Hey, John.. The area around the mast base has an overlay of maybe 1/2" then under that is an aluminum plate that is , I think, about 1/4 inch thick. Best is to drill and tap into the plate to hold the pad eyes.. The plate is all over that raised area under the mast. It extends to close to the edge of the raised area.. Through bolts aren't really an option because you can't easily get at the underside of the plate. Here is a shot of the area and the pad eyes on my 34..
Those two small ones are for the reefing lines, and I think were original to the boat
