For those with the West Mersea combi trolley and that's most of us, make sure to check the drain holes in all the tubular sections as if they're blocked with debris from the beach the trolley can rot away from the inside.
Mine is probably 20 years old and started to suffer break down of the galvanising. While cleaning off the rusty surface I noticed that the drain holes were blocked  with sand, gravel and various debris enough to hold water in the tubes. My 'A' frames were full to about the two thirds of their length.
To solve this problem and clear out the debris I've cut slots in the underside of the tubes to allow the water etc to drain after launching.
Check your trolleys, before they rot away!