by Gary Bodie
Here's the short answer, ease the spin sheet, skipper heads up to closer reach, trims mainsheet appropriately, then reaches in and uncleats the spin halyard. Spinnaker streams along to leeward, a few feet above the water, causing remarkably little drag. Leave the pole up, guy cleated, and spinnaker streaming until after you round the leeward mark. Trim in main and jib, sail close hauled, and then hand the extendible tiller and the mainsheet to the crew on the wire. While sailing upwind, skipper goes forward, takes pole down, drags spinnaker around forestay into windward (port) bag, hook halyard, clean up spin sheets, move aft and take back the tiller and mainsheet.
Technique is similar if you're not laying the gybe mark, break chute, head up, release halyard, sail to gybe mark with spinnaker streaming, bear off, re-hoist, gybe, sail 2nd reach.
The key element is that you do not hand the tiller to the crew on the wire while you're on a reach, and you do not try to get the spin in the bag while you're on the reach. The ride is too hairy, and you'll wipe out exchanging the tiller extension, and the sheets if you try it any other way while you're madly planing. Even super crews will have great difficulty managing the tiller and sheet from the wire on reaches. Once you turn upwind, it's still hairy enough, but the motion is regular enough, and the required easing and trimming of the main is much less, so the crew can manage it and stay on the rail. Remember, when the spin breaks on a really windy reach, you need to trim a lot of main, and head up significantly or the crew gets doused. I've tried all of these mistakes in real conditions, and this is the way to go.
The question with a launcher is who pulls the retractor line; skipper or crew ?? I firmly believe that you should avoid transferring the mainsheet and tiller to the crew while you're on a hairy reach for the reasons already described. So that implies that the skipper hands the retractor line out to the crew on the wire, and he/she pulls the sail down into the launcher. The problem with that is that if you have the correct length of halyard/retractor line for all other maneuvers, it's too short for the crew to douse effectively. The crew will have to reach in to about their knees, and then pull 6 inches of retractor about 100 times, which doesn't work very well. If you make your halyard/retractor line longer for just this eventuality, you'll have way too much floating around the bilge on normal days, getting hopelessly tangled in everything else, and you'll get mad one day and cut it.
I worked out a really simple and cheap solution to this dilemma when I had a Lindsay with a launcher, and I've since shared this idea with others, but no one has ever copied it to my knowledge (maybe my genius is only apparent to me :) ). Virtually everyone has their continuous halyard/retractor turn around a single block anchored to the inside of the transom. I put a second block at the transom, and led a short piece of line from a cleat on the centerboard case through this second block, and tied it to the turning block for the halyard/retractor. For normal conditions my halyard/retractor was the correct length ( just long enough to avoid elephant's ass on windy runs and reaches). When we needed to do a trapeze takedown, I reached in and uncleated this short piece of line, which allowed the turning block for the halyard/retractor to slide forward on the floor of the boat about 2.5 feet until a knot fetched up on the other block at the transom. Voila, my halyard/retractor was 5 feet longer, hand it out to the crew, he douses, full plane, blasting over hapless bag boats !! Yes, there are a few other details, depending on whether you're sailing with knots in your sheets, and so whether you can do a full douse with the pole up, but you can work those out, or ask me again. And yes, it worked really well in my Lindsay, because there was no spine in the center of the floor, aft of the trunk.