Of course if I were doing this on a boat I would have first pre-taped over the holes, like the photo above, & then used my countersink bit between my fingers to remove the tape from the holes. This method protects the deck and the countersink carves out a nice clean hole in the tape.
In this photo I simply used a rag with Acetone to wipe away any over flow. Use tape and it will go much smoother and cleaner. I simply forgot when photographing this..