My Nauticat 33 has some kind of a jack screw that has been fitted underneath the corner post to the head, which appears to support the cabin house and therefore the mast step.
It is sitting on some metal plates resting on top the keel. The top of the jack screw extends through a hole in the sole and supports the corner post directly. This whole rig does NOT appear to be original equipment but was installed later. I have no idea how it was done and I cant see any way to get it out.
It does not seem to be a normal jack screw that gets taller and shorter when turned. Instead it appears to be a long threaded nut with two threaded rods. I can turn the nut but the rig does not appear to get tighter or looser. I can only just see and get a wrench on the bottom of the nut because the jack screw was somehow installed between two transverse web frames that go across the boat, supporting the sole where the forward piece and the salon piece join in the way of the forward doorway. My insurance company wanted it replaced because the petal plates it sits on are rusting. I cleaned up the rust and painted it and convinced the insurance company that it does not need to be replaced, but I am curious if anyone else has seen such a thing under their mast?
Our 1980 Nauticat 33 shows signs of a previous owner’s efforts to shore up this same area using wedges and thick fiberglass structural material. Symptoms of a structural problem include: The sliding door between salon and foreword is very difficult to move and the cabin top where the main mast steps is located is depressed.
I understand that during this period of Nauticat construction, design changes, without proper structural changes, may have caused this compression problem.
Your description suggests that the “jack screw” was an attempt to fix this. Why it does not adjust is a puzzle.
Good luck! Look forward to hearing more.