The deed is done!
Regulars will recall tales of woe with manufacturing/material faults with my tubes after a meagre 300 hours of use in the boat's life, and various failed attempts to solve the problem - I won't repeat the saga here, it is all elsewhere on RIBnet for anybody who wants to read it again but here is a quick pic of the crap gluing on the back end of the tubes to remind everybody:
But after a lot of work and a not inconsiderable wodge of money it now looks like a boat and should be airtight again - a bit of fine tuning may be needed to improve the appearance but in functional terms it should be as good as when I got it.
Firstly I got a pair of these from Paul Tilley:
which when attached to my garage compressor for a couple of minutes look like this:
Removed the end from the tube, cut 2 holes (measure, measure and measure again!) where the inflation valve used to be, and another one 30cm forward of this - I had Paul fit a set of pressure relief valves to the sausages, the original boat never had them fitted and it has always worried me on hot days in direct sunlight.
Deflate the sausage fully, stuff it up inside the tube and get it positioned in the right place. This took half a dozen attempts to get right as it tended to twist around during inflation and I had to let it down and reposition it. I also deflated the chamber in front to remove any tendency for it to push the sausage out, and then blew it up again afterwards.
Lots more air ... and bingo one inflated and airtight boat
I hadn't factored in the slight tapering of the sausages towards the seam so the last inch or so of the tube isn't completely tight but the rest of it is a good snug fit and hopefully won't move as long as there is pressure in it. May trim this back a bit to tidy it up in due course after I have been for a test run or two but I can't do too much without moving the mooring cleat which is a bit of a pain.
And on the inside of the boat it looks like this: inflation valve is in the original place.
Haven't attacked the other side yet as the original tube still holds air on that side but I have another sausage for that side if (or probably when) required.
As long as it doesn't rain I'm off for the first test this afternoon but it's looking good so far
Thanks to everybody on here for sympathy, advice, suggestions and putting up with a thousand questions. Thanks also to Paul Tilley for making the solution for me, I would recommend Paul's work to anybody who needs tube work of any sort, I just sent off the measurements and the perfect solution arrived