Through trial and error working on many boats over the years, here is what I found works best for this repair:
1) No material needs to be removed - any removed material decreases the likelihood that you will get an effective bond. It looks like you already have the boat inside. Keep it inside and, if you can, run a blower or through an inspection port to get the inside of the boat as dry as possible
2) Per the comment above re the length of the split, a Laser, or any boat, retains its inherent structural integrity as long as the tube, which is roughly what a hull is, is not compromised. In the case of a Laser, because of some of the particular structural factors, you can, in my experience, work with as much of the split at a time as is split. The Laser hull, because of the integral nature of the deck-to-hull bonding at five key points, in addition to the gunnel bonding- i) bow ii) mast step iii) daggerboard trunk iv) aft end of the cockpit/drain plug and v) stern - will not lose its structural integrity, if the hull is properly supported while you are working on it. Proper supports are sawhorses placed at the aft end of the cockpit and near the mast step. To be cautious, you can put another saw horse at the forward end of the daggerboard slot, which likely take some shimming to get it to carry load. Make sure there are no single-point loads where the deck rests on the sawhorses - use a split pool noodle to distribute the load evenly along the saw horse and make sure there is no wobble once the boat is on the sawhorses.
3) Use a shop vac to get any foreign matter out of the split, but don't be too aggressive, as you don't want to remove hull material.
4) With tape, mount a vacuum, with a partial covering of the stern drainhole, so that you can draw a low vacuum on the hull. You can deform the hull with too much vacuum, particularly if it too warm or too cold, so just enough to draw air in on the splits. Test, but do not leave the vacuum on for the next step.
5) On a day when you know you will not have temperatures either too cold or too hot, i.e. 70F, begin by using an artists thin paintbrush or a pipe cleaner, to wet both of the interior surfaces of the split, hull and deck, with enough water to clearly moisten both surfaces. They should be wet, but not soaked. This dampening is critical to the successful bonding of the glue to be used in the next step.
6) Apply a bead of Gorilla Glue, the original brown stuff, to the entire length of the split, with enough to fill the split. Turn on the vacuum for a quick blast of suction to pull the Gorilla Glue into the split. Reapply another bead of glue to replace what was pulled into the split. Make sure the bead does not overflow the top of the split, but is close. Carefully insert a putty knife on either end of the split to get to good bonding, if there is any, and apply glue in the gap opened up by inserting the putty knife. If you apply too much glue, use a quick burst of suction to get it in the split and reapply glue, as needed. Wipe off any excess glue with a wet rag before moving to the next step
7) Using your previously assembled clamps, wooden one inch battens/paint stirrers/yardsticks and wax paper, cover the split area with wax paper, then a wooden batten on each side of the split, then a clamp every 6 inches. Tighten the clamps from forward to aft and then go back and tighten them more.
8) Let the boat sit for 24 hours.
9) Remove the clamps, battens and wax paper. Shave off any excess Gorilla glue with a straight edge razor or knife, being careful to not scratch the gelcoat.
10) Reverse your vacuum and blow a slight amount of positive air pressure into the hull. Apply soapy water to the split and see if you have any leaks remaining. If there are any, repeat steps 5-8 until there are no more leaks.
11) Go sailing and have fun. In my experience, you will not have to touch a Laser repaired this way ever again - Gorilla Glue is a waterproof, flexible, solid bonding agent that, absent too much UV light, will do the job.
