best hammer for hull test ?

I've seen most surveyors use a small ballpeen hammer, using the flat side to strike the hull. Hold the hammer at the end of the handle and tap the hull. The idea is not to strike the hull hard, but with a repeated movement to listen for the sound of the tap.

Taps the "ring" indicate a solid hull. "Dull" sounds indicate possible voids or soft core. The sound of the hull can vary by hull thicknes and cored versus non cored. So the bottom of the C-Dory will sound different than the sides.
 
Ball peen can and will injure the gel unless you are a REAL expert. The clear plastic hammer heads or "dead hit" type plastic hammers may be a better choice for amateur hammer wielders. I suppose if you taped the flat head of the peen hammer with tape you might be safer than whanging way with just the exposed metal head.
 
Given that the sides of the C-Dory hull are pure fiberglass, it's hard for me to imagine that there is much you can learn from banging on them with a hammer. As for the cored area, I think you'll get a much better understanding of what is going on with a moisture meter than a hammer. So my suggestion was that the best hammer for your purpose is none and use a moisture meter in the areas most likely to have problems - the transom and the cored sections of the hull near current or past potential penetrations.
 
Tapping out a hull can be done just as well with a plastic screw driver. You can use a plastic hammer, as Potter Water suggests. Agree that you are very unlikely to find any delam on the sides of a C Dory. For the dec, a screw driver or plastic hammer. I do not agree on a ball peen hammer. It may be OK in some surveyor's hands, but unless you have a lot of experience it can be destructive if there is a void in the gel coat or serious delimitation.

Moisture meter on the transom and bottom. Hard to tap out the bottom of a boat on a trailer, because of the bunks. But you can do the deck and transom. Most of the boats will be fine, without delimitation.
 
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