The deck around the mast step has about a half inch depression from level. I've also noticed the cabin headliner is pressing onto the cabin bulkhead directly below the mount to the point that the door to the forward berths is sprung and closed with difficulty. My question is if I place a bottle jack on a piece of 3/4 plywood to spread the force on the cabin floor and use a 4x4 to press against the headliner below the step and apply pressure, will I be able to reverse the dent, or will I be damaging the truss?
Without seeing it, it's hard to tell but it sounds like your plan is to 'treat the symptom rather than the disease'. Deck sag at the mast step could indicate a serious problem caused by either too much tension in the rigging or, if there is wood under the post, some wood rot.
Obviously, the fix depends on which.
Obviously, the fix depends on which.
When I bought this boat she had been abandoned by the heirs of the original owner who didn't want the boat or the yard bill. She had sat for 11 years at that point with her mast up and rigging so tight it whistled in the breeze ... and her hull was full of water up to the companionway because her cockpit drains were clogged with leaves, you get the idea. There's a teak edged 1/2 inch plywood bulkhead that doesn't show signs of deterioration or rot directly below the step. I've heard there's an arch in the crown of the cabin between the cabin headliner and the deck. I don't know what the arch is made of. It could be made of stainless steel, could be laminated wood. If I push up on the arch and its stainless, I might bend it back into shape. If it's made of laminated hardwood, it might break. If it breaks, I'll build a strut beneath it. I'm looking for experience and/or ideas.