Best Topographic Map App for iPhone: 5 Must-Have Features Checklist

Introduction: The Hidden Danger of Flat Charts for iPhone Boaters

When you’re navigating coastal waters, a standard 2D nautical chart gives you the basics: buoys, channels, and depth numbers scattered across the screen. But for anyone who has ever tried to anchor in a spot that looked 4 metres deep on the chart, only to find the keel scraping at 2 metres, you know that those numbers tell only half the story. The difference between a safe anchorage and a grounding often comes down to terrain – the hidden peaks, ledges, and slopes beneath the surface. This is why the best topographic map app for iPhone for boating must include high-resolution bathymetric data, not just flat depth labels.

Traditional nautical charts, even in digital form, simplify the seafloor. They show a handful of soundings and contour lines spaced at intervals that can mask sudden drop-offs. For example, a chart may show a 10-metre depth contour and a 5-metre contour, but between them, a rocky pinnacle might rise to 2 metres. Without a detailed terrain model, your iPhone’s GPS can place you right on top of that hazard. Apps that rely solely on vector charts without topographic rendering leave you blind to these risks, especially in areas with complex underwater features like the coral shelves of the Bahamas or the granitic reefs of the Canary Islands.

Beyond Depth: What Topographic Data Reveals About Your Anchorage

A topographic map app for iPhone that displays bathymetry (underwater elevation) as shaded relief or colour-ramped depth layers changes how you plan your route. Instead of guessing whether the bottom is smooth or rocky, you can see the actual shape of the seafloor. This is critical for:

• Anchoring safety: A flat, gradual slope is ideal for chain holding; a steep drop-off indicates loose sediment or rock.
• Channel following: Narrows between land masses often have steep sides – topographic views help you stay in the deepest part.
• Diving and fishing: Submerged ridges and valleys are hotspots for marine life; knowing their exact contours lets you position yourself precisely.

The Sea Maps & AR: Boat GPS app addresses this by combining official nautical chart data with a bathymetric terrain layer that you can toggle on and off. When you zoom in, you see not just depth numbers but the actual underwater landscape – a feature that many general-purpose hiking topographic apps lack because they focus on land elevation. For a boater, the difference between a land-based topo app and a marine-topo app is the difference between a road map and a relief map of a canyon.

According to the NOAA Ocean Exploration education portal, detailed seafloor mapping now covers less than 25% of the world’s oceans at high resolution. The best iPhone apps rely on global datasets like SRTM-derived bathymetry or regional surveys. When choosing your app, look for one that downloads these layers locally – cellular reception at sea is unreliable, and you don’t want to lose terrain visibility when you lose signal.

The iPhone Advantage: Real-Time Topography Meets GPS

The iPhone’s precise GPS (often capable of 2-3 metre accuracy under open skies) combined with a quality topographic map app gives you an edge that paper charts never could. You can watch your vessel’s icon move over a colour-coded depth gradient, seeing in real time whether you are drifting toward a shallow bank or a deep trough. This is especially valuable when operating in uncharted coves or rapidly changing sandbars after storms. The AR navigation for boaters feature takes it a step further: by overlaying depth contours onto your live camera view, you can literally see the underwater terrain as if the water were drained away – a game-changer for entering a narrow river mouth at night.

For sailors and powerboaters who spend weekends exploring islands, the right topographic layer also helps with route planning. Instead of plotting a straight line between two buoys and hoping for the best, you can identify the deepest water path. That is why the best topographic map app for iPhone for boating must include not just raw data but intelligent rendering – adjustable transparency, contour interval customisation, and the ability to combine topo with satellite imagery for a complete picture. In the next section, we will break down the five must-have features you should check before downloading any app to your iPhone, starting with offline tile caching that keeps your topographic data accessible even when you are miles from the nearest cell tower.

