It isn't a ground but actually part of the aerial system and it doesn't need to be connected to the main ground in fact I advocate keeping it separate in my books, as long as the ground component i.e. ground plate or whatever is adequate for signal transmission. In general they don't have a track record in boats as causing corrosion, personally I wouldn't connect this and make sure you get best performance with the ground. Answer is don't run a wire from large surface area ground, no point, no advantage to you
