Just following a few links on PBO forum and the subject of screw hatches came up. Actually the thread is about a RIB, but screw inspection panels are used on lots of boats. I had them in my last poly fishing rig in the buoyancy chambers …and they did leak from memory, mainly from rain water in the boat when it was not left at a good drainage angle. I’ve come across this info in the ocean rower articles I’ve read also. To actually get true water tight hatches you need a three piece setup similar to this.
These appear to be a similar setup to the cleaning hatch on the top of my pool pump, which obviously has to be watertight as it’s under pressure.
Pic above shows an ocean rower as it undergoes self righting tests. It has multiple hatches of the type shown for many individual water tight compartments. These ain’t cheap
but I guess if your derrière is at stake in the middle of the Atlantic, costs don’t enter into it. I was thinking of adding a hatch to my lower inside transom to replace the lower pintle but needs to be properly watertight. Anyway I’m just more aware now reading all this that if adding a watertight hatch anywhere in your Investigator the ones I’ve used in the past may only be “water resistant “
Anyway, F everyone’s I.