I'm ever surprised when I see someone recommend the dog chain corkscrew anchors for tying down a boat....I'm sure they wouldn't even hold my (large) dog if he seriously resisted. At our club, we use the auger anchors that are made for tying down mobile homes. They're maybe two feet long with about a three-quarter inch diameter shaft and a four inch or so diameter auger portion at the lower end. You have to use a tire tool or such to screw-drive them in. They'll probably work in anything but sand. We've never had one fail to hold, including reported 70 mph straight line winds and 60-80 mph winds sustained for hours during Katrina. Getting everyone to keep their tie-down straps/lines in good, tight condition is another story....

Jerome Vaughan
Hobie 16 102614
Clinton, Mississippi