While the 23-2 has nice longitudinal stringer system, oil canning occurs in the aft quarter, noticable when on a beam reach in a moderate chop. In fact trailer roller pads indent the hull even with little hull weight at that point.
The first order of business was to re-build the U shape bilge stringer that bridges the liner/stringer assemblies forward and aft. Stock construction was 10 oz cloth hastily thrown around soft urethane. This was not very rigid and further de-composed when my boats bilge was flooded for a time before acquired from a friends backyard. It was easily torn out. I formed new U shape stringers with stiffer surfboard foam, glassed in with a laminate of mat and then 18 oz bi-axial(0,90 degrees)/ mat. This is visible in the lower right of first photo. Photo is taken looking aft. At extreme right is foam wall of ice box.
The second addition was the lateral rib also shown in this photo. For this I used fir 2 bys with a urethane foam shaped top for proper radius on the glassing. Using wood allows less glassing, as the core is also providing stiffness, provided it is well resined and glassed to the hull, and if not generally in constant water immersion should not be a problem as long as I am alive. It was not an easy area to glass. The same bi-axial glass was used with double layers on the lower 3/4. The upper quarter butts with a tapered wood piece to the berth beam which is tied into the longitudinal liner/hull connection.
The second photo shows a new rib/wall glassed in to the junction of the new fore/aft stringer and the aft end of the cabin sole floor pan. Since there was no hull flex detected in this area 5/8 plywood glassed on each side seems sufficient. The other reason for this addition is to keep stored tools and the like from sliding aft in heavy weather. It also butts up to a berth support beam, see third photo.
The hardest part of the project was the sanding, as ODay did not use a polyester resin white finish interior, but rather alkyd paint. Therefore, it all had to come off where any fiberglassing is to adhere. Messy, dusty work. I highly recommend an in-line venting fan with flexible hose to suck and exhaust dust out of the boat. I use Vinylester air-inhibited laminating resin, with a final tack free coat applied after light touch up sanding. The bi-axial cloth is great as laminate thickness is built up quickly with huge strength. Be sure that the boat is relieved of any cradle/stand or trailer pad pressure at these points before glassing in any new re-inforcement.
I sailed the boat in heavy wind and chop and all oil canning/flexing - hull shake is gone. And there is no indent from trailer supports either. I am very happy with the job.