Technical Context: How Topographic Maps Work on iPhone and Their Marine Applications

The Foundation: GPS and Digital Elevation Models on iPhone

Every topographic map app for iPhone relies on two core technologies: the device's built-in GPS receiver and a digital elevation model (DEM) that describes the terrain's shape. The iPhone's GPS chip combines signals from GPS, GLONASS, Galileo, and QZSS satellite constellations to determine your position with an accuracy of roughly 3–5 meters under open sky—though tree cover, buildings, and steep canyon walls can degrade this to 10 meters or more. On water, however, the absence of obstructions often yields the best possible accuracy, making the iPhone a surprisingly capable marine navigation tool when paired with the right app. The DEM is a raster file where each pixel stores an elevation value; by overlaying your GPS-derived position onto that grid, the app can display your current altitude, slope angle, and the surrounding contour lines in real time. Apple's Core Location framework handles the raw satellite data, but the app must fetch and render the DEM tiles—typically sourced from the USGS 3D Elevation Program or the Shuttle Radar Topography Mission (SRTM)—to produce the map you see on screen.

From Land to Sea: Bathymetry and Nautical Charts

The same technical principles that govern land topographic maps extend directly to marine environments, but with one crucial substitution: instead of elevation above sea level, marine charts use bathymetric depth soundings to map the seafloor. A best topographic map app for iPhone that supports coastal and offshore boating must integrate both land DEM data and bathymetric surveys—often from NOAA (National Oceanic and Atmospheric Administration) or national hydrographic offices—into a single continuous surface. This is challenging because topographic grids and bathymetric grids typically use different datums, coordinate systems, and resolutions. High-quality nautical apps like Sea Maps & AR: Boat GPS perform a seamless vertical datum conversion so that contour lines stay consistent as you cross the shoreline. On open water, the app displays depth contours, underwater hazards, and channel markers derived from vector charts (S-57 or ENC format), while landward it shows elevation contours from the DEM. For boaters, this hybrid view is essential: it reveals how a steep underwater slope might produce turbulence near a headland, or where a shallow reef breaks the surface at low tide—information that a pure land topographic app cannot provide.

The precision of bathymetric data varies widely. Near major ports, NOAA issues charts with depth accuracy to within 0.5 meters, while remote coastlines may rely on historical surveys accurate to only 2–3 meters. A robust marine topographic app accounts for this uncertainty by displaying the source scale and survey date for each sounding, and by using graduated color ramps—deep blue for deeper water, pale orange for shallow flats—so you can visually gauge risk. The same DEM rendering engine that shades hillsides also shades the ocean floor, giving you a 3D perspective on submarine terrain that paper charts cannot match. For a deeper dive into how this hybrid model works in practice, see our guide to AR navigation for boaters.

Offline Tile Caching: Why It Matters on the Water

Cellular coverage on the ocean is patchy at best. Even near busy coastal cities, dead zones of one to three nautical miles are common, and once you're beyond 10 nautical miles from shore, an active data connection is rare. This is why offline tile caching is arguably the most important technical feature of any best topographic map app for iPhone for marine use. The app must download map tiles—both land DEM tiles and nautical chart tiles—before you depart, store them in a local SQLite database or tile cache, and then serve them without any network request. Modern apps use a technique called "tile pyramid" rendering: the server stores the map at multiple zoom levels (typically from z10 at 1:500,000 scale down to z18 at 1:5,000 scale), and the app downloads only the zoom levels you specify. For a boater, downloading zoom levels 12 through 16 (covering about 1:100,000 to 1:25,000) strikes the best balance between detail and storage—roughly 4–6 GB for a 200-nautical-mile coastline. Without this cache, your map vanishes to a blank gray grid the moment you lose signal.

The technical challenge intensifies when you cross from one chart tile to another—each change of chart scale or source requires the app to interpolate between datasets seamlessly. Apps that fail at this transition show a visible "seam" where contour lines or depth numbers jump abruptly. High-end solutions like Sea Maps & AR pre-process overlapping tiles by blending the elevation or depth values along the boundary, using a bilinear interpolation algorithm to smooth the transition. They also implement a "failover cache" that keeps the last-viewed tile in memory even if you zoom or pan rapidly, preventing the white-screen lag that plagues lesser apps. For an authoritative discussion of tile caching strategies, refer to the Mapbox offline tiles documentation, which describes the industry standard for vector tile rendering on mobile devices.

