Originally Posted by Ranger46
Folks, how common was aft deck sag on the 1976 GS 43 MK2. as you can see in the picture, the aft deck is concave by about 1-2 inches in the center on the stb side of the hatch. I have sounded out and moisture metered the deck finding the area under the flybridge down ladder to be soft. other than that it is solid. I went below and checked for deck flex and it seems to be very ridged. I intend to drop the headliner in the aft stateroom to inspect thoroughly as well as tackle the soft spot. Prior to doing that I am looking for any known issues on this model / brand and if this was a known problem? and what others have done to rectify it.
While I don't have any experience with Gulfstars, a sagging soft deck on a 47 year old boat is a very common finding. The core of the composite deck structure (either balsa or plywood) has gotten wet, weakening the ability of the deck to behave as a beam. The fix is straightforward but does require a lot of effort. The wet core probably extends further than the area of local sagging. It is expensive to hire out, time consuming to take on yourself but it isn't terribly difficult and there is plenty of guidance out there on how to do it.
I have never heard of a boat sinking due to a saggy deck but it should be addressed because the problem will only get worse, the hatch will start to leak, if if hasn't already and it will drive you nuts everytime you walk by it. For very small areas, some boat owners have been able to mitigate the problem by drying out and injecting epoxy to replace the core, I do not think this would be sufficient with that amount of sagging. At a minimum, the core needs to be bonded to the upper and lower skin of fiberglass and for large areas, it won't bond unless you get in there and physically remove the rotten organic material and sand the fiberglass to a clean surface able to be bonded to by resin.