The object of the game is to form groups of islands linked by bridges. An island is exactly four orthogonally adjacent tiles of your own colour. Any fewer adjacent tiles are a sandbank.
The first player places two light tiles anywhere on the board. They may be adjacent or separate.
The second player chooses either to adopt this move and play using the light tiles, or to place two dark tiles and play using those.
Each player takes turns to place either two tiles or one bridge.
Tiles can be placed anywhere on the board, either adjacently or separately, provided that:
- they are not placed under bridges
- no tile is adjacent to an island of the same colour, even diagonally
A bridge can be placed between two tiles of the player's colour that are two spaces from each other orthogonally or diagonally, or at a knight's move. The centre of the bridge must be over water, not any tile. Only one bridge can begin or end on any tile. Bridges may not cross each other.
Game end is triggered when either player is unable to place two tiles and chooses not to (or is unable to) place a bridge. (The player using dark tiles gets opportunity to take an equal number of turns).
The players score each group of islands connected by bridges (including connections via sandbanks) according to a rule of triangular numbers:
|Number of connected islands||1||2||3||4||5||6 ...|
In the case of a tie, the player with the most islands is the winner. If still tied, then the player with the most bridges is the winner.