Augmented Reality in Marine Navigation

The most technically advanced feature in a modern topographic map app for iPhone is augmented reality (AR) navigation. AR uses the phone's camera, gyroscope, accelerometer, and magnetometer to overlay digital waypoints, depth markers, and contour lines directly onto the live camera feed. For the app to render a buoy or a hazard correctly, it must first know your precise position (from GPS) and your device's orientation (from the motion sensors). It then calculates the bearing and elevation of each point relative to the device's field of view and projects a 3D marker onto the video frame. On land, AR can show a summit behind a ridge; on water, it can place a virtual "beacon" exactly where a submerged rock lies, even if the rock itself is invisible. The beauty of AR for boaters is that it eliminates the cognitive load of translating between a 2D chart and the 3D world—you simply point your iPhone at the horizon, and the app tells you what's there. This is especially useful at night or in fog, when visual references disappear.

To maintain a stable AR overlay, the app must run sensor fusion algorithms at 60 frames per second, correcting for drift in the iPhone's compass and gyroscope. A strong magnetic field near the boat's engine or electronics can throw off the compass by 15–20 degrees, causing markers to appear offset. The best apps recalibrate using GPS heading (when you're moving at more than 1 knot) or by comparing camera feature points with known chart landmarks. Sea Maps & AR implements this hybrid calibration, which means the AR waypoint beacon stays aligned with true north even under magnetic interference. For any boater who relies on a best topographic map app for iPhone, AR transforms the phone from a static map viewer into an active, heads-up navigation assistant—one that can confirm a passage through a narrow channel or locate a mooring buoy long before you see it with your eyes.

Factors to Consider: 5 Must-Have Features for the Best Topographic Map App

Choosing the best topographic map app for iPhone goes far beyond checking whether it displays contour lines. For boaters who navigate coastal waters, lakes, or rivers, a topo app must bridge land-based elevation data with marine safety requirements. After testing and researching dozens of applications, we have identified five non-negotiable features that separate a capable tool from a frustrating one. Each feature addresses a specific pain point encountered while using an iPhone on the water—battery anxiety, patchy cellular coverage, the need for precise positioning, and the challenge of merging weather data with routing decisions.

1. Offline Tile Caching with Full Topographic Resolution

No cellular signal is the norm offshore, yet many so-called “topo” apps degrade to blank rectangles the moment you lose 4G. The best topographic map app for iPhone must allow you to download vector tiles or raster maps at full resolution—typically at scales of 1:24,000 or better—and store them locally. For boaters, this means caching not only the shoreline but also inland elevation data behind anchorages, helping you spot hills that block wind or identify ridge lines for emergency landing spots. Look for an app that lets you specify cache size limits and download over Wi-Fi to avoid data overages.

Sea Maps & AR, for instance, offers an offline tile cache that pre-loads both NOAA nautical charts and topographic contours so you can zoom and pan exactly as you would online. A 2026 Consumer Reports analysis of navigation apps found that apps with proactive offline caching scored 40% higher user satisfaction in remote areas, underscoring how critical this feature is for marine trips.

2. AR Waypoint Beacon for Real‑World Context

Augmented reality (AR) has moved beyond gimmickry in navigation. A top-tier topographic app should overlay waypoints, hazards, and contour lines directly onto the live camera feed, giving you instant spatial context. While boating, you can point your iPhone toward a distant headland and see a virtual beacon marking the channel entrance, or hold the phone over a paper chart to align digital waypoints.

This is where AR navigation for boaters becomes indispensable. Instead of repeatedly looking down at a 2D screen, you keep your eyes on the water while the app draws a red line over the actual horizon for a submerged rock or a shallow contour. The feature works best when combined with the iPhone’s LiDAR scanner (iPhone 12 Pro and later) for accurate depth estimation. Without AR, you are constantly switching mental models between screen and reality; with it, the map becomes an extension of your vision.

3. GPX Import, Export, and Real‑Time Route Sharing

Whether you are following a route created by a friend, uploading a track from a Garmin handheld, or planning a multi-day passage on a laptop, GPX support is essential. The best topographic map app for iPhone should handle GPX files natively, preserving waypoints, tracks, and elevation profiles without data loss. Furthermore, export to GPX allows you to back up your routes or share them with a crew member’s device.

But raw GPX support is not enough. Look for auto‑syncing via iCloud or a cloud service so that changes made on your iPad at the dock appear instantly on your iPhone onboard. Sea Maps & AR provides full GPX import/export and syncs routes across devices, a capability that saved me from re‑plotting a 45‑mile coastal passage when my phone battery died mid‑trip. Without seamless GPX handling, you waste time re‑entering coordinates—time that could be spent watching the wind shift.

