Lucas McCain

I believe it's pre-1980 because I saw it when I was younger but it was about a boy that went to live with his grandpa (Ned Beatty I think) and was somewhat disconnected from him but he became friends with the grandpa's old dog and it was a semi boy/dog movie but they were always trying to catch a fish named Moby Dick in a local pond, the grandpa gave the boy a pen knife, got tired of the dog because it was old and threw it in the pond with a rock tied around its neck and the kid dove in, used his pen knife to cut the rope and saved the dog.
I have looked on IMDB at Ned Beatty's movie list and I can't seem to find it so it might not have been him. I ovbviously remember many things about it and I would like to see it again. Anyone even remotely know what movie this might be?

Windbreaker

All I can think of is Debra K. Beatty, who starred as Pleasure Unit #2 in the 1994 smash hit CYBORG 3: THE RECYCLER.