Working on the engine hatch.

[Buoy]

Finally got back to work on the boat today.
One of the things I'm working on is the engine hatch.
It has a "broken back".
It is radiused to a curve to fit the boat, but one (or more) of the ribs under the hatch have sagged.
When Sean had the boat, he must have had some Heffers on it, or jumped up and down on it himself
Towards the Bow, it is too wide, and rubbing the gunwales when it closes.
Before I paint, I want to fix this and make sure I have clearance/ gap lines.
I'm aiming for a 1/4" each side.
The hatch has 3 ribs under it, and the aft has plenty of clearance, the rib to the Bow needs more "arch".
I pulled the hatch, measured st the bow rib, and realized I need to pull it tighter by almost 1".
I layed it out on saw-horses, and pulled out some pipe clamps to bring it back to the curve it should be.
My plan is to grind down to the glass on the Bow rib, and then re-glass over it to bring it back tighter to the curve.
Should I over-compensate to allow flex??
How much??
How much glass and resin??
I'll add a few post with pics to explain.