Boat castle (funagakoi)

How it is built

From 5i the king steps to 6h and then 7h, just two moves. The left gold stays on 6i, the right gold moves from 4i to 5h, and the right silver often comes to 4h. The left silver remains on 7i and the bishop on 8h, both next to the king.

Strengths and weaknesses

Speed is the whole point. Against a Ranging Rook player settling into a Mino, the Boat castle lets Static Rook start a rapid attack, such as the Right Fourth-file Rook, before the opponent's position is fully ready. The cost is thin protection from above and along the diagonal: no gold or silver stands in front of the king, and White's bishop on 3c, aiming down the long diagonal toward 7g and 8h, needs constant watching.

Upgrading it

If the game slows down, the Boat castle should be reinforced. It is also the usual starting point for an Anaguma: once the bishop and lance make room, the king continues to 8h and then into the 9i corner.