Are you 100% certain that things are solid glass, & not cored, in that area? What is the span distance between any kind of support structures, or stiffeners? And what kind of glass thickness is present in the various areas nearby, as well as under the head, & in the patch?
Given your statement about how she is built (or built in theory, at least). I'm also wondering if there was orignally a supporting structure underneath of the hull's skin, that the skin was originally attached to. But now either it's no longer there, it's severely degraded, or that the patch isn't resting on it/connected to it (it being a frame, ring frame, stringer, bulkhead, grid/grid flange, etc.).
Any chance you can talk to the folks who did the
repair, & that they have pics &
documentation of the
repair? And be humble, & non-accusatory if you do know who to ask about this. Playing dumb might be smart in this instance, at least until it isn't. In order to have better odds of
learning the truth of things about this. But prior to asking, ensure that you know as much about the
boat, her design & construction, as well as
boat design, & construction in general, as you can. First.
It would be wise to get a hold of the factory drawings (blueprints),
layup sked, & construction sequence for the boat. That area in particular. Since they'll help you to both diagnose what the underlying problem may be, & to
rule out what it (probably) can't be.
Said info will also guide your decision making process in deciding what options to best plan on for fixing things. Such as what you'll be able to tie (connect) your
repairs to.
For other, non-factory, sources of info. Do some searching through the files of
Hunter owner's groups, & on Facebook or similar, etc.
Bottom line, you need to determine what is there now. Especially the bits that you can't see, along with those that you can. And then figure out the right diagnosis (or hypothesis), before you figure out what your options for fixing it are. Otherwise you're doing surgery by braille (at best) on an unknown species. IE; you don't currently know what's in there, so you can't well say what the problem is, & how to sort it out.
Which, I could toss out a dozen fix-it ideas, but they'd all be guesses at present.
Also, I can't think of many (if any) places on a boat with a 4' span that's unsupported in one direction or another. So either your descripton of the area in question, & the problem is off. Or something truly unusual was done when designing & building her.
Edit: Pics of the problem area would help, & be sure to also post ones of all nearby areas & structures. Including ones bonded to the hull that stiffen things, or support furniture, etc. Such as bulkheads, grid, liners, ring frames, stringers...
What year is your boat, & why is "Hunter H23" underneath of your user name (instead of say "Hunter 30")? Can you share what you know about the cause of the damage which necessitated the repair, please. Also, find out what materials were used in the repair (resin & glass type), & in the boat's original construction. And a short synopsis of your level of expertise in both boat construction & repair, as well as tool expertise would help us to better tailor our responses for you.