Had a wonderful sail last weekend on my '79 H33 with a WSW wind at 10-15. Never tacked or jibed once the whole way from slip to anchorage, and the return trip was more of the same. Maintained a steady 6 knots on a close reach with the 150% genoa for the return trip. I started-up the old Yanmar 2QM15 upon furling-in the ginny and flaking the main and quickly realized there was no forward or reverse (no loud bangs either). I Immediately put out the genoa again and sailed safely back to the slip (though admittedly somewhat awkward arrival). A quick look in the engine compartment made the problem clear. The prop shaft backed-out of the coupling about 3 inches. Presumbably by the mere force of the water under the hull on the 3 hour close reach. I've now read up on this subject and heard the many stories of the coupler separating under power where it bolts together. However, not once have I heard of the shaft getting pulled out of the coupler, especially while under sail alone. I backed out the bolt that is supposed to lock the shaft in place and then dove into the crystal clear waters of baltimore's inner harbor to pound the shaft back into the coupling with the key inserted. I managed to get the shaft about an 1 & 3/4" into the coupler, but it's evident that it should go in further. Before reinserting I verified there were no obstructions on the interior of the coupler. Yet, no amount of pulling, prying, pushing or pounding would get it further in. I tried backing out the packing gland to lessen friction on the shaft, I even clamped a vice grip on the shaft (with fabric to prevent scratching). By 10pm I had enough and inserted the set-bolt again and fired her up. She moves well in forward and reverse with no apparent vibration (no more than usual). However, the shaft is still further back that it should be. Looks as though I'm going to have to interrupt the fun summer sailing with a haul-out and expensive fix. Question: Is there supposed to be one or two bolts tightened against the shaft in the outmost coupler (mine only has one)?Does anyone have any other thoughts to get the shaft back in place?As always, many thanks for the insights.