Originally Posted by Omatako
I have done a lot of sailing on different boats including several blue water passages and I have made a point of doing my turn buckles with lock nuts and I have yet to have one come loose when I didn't want it to or not come loose when I wanted it to.
YMMV, as always. However, the locknuts are counter to basic engineering since any strain on the rigging will be in the direction that will loosen them. I'm sure they work most of the time.
For maximum reliability, they probably should be applied with a torque wrench. You need to produce some deformation and stretch in the turnbuckle threads. This gets added to rigging strain. You want about 75% of this preload to come out at maximum rig load. It all just makes my head spin and I could never be comfortable looking at them on my boat.