Depends more on what's on the bottom than anything else. The American Boat and Yacht Council tables recommend 225 lbs of holding power for a 35ft boat in 15knts of wind. You can get that with a 5lb danforth IF your dealing with sand and mud, but if you throw a grassy bottom into the works then your gonna need more.Of course, a 5lb Danforth is so small it would look kind of silly. You know, a 15 lb Danforth with a few feet of chain would give you less than 20 lbs to haul up after a good lunch, and would be useful for kedging if you run aground, as a secondary in high winds, and is still fairly easy to stow.