Bimaru — Free Ship-Finding Logic Puzzle for Kids 7–11
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Bimaru — the battleship puzzle — is solved with your head, not with luck. A fleet is hidden in a grid. Nobody shoots at it. Instead you are told two things: the numbers along the top and the side say how many ship squares sit in each column and each row, and the shape of the fleet is printed beside the board. From those numbers alone the position of every ship can be worked out.
90 levels, each proved to have a single answer
Every level was built and then checked twice — once by constraint propagation, once by counting solutions exhaustively — so that exactly one arrangement of the fleet satisfies the numbers. That guarantee matters more than it sounds: it means a child never has to guess and hope. If the answer is not visible yet, the information for it is still on the board somewhere.
Three sizes, three depths of thinking
Thirty levels are 6×6 with a small fleet, thirty are 8×8, and thirty are the full 10×10 board with the classic ten-ship fleet: one four-square ship, two of three, three of two and four single squares. Within each size the levels get harder in a measured way — the starting hints thin out, so on the last 10×10 levels there are only about five given squares instead of ten.
Water is half the answer
The trick beginners miss is that marking water is as much progress as finding a ship. A row whose number is already satisfied is water all the way across; the squares diagonally touching a found ship are water because ships never touch, not even at a corner. The game has a button that floods a finished row or column with water in one go, so the bookkeeping never gets in the way of the thinking.
How to play
Tap a square to cycle it: empty, then water, then ship. Long-press on a tablet — or right-click with a mouse — to cycle the other way. When a row or column already has all its ship squares found, press the flood button and the rest of that line fills with water. The check button tells you whether the board as it stands agrees with the numbers. The rule is explained aloud the first time you open the game, and after that the voice reads the task and reacts to what happens, without commenting on every tap.
What your child learns
Deduction as opposed to guessing — the difference between a ship could be here and a ship must be here. That is the whole skill, and this puzzle makes it visible: every conclusion follows from a number on the edge and the squares already known. Underneath it there is steady counting to ten and twenty, and a lot of practice at holding two constraints in mind at once, since a square belongs to a row and a column at the same time. There is no arithmetic to perform beyond counting, and nothing here is timed.
The science behind the games
Every Dad4Kids game is built on one simple truth: children want to play, not study — so we turn learning into a game worth replaying. The method draws on peer-reviewed research in game-based learning, motivation, and how memory works.
- Prins et al. (2013). “Braingame Brian”: toward an executive function training program with game elements. Games for Health Journal.
- Tokac et al. (2019). Effects of game-based learning on students' mathematics achievement: A meta-analysis. Journal of Computer Assisted Learning.
- Alotaibi (2024). Game-based learning in early childhood education: a systematic review and meta-analysis. Frontiers in Psychology.
- Lampropoulos & Sidiropoulos (2024). Impact of gamification on students' learning outcomes and academic performance: a meta-analysis. Education Sciences.
- Taylor & Boyer (2019). Play-based learning: evidence-based research to improve children's learning experiences. Early Childhood Education Journal.
- Gottfried (1990). Academic intrinsic motivation in young elementary school children. Journal of Educational Psychology.
FAQ
How do you solve a ship-finding puzzle?
Start with the extremes. A row whose number is zero is water all the way across; a row whose number equals its length is ship all the way across. Fill those in, then mark water diagonally around every ship square you know — ships never touch, even at corners — and look for a line where the remaining unknown squares exactly match the number still missing.
What is this kind of puzzle called?
Bimaru, from the Japanese puzzle publishers; English-language puzzle books usually call it a solitaire fleet puzzle, and it descends directly from the pencil-and-paper naval game everyone plays at school — which in shops is sold as Battleship. The difference is that here nothing is fired: the fleet is deduced from numbers, and one player solves it alone.
Do ships touch each other?
Never — not side by side and not corner to corner. Every ship is surrounded by water on all sides, and that rule does at least as much of the solving as the numbers do.
What is in the fleet?
On the large 10×10 boards it is the classic ten ships: one of four squares, two of three, three of two and four single squares. Smaller boards use smaller fleets, and the fleet is always drawn beside the grid so you can tick off what you have already found.
Is there always one answer?
Yes. Each of the 90 levels was verified by solver to have exactly one valid fleet placement, so guessing is never required and never rewarded — everything can be reasoned out from the numbers and the water.
Does it work on a tablet?
Yes, and tapping suits it well: one tap adds water, another turns it into a ship. Long-press steps backwards through the same cycle when you change your mind.
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By Evgeny Arsentiev, PhD · Last updated: September 2026