I bought a used fiberglass sailboat. It has a 7/8" drain plug that is missing the stopper. I can't find any 7/8" plugs, so I am going to replace it with a 1" plug. That obviously requires me to enlarge the existing hole. On a drill press that would be easy, but getting the sailboat on my drill press would be tough.

I have two ideas...
1) Draw a 1" circle over the existing hole and enlarge it with a multitool. My experience is that multitools are not particularly precise, so I m reluctant to do this.
2) I have a cove router bit that has a full diameter of 1". Put in a drill, it should self center in the 7/8" hole and then enlarge it to 1". Or maybe not.

Comments or other ideas would be appreciated.

Or, I could fiberglass over the existing hole and put a new one elsewhere. I have a brad point carbide 1" drill.