A different way to learn to sail.

Preparing for the French boating licence means connecting rules to situations on the water. A vessel’s lights depend on the viewing angle. Tides change available depth. Anchoring requires an understanding of the seabed and room around the boat.

Poseidon uses these situations as a starting point for learning. Learners explore a scene, change a parameter and observe the result, then turn to the explanation and related questions. The purpose of 3D is to make a rule observable and give meaning to an answer.

Most of Poseidon’s content is unlocked through in-app purchases.

A static diagram chooses a viewpoint for the learner. An interactive scene lets them ask a question: what would I see from the other side of the vessel? How much room remains under the hull as the water drops? Where is the channel relative to my approach? Moving the camera becomes a way to reason about space.

I build scenes around what needs to be understood. Light sectors, day shapes, terrain and the waterline provide reference points. A cutaway reveals the seabed; switching from day to night changes the available cues. The challenge is to keep the object, environment and rule consistent with one another.

The visual work also serves readability: recognisable silhouettes, contrast, water materials and framing. Realism supports observation, with deliberate simplifications to isolate a concept. These scenes are learning aids, not a validated navigation simulator.

Metal is Apple’s graphics and compute API. It lets an app directly prepare work for the graphics processor, or GPU. In Poseidon, Swift manages exercise state and interactions; Metal renders scenes from that state. Moving the camera or changing conditions updates the data sent to the renderer, then the next image.

The main maritime scenes use procedural rendering. A triangle covers the screen and its shader reconstructs the scene for each fragment. From the camera, a ray advances through shapes described by distance functions until it meets a surface: this is ray marching. The renderer then calculates materials, lighting, reflections and water refraction. Terrain, vessels and sea can respond to the same scene parameters.

Metal provides precise control over calculations, resources and resolution, while allowing shaders to be reused across Apple platforms. This choice also means building and maintaining a renderer, monitoring its cost and adapting it to devices. Smoothness depends on the work done for each frame, not merely on the choice of API.

Per-pixel rendering becomes more expensive as resolution increases. The renderer measures actual GPU time and compares it with the frame budget. When rendering takes too long, it reduces scene resolution and may lower the target frame rate. Quality can rise again when enough headroom returns. Text and controls remain in the native interface.

The renderer also limits pending frames to avoid accumulating input lag, and pauses its rendering loop when the view moves into the background. These choices balance readability, responsiveness and computational load. Configured frame rates are targets, not substitutes for measurements on each device.

The iOS, iPadOS, tvOS and visionOS versions use the same native codebase. Content models, rules and exercise logic are shared. SwiftUI provides common interface components; Metal is used for the educational scenes.

The aim is to evolve the learning experience in one place. A corrected rule or improved lesson benefits the foundation of all four versions. Platform-specific work focuses on presentation, controls and system integration. Shared code still needs verification in each device context.

The ambition is to help learners explain a choice in context and identify the relevant rule when conditions change. Lessons, exploration and mock exams form the steps of this approach.

This is an experiment in product design and learning. Better understanding or higher exam pass rates still need to be assessed with learners. Shared code supports iteration while preserving the ways each platform is used.

Technical references in Apple’s documentation: Metal · Resource fundamentals · Setting up a command structure.

Buoys come to life, crabs become captains and nautical expressions find their way into conversations. Here is a selection of Poseidon’s stickers, bringing a little humour to the world of the app.