Thanks for your insights.
I've been sailing back from the 50's and have been on and owned numerous boats with hank on jibs. Still this hook arrangement doesn't make sense to me if it's meant for reefing because there are 2 hooks........and I doubt two reefed sails would be flown at once.
IMO: Not really mean't for reefing a hank-on jib, Although it would do the job just fine.
Some other brands have "curly" hooks and some have straight down hooks.
Remember, to reiterate again, the other needed part of the scheme is the shock cord loop seized just above the hook, that is stretched down over the hook to hold the tack of the jib in place.
Main purpose was for sails hoisted on a "Head Foil Two" double groove jib sail setup. Matter of face our boat came with one. Not wanting to deal with a semi-uncontroled genoa all over the deck (and probably over the side, given our total cruising crew of two) we changed it out for a new Harken RF system in '95, not long after buying our boat.
The prior owner had contracted this boat out to a sailing club. He did not race it, AFAIK, even though he obtained USSA sailing numbers.
Boats rigged like ours and the 80's Ericsons have enough "spare" halyards to raise a different size jib before lowering the one already up.
This sort of assumes that you have a foredeck person to connect the tack and start the jib luff tape into the feeder and then into the slot.... no problem with a racing crew.
Loren
ps: our prior 26' boat was all hank-on, and even came with a 110% jib with a slab reef in it that would be used similar to what Christian described. I actually tried a couple of times in heavy air. Way too much hassle to transfer the sheets or re-lead new sheets on a rolling deck.
Of course that was not really the fault of the boat!