Hi, just reading the Huge ships rulebook and was wondering with precision shot effect , does the attacking ship need to be wholly in the specified arc or can it be partially in?

Partially will do. Just like how a ship at range 2 doesn’t have to be entirely at range 2. Part of it could hang into range 3, or part could be outside the firing arc.

I have had the same question. And every time I do, I ask myself, "Can a ship ever be fully inside another ship's bullseye arc?" And then I laugh and remember that a ship can always be partially in a specified arc (I mean, unless it explicitly says otherwise).