Let us take a look at removing, restoring and replacing the plate, which at 175 lb of cast iron and not something to fool around with.
First remove thwart and capping. Lower the centre roller on the trailer to let the centreplate drop and allow the pivot bolt slot in the plate to become vertical. Pass a loop of old webbing strap down the aft end of centreplate case, assisted by a long thin piece of wood. When it emerges at the bottom ease it forward to become a strop around the lower end of the plate.
With the aid of one or two friends put two stout planks either side of centreplate case, on top of the floorboards. One person at the front takes hold of the centreplate horn, the other person at the aft end takes hold of the webbing strop. Lift together, with front end 6 to 9 inches higher to clear bolt slot, once clear, level the plate, lift out of the case and rest on a plank. Place an old blanket on the side deck to protect it, lift the plate and lay flat on the blanket. One person steadies the plate while the other gets out of the boat then he steadies the plate from outside the boat while the first person joins him. It is then a straight lift down to the ground.
Fettle the plate to as fair a surface as is practical. It is not worth trying for a knife-edge on leading and trailing edges, just get the shape smooth and fair. Weigh the plate (170 to 180 lbs). Have the plate sandblasted. The finish can be galvaised, painted with Hammerite, conventional or two- pot paint, however I believe pigmented epoxy coatings will give the best finish and life.
Replacement is a reversal of the above procedure taking care not to damage the new finish, or give yourself a hernia!