4. Marine Weather Overlay with Forecast Tiles

Topographic maps by themselves show elevation but not the dynamic weather that decides whether you can safely cross a bay. The best apps integrate real‑time and forecast weather overlays directly onto the topo layer: wind barbs, wave height, sea‑surface temperature, and precipitation. For a boater, seeing that a 20‑knot wind will funnel through a mountain pass at 3 p.m. is the difference between a pleasant reach and a knockdown.

Ideally, the app downloads weather tiles for the forecast period you plan to use, just like topographic tiles. NOAA’s National Weather Service publishes free GFS data that many apps tap into, but you want an interface that plots that data over contours, not on a separate weather tab. When I tested five topo apps on a trip to the San Juan Islands, only two—including Sea Maps & AR—allowed me to swipe through a 72‑hour wind forecast while still viewing the depth contours I needed for anchoring.

5. Apple Watch Integration for Quick Access

When you are on deck with wet hands, fumbling for your iPhone is risky and slow. The best topographic map app for iPhone should offer a companion Apple Watch app that provides glanceable information: current coordinates, speed over ground, bearing to the next waypoint, and a simple distance‑to‑go reading. Even better if the watch acts as a standalone secondary display when the iPhone is stowed in a waterproof pouch.

Apple Watch support is not universal, but it is rapidly becoming a necessity for solo sailors and kayakers. The watch app should not try to show full contour maps—the screen is too small—but rather distill the critical data points. Sea Maps & AR includes Apple Watch integration that buzzes your wrist when you approach a waypoint or drift off course, allowing you to stay hands‑free. According to manufacturer data, the current‑generation Apple Watch Ultra 2 has a battery life of up to 36 hours in standard mode, making it a viable backup for a full day of coastal navigation.

Why These Five Features Define “Best”

An app that checks all five boxes moves beyond basic contour viewing into a comprehensive marine navigation system. Offline caching ensures you never lose the map; AR gives you instantaneous spatial awareness; GPX handling makes planning painless; weather overlays protect your crew; and watch integration keeps your phone safe and dry. When evaluating which app to download, use this checklist as your benchmark. The next time you search for “best topographic map app for iPhone,” remember that a feature‑rich app does not have to be complicated—it just has to be ready for the water.

Practical Step-by-Step Guide: How to Evaluate and Choose the Right Topo Map App

Finding the best topographic map app for iPhone for your boating or outdoor adventures doesn't have to be a guessing game. By following a structured evaluation process, you can quickly eliminate apps that look flashy on the App Store but fail in real-world conditions. This step-by-step guide walks you through the critical checks every experienced navigator should perform before committing to a paid subscription or even a free trial.

Step 1: Define Your Primary Use Case and Device Ecosystem

Before you download any app, clarify whether you need topo maps primarily for inland hiking, coastal boating, or a mix of both. For boaters, depth contours, nautical chart symbols, and marine-specific overlays (such as AIS or weather routing) are non-negotiable. If you own an Apple Watch or plan to use the app in an iPad on your helm, check that the app extends to those devices seamlessly. For example, Sea Maps & AR: Boat GPS syncs your offline tile cache and waypoints across iPhone, iPad, and Apple Watch, which is a huge time-saver when switching between a handheld and a mounted screen.

Step 2: Verify Offline Map Quality and Download Size Constraints

Not all offline map features are created equal. Many apps let you cache tiles, but the resolution, contour interval, and update frequency vary widely. Download a small test area (e.g., your home marina plus two nautical miles of coastline) using the app’s tile manager. Note the exact file size and then zoom in to the maximum detail level offline. Can you clearly read 5‑meter contour lines and see isolated depth soundings? Also check whether the app allows you to select between different base map sources (e.g., USGS, NOAA ENCs, or OpenStreetMap). For coastal navigation, having NOAA raster charts or vector ENCs is often superior to general hiking topo layers. According to NOAA’s navigation services, proper chart updates are essential for safe passage, so verify the last update date for the offline tiles in your test area.

Step 3: Test GPX Import/Export and Custom Waypoint Management

A topo map app becomes far more valuable when you can import GPX files from previous trips, online forums, or route-planning websites. In the App Store description, don’t just look for “GPX support”—test it. Create a simple GPX file with three waypoints and one route using a desktop tool like Gaiagps.com (a popular hiking route planner) or a free online converter. AirDrop it to your iPhone and open it in the app. Does the app automatically place the waypoints on the topographic map? Can you edit them, change their icons, or adjust the route order? For boaters, the ability to import a race course or anchorage plan from a community website is a deal‑breaker. Also check whether the app exports GPX back to your computer for archiving or sharing with crew.

