While at Need entry for HomeDepot , also got a Ridgid quarter sheet sander and several sheets of 150 grit sand paper. Used this to remove the bottom paint from the outside of all thruhulls: cockpit drains (2), engine intake, galley intake, galley exit, head intake and head exit.
Using a 12" adjustable wrench to fix the nut on the galley seawater intake thruhull and another adjustable wrench to turn the galley seawater intake ball valve, attempted to remove the ball valve from the thruhull. Instead the plywood of the backing block gave way with two layers of the plywood separating cleaning due to the torque. The "thruhull", half the backing block, the ball valve, and the tail piece all came out as a single unit. Clearly the ball valve is more strongly attached to the "thruhull" than the "thruhull" to the hull. The 12" adjustable must have slipped from its position allowing the fixing nut to rotate some amount and the bonding between the different layers of plywood to shear.
Not good. Confirms that these 1/2" thruhulls must be replaced.
Galley seawater intake
Oblique view of galley seawater intake after removing "thruhull"
Galley intake valve and "thruhull"
Galley intake valve, "thruhull", and half the backing block
Sheared plywood backing block for galley intake
Galley intake ring waterside
Galley intake ring hullside
Galley intake ring thickness