My understanding of Voronoi is that its goal is to determine the areas that are closest to some positions and I am not sure how it would help in this game.
A simple floodfill with a move depth of 1 should be enough for acceptable pathing (at least until silver league).
Here is an example:
x: visited cells or islands
o: sea cells that are not visited
p: your current position
The algorithm is quite simple, for every every new cell you can reach, compute its accessible zone (cells that are linked to it by non visited sea cells), then choose the one with the biggest zone:
_N (0,2): 6
_E (1,3): 1
So here your best move is N.
In some edge cases you can make wrong decisions, but it’s marginal (and if you really want to you could compute the accessible zone after n moves instead of just 1):
So N seems to be the better option, but then your zone will be cut in 2. In the end you will only get 4 moves while W and S would have given you 5 moves. => this doesn’t arrive often.
My experience is that you won’t often surface more than once per game with by computing the accessible zones with a move depth of 1. Also most of the time the game will end before you even surface when at least one player has good opponent detection. (I think there is no silence in wood?)