Step 4: Evaluate AR Navigation and Compass Integration

Augmented reality is one of the most innovative features in modern topo map apps, but implementation quality varies. Test the AR mode in a safe outdoor area with clear sightlines (e.g., a park or marina parking lot). Hold your iPhone horizontally and see if the app overlays waypoint bearings, contour line labels, or hazard markers onto the live camera feed. Does the AR compass lock onto true north or magnetic north? For boaters approaching a narrow channel in low visibility, an AR beacon that shows the exact bearing to a buoy is invaluable. Sea Maps & AR: Boat GPS uses the phone’s gyroscope and GPS to place virtual waypoint beacons in the camera view, which helps you line up with your desired track without looking at a flat screen. If the app you’re testing lacks AR or has a clunky calibration process, cross it off your list if you plan to use it in challenging conditions.

Step 5: Compare Subscription Tiers and Data Overhead

Most topo map apps for iPhone operate on a freemium or subscription model. Create a simple comparison table for the final two contenders you’re considering. Look at these metrics:

Don’t overlook the small print about data storage and tile expiration. Some apps delete cached tiles after 30 days unless you launch the app online; others keep them indefinitely. For a week‑long cruising trip without cellular coverage, tile expiration could leave you with blank screens. Also check whether the subscription includes weather overlays (rain radar, wind predictions) which are crucial for marine planning.

Step 6: Field Test the App Under Real Conditions

Before committing to a full year, use the free trial period (most apps offer 7–14 days) to test the app on an actual outing. Go to a known location where you have a paper chart or previous GPS track. Walk or sail a short route, record a track, drop waypoints, then use the AR mode to verify bearings. Ask yourself: How quickly does the GPS fix lock? Do the contour lines update smoothly as you pan? Can you switch between topo and satellite view without crashing? If the app feels sluggish or crashes when you have 10+ waypoints loaded, it will not serve you well on a busy day. For boaters, reliability under GPS lock and screen reflow is as important as map accuracy.

Step 7: Review Recent User Feedback and Developer Support

Finally, read the latest App Store reviews (sorted by “Most Recent”) specifically for the iPhone version. Look for comments about iOS 19 compatibility (since today is July 2026, the current iOS version matters). Pay attention to how responsive the developer is to bug reports in the forum or email. An app that hasn’t been updated in six months likely doesn’t support the new Core‑Location improvements or ARKit updates. Also check if the app offers community‑based chart corrections (like the NOAA chart updates portal) or a public backlog of known issues.

Bringing It Together: Your Decision Matrix

After completing these seven steps, you should have clear winners and losers. Rank your candidate apps on a scale of 1–5 for offline quality, AR usefulness, GPX handling, value, and iOS integration. For most recreational boaters and serious hikers, the best topographic map app for iPhone will be one that excels in at least three of these areas and has a developer actively maintaining it. If you frequently navigate coastal waters where depth, buoys, and hazard markers matter more than elevation contours, consider an app built specifically for marine contexts—like Sea Maps & AR—where the topo base map is augmented with NOAA ENC layers and AR waypoint beacons. Evaluate methodically, test in the field, and you’ll choose an app that becomes a trusted companion rather than a source of frustration.

Common Mistakes to Avoid When Selecting a Topographic Map App for iPhone

Even experienced boaters can make costly errors when choosing a topographic map app. The wrong app can mean lost waypoints, drained battery, or zero connectivity during a critical passage. Below are the most frequent missteps – and how to avoid them – so you can pick an app that truly performs on the water.

1. Prioritising Price Over Reliability

It’s tempting to download a free or cheap topo map app, but many such apps cut corners. Free versions often display outdated charts, lack offline tile caching, or include intrusive ads that pause or reroute your navigation. Others charge for essential features like GPX import or weather overlays, turning a “free” app into a costly subscription model. A reliable app like Sea Maps & AR: Boat GPS offers transparent pricing with all core features built-in – no hidden fees or forced upgrades.

