the Gulf at the time in question were, for some reason, unusually high; perhaps with some very local effect from very high outflow from the rivers

Neither the people who contacted me nor I can read a chart properly

What I am looking for are technical contributions to explain the alleged problem. Until we have clarified that, I would be grateful if the political pundits could hold fire. I am not saying that the coordinates were wrong, or that the ship could not be in that position.