Helicopter Rig

Rik - I only use two beads, one either side of the swivel. i used a bead with an oversize(like 3 or 4 mm)hole where you've got the 5mm and put a blob of pva string behind it to stop it slipping just to make sure the knot went thru the bead. i still worry about weed collecting on the knot/in the limpet loop, but its better than 30 or 40 yds of line. thats mainly why i use a nylon leader with braid, not so much the shock absorbtion, more the fact the leader will break before the braid, so at most its 20ft(which is still too much). when testing rigs "fallapartability" you have to pull from all angles, with the line tight and slack before deciding(thats not aimed at you rik!)
shouldn't we also use weaker hooklengths than the mainline to ensure they're not towing line??

Several points mate.

I never, ever knot PVA above a lead or rig.
Tightly knotted PVA very rarely melts, but just hardens, this will have all those tether implications.

Lighter hooklinks are all well and good if need be, but a thethered fish on 15lb mainline and 12lb hooklink is still going to damage itself getting free.
Better for the hooklink to come away.

I dont knot, wet it and wrap it round loosely - just enough to stick.i've never had it come back when i've reeled in, even in winter.

I used to use the cv safety rig, but didnt feel leadcore would "fold" thru the eye, especially if it got kinked. i pulled a line trailer out of a lake last year that had a perfectly "safe" rig attatched, which had worked in so much that the hooklength had gone over the leadcore, but there was a birdsnest 40 yds down the line stopping the hooklength coming off (it was by its head when i pulled it in) the answer? no idea! you can only do so much. stop using hooklengths!
The comment about hooklinks was just a thought as i usually use 15lb+ - ever tried snapping 8" of 15lb line by hand? even 6lb is hard enough. normally when hooklinks break, its because they've been damaged in some way.

Too true about the hooklengths, as you say, you can only do so much.

Barbless cause too much damage and and barbed don't fall out. (not that barbless will fall out when a fish is trailing, too much weight holding it in)