A simple model of a boat, and what it leaves out.

What is modelled

• Moving through the water: forward, sideways and turning motion, each with its own resistance. Sideways resistance is far larger, which is why a boat carves a turn instead of sliding.
• Thrust and gear: the lever has a neutral band in the middle. Out of it the engine is in gear at idle (about 2 knots ahead when it settles), and further out it gives more power. Astern gives about 60% of the thrust ahead.
• Steering: outboards and sterndrives point their thrust (up to 30 degrees); inboards have a rudder (up to 35 degrees) that works on the propeller's wash and on the water flowing past. The helm takes about 1.2 seconds lock to lock.
• Prop walk: single engines have a right-hand propeller; astern, the stern walks to port.
• Twin engines: two levers; one ahead and one astern turns the boat nearly in place.
• Wind: force on the topsides grows with the square of the wind over the boat. It acts a little forward of the hull's own resistance, so a stopped boat's bow blows off downwind.
• Current: the water moves and the boat moves with it. Speed in the readout is over the ground.
• Contact: the hull is tested against every dock, pile and boat. A contact is measured by the speed at which that point of the hull was closing on the obstacle.

What is left out

• Waves, wakes from other boats, shallow water and the way a hull squats or lifts.
• Gusts: the wind is steady.
• Lines, fenders, crew, cleats and spring-line techniques.
• Your boat. Real boats of the same length can handle very differently.

The score

Start at 100. Take off 5 for each soft touch (closing speed under 0.30 m/s), 20 for each hard one, 1 for every 5 seconds over the drill's par time (at most 20) and 1 for each shift over par (at most 10). A shift is each time an engine goes into gear. A run that leaves the yard or runs past four times par scores 0.

Berth drills finish when the whole hull is inside the dashed box, pointing the right way, moving slower than 0.15 m/s, and stays that way for two seconds. Exit drills finish when the boat passes the gate bow first. The mooring finishes when the bow is within 1.2 m of the buoy at 0.35 m/s or less, heading within 35 degrees of the wind.

When you save a run, our server checks that the measurements (time, shifts, touches) are in range and works the score out again itself; a score typed into the form is ignored. The measurements come from the simulator in your browser, so a logbook is a private record for you, not a verified result; there is no public leaderboard.

The demo, and how we know each drill can be done

The boat on the home page is steered by a small autopilot in the same script. The site's tests run that autopilot on every drill at the drill's own wind and current: each of the nine drills is finished with no hard touch by at least one boat, each of the four boats finishes several drills, and the three free drills are finished by the free 20 ft outboard. A release cannot ship if any of those runs fails.

The "Watch a demo run" button on a drill appears only for a boat the tests have proven on that drill, at the drill's own conditions. The autopilot is not a perfect skipper: some boats, and stronger wind or current you set yourself, make a drill harder than anything it has been tested on.