Wet Willy said...easty said...Doesn't downhauling the sail pull the masts back together? Obviously not, or this topic wouldn't exist.

Some masts are so precisely engineered that the join is airtight, and when you slide the halves together, there's air pressure inside which pushes them apart a few cm. But if you hold them tight for a few seconds the air will find a way out, and the halves will stay together.
Just thinking about this (red wine and the rest of the week off makes you do that), but if this was so, wouldn't the airtight join, together with a small leak for the air to get out, together with the constant flexing of the mast while sailing creating a pump effect within the mast, contribute to masts sticking together? Which by the way I've never had happen. Must be the cheap masts again.
Also both my masts have holes in the top of the top section, plus the 400 is open at the top of the bottem section, surely most masts are like this, which would immediately let any compressed air out?
Disclaimer - I'm no engineer, had a red or two, and it's going to be windy tomorrow