Safe WaterSafe Water

• Tap a square to sweep it. A number tells you how many mines sit in the eight squares around it.
• The sweeper works outward from the entrance: it can only sweep a square next to water you have already swept.
• Right-click a square, hold it down on a touch screen, or pick the Buoy tool to mark a mine. Buoys are free.
• Tap a number once all its mines are buoyed to sweep every other square round it in one run.
• Ships wait outside for a while, then give up and go to another port. Once a lane of swept squares reaches their berth, they come in by themselves and pay the port.
• Spend what they pay in Build: the fish market, the container crane, the ferry terminal, a second sweeper, a second fuel line, an ROV or a dolphin team.
• Open all four berths to unlock the next port. There are five, and each one has more mines and ships that wait less and call more often. Each port has three stars: no strikes, no ship turned away, and the port open in time.
• A mine sends the sweeper to the yard for 12 hours and costs $25,000 of repairs.
• Some squares hide old things on the seabed. Sweep them to add them to your logbook. In the port, the town museum pays for them.
• Every square can be worked out from the numbers, so you never have to guess.

The harbour, the ships, what they pay, how long they wait and what the rebuilding costs are made up for the game. So are the dolphin team's price, how long a search takes and how long they rest, and the finds on the seabed and what the museum pays for them. The numbers are a game too: real sonar gives the crew contacts to check, not a count. The notes that come up while you play are real, and each one links to where it comes from.