My Columbia 36 was about the same, the sides I could see had about 3" of foam but can't tell about the hull side or the bottom. The hull was dark green and late in the day when the sun would shine on that side of the hull the icebox temp would rise, so Im thinking there wasn't much there if any. I added six layers of half inch insulation board (the pink or blue stuff used in houses) to give 3 inches. Had to use layers to conform to the curve, if it was flat I could have used one thick layer. Did the same to the bottom too. Covered that with 8oz glass and epoxy. Big job but it worked, the box stays cold now. Box is a little smaller now, but my fridge conversion unit was too small for the original size anyway.