Came out to the boat and found the topping lift had blown off in last Saturday's storm, pulling both screws out. Took the boat out with one of my new crew to get familiar with the boat. Forecast was 10 knots with gusts to 16. Turned out to be 8-12 as we started, rising to 17-18 sustained as we got out of the lee of the headlands blocking the wind's full force. Had main up only. Upon tacking from starboard onto port, right past Mark B, saw that port (windward) upper shroud was no longer on spreader tip, meaning the rig was held up by just the fore/back stays and the inner shroud. Started the engine and took down the main as fast as I could while my colleage steered beautifully. Once it was down and lashed to the boom (and out of the water...), drove home and put her back on the lift. Took off the main and the jib, to reduce stress on the rig, and took the spin halyard and attached it to the port chainplate, to help give the rig some balance.
Prior to going out I had checked the shrouds with the Loos gauge, and they'd shown 30 on the stay in question and 35 on the others, and felt tight. Once underway the port outer shroud was too loose, and I tried to tighten it while underway, but could not, given the wave action in the whitecaps we were experiencing by then. Learned that this was not enough tension on these shrouds!