M_Boats: Water Line

I haven't found anything in the archives on this. Has anyone found a good way to mark the water line when applying bottom paint on an M-15 ? The 17s seem to have a stripe at the waterline already in the mold. I had a "professional" do my M-15 the first time it got bottom painted and I've had to live with the results ever since. I've tried adjusting the painted line to the real water line when I've repainted but haven¹t been able to get it right. It might work if I stowed jerry cans of water in strategic places on the boat to make it conform to the painted waterline but there has got to be a better way. Any suggestions would be appreciated. Stan Winarski M-15, #177, Carol II Stan Winarski M-15, #177, Carol II