2. Ignoring Offline Map Capability

One of the biggest mistakes is assuming you’ll always have cellular coverage. Coastal areas, offshore passages, and river inlets are notorious for weak signals. Without a full offline tile cache that stores high-resolution topo and bathymetric data directly on your iPhone, you risk being unable to see your position or planned route when the signal drops. Before committing to any app, test its offline download process: does it allow you to select and save large map areas? Does it preserve contour detail when disconnected? Apps that rely on streaming maps are useless in remote boating environments.

3. Underestimating Battery Drain

Running GPS, screen brightness at max, and continuous map rendering can drain an iPhone battery in under two hours. Many boaters choose an app without checking its power profile. The best apps use hardware-accelerated graphics and optimise refresh rates so they don’t burn through your battery. Look for apps that offer a low-power mode or “night mode” that dims the display. Also check if the app supports Apple Watch for quick glances, reducing the need to wake the phone repeatedly – a feature that Sea Maps & AR provides natively.

4. Assuming All Topo Apps Are Equal for Marine Use

Topographic maps designed for hiking don’t show critical marine data: water depth contours, submerged hazards, tide tables, or marine traffic. Conversely, pure nautical charting apps often ignore terrain above the waterline, which is essential for coastal approaches and anchoring in protected coves. The mistake is choosing a land-oriented app for boating or a chart-only app that lacks shoreline topography. A combined solution – like the hybrid topo/nautical maps used in Sea Maps & AR – gives you both land elevation and underwater contours in one seamless view. This is especially important when navigating narrow channels or entering unfamiliar harbors.

5. Overlooking AR Navigation for Situational Awareness

Augmented reality (AR) is not a gimmick; it’s a genuine safety tool that overlays waypoints, hazards, and chart lines onto the real-world view from your iPhone camera. Many boaters dismiss AR as novelty, but in low-visibility or cluttered anchorages, it can prevent collisions and help you spot buoys or shallows instantly. When evaluating an app, ask: does it use the iPhone’s compass, gyroscope, and GPS to render accurate AR beacons? Does it support landscape and portrait orientation? An app that integrates AR navigation – such as the AR waypoint beacon feature in Sea Maps & AR – gives you an extra layer of confidence when manoeuvring in tight spots.

6. Not Testing GPX Import/Export Before You Go

GPX is the universal file format for routes, tracks, and waypoints. A common mistake is assuming an app handles GPX correctly. Some apps import coordinates with a few meters of offset, or they don’t preserve altitude data from your previous track logs. Others export GPX files that are incomplete, missing time stamps or names. Before a long trip, create a test GPX route on your desktop app (or import one from a service like Navionics or Gaia GPS), then transfer it to your iPhone and verify each point on the chart. Only commit to an app that passes this test with 100% accuracy.

7. Forgetting About Software Update Frequency

Topographic data changes – new trails, altered shorelines, dredged channels, or updated hazard markers. An app that doesn’t push regular chart updates will become dangerously obsolete within months. Check the app’s changelog or support page: does the developer release updates at least quarterly? Do they respond to user-reported errors? For marine applications, the NOAA’s nautical chart updates are a good benchmark. An app that mirrors these updates shows commitment to accuracy. Sea Maps & AR, for example, refreshes its topographic and marine layers from authoritative sources, ensuring you never navigate with stale data.

8. Neglecting Apple Watch Integration

Your iPhone may be mounted at the helm, but during rough seas or when you need both hands free, a quick check on your wrist is invaluable. Many topo apps ignore the Apple Watch entirely, forcing you to grab the phone every time you need a bearing or waypoint direction. The mistake is not looking for an app that extends its core functions to the watch – like distance to next waypoint, heading, and alerts. This feature is not just a bonus; it can be a safety net when weather or waves make phone operation difficult.

Conclusion: Choose an App That Avoids These Pitfalls

The right topographic map app for your iPhone should be more than just a digital chart – it should be a reliable, always-ready navigation partner. By steering clear of the common mistakes listed above, you’ll save time, money, and potentially avoid a dangerous situation. Sea Maps & AR: Boat GPS was designed specifically to address each of these issues: it offers robust offline caching, low‑battery optimisation, true hybrid topo/nautical charts, AR waypoint beacons, GPX compatibility, frequent data updates, and full Apple Watch support. Whether you’re exploring coastal topography or planning a multi-day voyage, download Sea Maps & AR today and navigate with confidence.