: I'm still trying to decide whether to start from scratch or to rebuild this
: puppy. The deck and coaming are easily reparable. My current thinking is
: to replace up to 24" of every hull panel, one at a time to maintain
: the stresses and shapes in the hull as much as possible during repair.
: This will take lots of time, but hopefully less than building a new boat.
: Any thoughts from anyone with experience repairing S & G boats?

Sure you can't just wrap some duct tape around that and paddle it?

No real experience in fixing one with this kind of damage, but if it were my boat I'd fix it. Far cheaper, far faster than building again from scratch.
First get a sheet of the same size and color of wood as the original. Match the size exactly (4mm, 3mm, 1/4 inch, whatever) and come as close as you can find with the color. Next get a 1/4 sheet of inexpensive 1/4 inch plywood (They sell these by me as precut 2x4 foot "handi-panels")and a 3 foot 1x10 or some 3/4 inch plywood of about the same size.

Start on any hull panel and probe outward to your left, from the damaged area until you find where the wood is solid and undamaged. Go two more inches to the left beyond this point and draw a straight line from one edge of the panel to the other. Eventually you'll cut out the panel here, and splice in the replacement, so you want to make sure you are connecting to good wood. I like your idea of replaceing 24 inch sections. Measure 23 3/4 inches to the right from this line and draw another line. (When you cut on these lines you'll have a hole a bit smaller than 24 inches, and you can do the final fitting easily.)

Now move to one of the adjacent panels. On this one you want to start by going to the right of the damage to find solid wood, and then go another 2 inches to the right for your line. from this line you measure to the left ( going over the damaged area, for your second line.

Repeat this process going around the hull, until you have marked each hull panel. Go to the left of the damage on one panel, and the right on the next and the left on the next and the right . . . You will end up with a very staggered arrangement penciled onto the hull.

Stabilize the hull in the proper shape before you do any cutting. Use the 1x10 or a piece of 3/4 inch plywood as a partial bulkhead or template of what the interior should be. Draw some alignment marks on the inside with a pencil. Trace the interior onto a piece of cardboard and transfer this to the board. Cut or sand it until it fits snugly while holding the sides in the proper position. You can nail some scraps on this to provide references for the floor and deck. Try to do this as close to the damaged area as you can. If you want to make 2 templates, do one fore and the other aft of the damage. One should do you, though.

Get some newspaper pages, or large sheets of drawing paper and lay one on the hull over the damaged are. Tape it in place over one of the 2 foot sections you penciled earlier. Use a crayon or bare pencil lead and trace the edges of the hull panel. Transfer to this paper the location of those lines you drew on the hull. When you are done, these pages will be your patterns for cutting new hull panels. Label them (A,B,C, etc.) and label the hull area that matches them)

Cut eight 22 inch long by 4 inch wide strips from the 1/4 inch plywood. Coat them on one side with some epoxy, or another strong glue, if you like, and screw them to the hull as reinforcements. They will bridge the damage and secure things. You want these pieces to fit inside the areas you have pencilled in. As you cut out the damaged areas the entire reinforcement piece should come with it, so cut these things smaller if you need to. Instead of screws you might be able to use 1/2 or 9/16 inch staples and bend over whatever protrudes. Use the template/bulkhead to check that the alignment does not change as you secure these reinforcements.

When you have the damaged area stabilized at the proper shape with excessive and redundant reinforcing, and you have patterns for making new parts, then you can start to cut out the damaged area. A short straightedge and a sharp utility knife will do the job of cutting. You'll be going through fiberglass and thing wood. the wood should cut easily, but the fiberglass is hard on sharp tools. Change blades when one goes dull. Use many light cuts rather than trying to force through the material.

You thought of doing one part at a time to maintain stresses and shapes. I'm thinking of doing two adjacent parts at a time, using the added bracing and the template/bulkhead to maintain those stresses and shapes.

Here is my thinking: when you remove two adjacent panels you don't have to remove the fillet that joins them. When you replace these, you wire in the replacements and they should be drawn into shape by the remaining hull, and that template/bulkhead. You'll glue in two pieces cut from your patterns and hand fitted, then you create a new fillet to join these two parts. When you finish with these two parts you do two adjacent panels from the other side of the boat. You can glue in these two pairs of parts on one day, but then let the thing rest a week or so while the resin polymerizes and gets good and strong.

Two more pairs of replacements and you'll have replaced 8 hull panels in 4 steps. when you replace these pairs of panels, though, you will be making 3 fillets, not just one, as the last two pairs of panels will attach to the first and second pairs. That's why you want them fairly well cured and strong.

A little sanding before you reglass the outside and inside and away you go.

hope ths helps

PGJ