I hunted the land and the beaches of Southern NJ for years witha MArk I without any problems. Like you I ground balanced in the dry sand and then proceeded to hunt the wet sand. I would set the discrimination to just above iron and would have to lower the sensitivity to a little below the preset and it worked fine and I was able to dig coins and ring to 6 or 7 inches with the 7 1/4 inch coil. If I remember correctly the Mark I is only a two filter machine and as such will lose depth in a highly mineralized environment. If New Yorks Beaches are as mineralized as you say you may need to switch to a multifrequency detector or possibly even a PI as these machines work quite well in the wet salt sand and finding coins and rings to depths of a foot or more.