Weather Routing Quiz

Wind speed limits create exclusion zones. The algorithm treats areas above the threshold as impassable and finds a path around them, even if the detour adds distance and time.

Each tack costs time (boat deceleration, crew work, rebuilding speed) that the pure algorithm ignores. Penalties make the router weigh these costs, typically producing routes with fewer tacks and longer, more comfortable sailing legs.

Motor speed provides a fallback velocity for calm conditions. When the polar says the boat would sail too slowly, the router uses motor speed instead — allowing it to transit calms directly rather than making long detours.

Theoretical polars assume racing conditions. Real-world factors — bottom growth, aging sails, conservative handling, sea state — mean most cruising boats achieve 85-95% of their published polars. Setting the efficiency correctly produces realistic ETAs.

Wind speed limits prevent the router from sending you through gale-force conditions when a reasonable detour exists. For cruisers, this single parameter has the greatest impact on route quality and safety.

Shorthanded crews face significant effort per tack — disengaging the autopilot, winching, managing sails, rebuilding speed. A generous penalty (15-20 minutes) produces routes with long, stable legs that are practical for two-person crews.

Published polars represent theoretical maximum performance. Real boats with growth, aging sails, and practical (non-racing) sail handling typically achieve 85-95% of their polars. Setting this correctly produces accurate ETAs.

When wind drops below the minimum sailing threshold, the router uses motor speed as a fallback. This often produces shorter, more practical routes that transit calm zones directly rather than sailing long detours to avoid them.

GRIB wind scaling adjusts all forecast wind speeds by a percentage to compensate for known model bias. It should be used cautiously — in most cases, adjusting polar efficiency is a better approach than second-guessing the forecast model.

The radial axis of a polar diagram represents boat speed. The further a curve extends from the center at a given angle, the faster the boat is sailing at that TWA.

Beam reach (approximately 90° TWA) is almost always the fastest point of sail on a displacement sailboat. The polar curves typically extend furthest from center near this angle.

Polar files for weather routing software use semicolons as separators, not commas. This is true for both .pol and .csv formats, which is a common source of confusion.

The ORC (Offshore Racing Congress) uses Velocity Prediction Programs to generate polars for their rating system. These polars are based on precise hull measurements and are among the most reliable available.

Theoretical polars are generated by VPPs that assume perfect conditions — flat water, clean hull, optimal sail trim, and full crew. In the real world, sail age, bottom growth, sea state, and crew limitations all reduce performance below theoretical values.

Each point on a polar curve sits at a specific true wind angle (the angular position) and boat speed (the radial distance from center). The curve itself corresponds to a single true wind speed value.

The header shows TWS values: 6, 8, 10, 12, 16, 20. The 12-knot column is the fourth data column. At 90° TWA, the fourth value is 6.9 knots.

Polars are symmetrical — performance is identical on port and starboard tack. Bottom growth, sail age, and sea state are all real-world factors that cause actual performance to fall below theoretical polar values.

Polars are available from multiple sources: manufacturers often publish them, the ORC database contains VPP-generated polars for rated boats, and virtual sailing platforms create calibrated polars for hundreds of boat types.

Most cruising boats perform at 75-90% of their theoretical polar. Losses come from sail age, bottom condition, sea state, and crew efficiency. Using 100% will consistently overestimate performance and produce unrealistically fast ETAs.

The base map provides excellent geographic context for weather routing, which operates at scales of tens to hundreds of miles. Detailed navigational charts are only needed when using qtVlm as a chartplotter for near-shore navigation.

BSB/KAP is the standard raster chart format — essentially a high-quality scan of a paper chart with geographic coordinates embedded. NOAA distributes free BSB/KAP charts covering all US waters.

Vector charts store data as objects rather than fixed images, so they scale without pixelation and allow you to click on features to see their properties. This makes them more versatile for navigation at varying scales.

Online chart tiles are fetched from internet tile servers in real time. Offshore without internet, they're unavailable. This is why downloaded chart files (BSB, S57, MBTiles) are essential for offshore use.

NOAA distributes free raster navigational charts in BSB/KAP format, covering all US waters. These are georeferenced images of traditional paper charts.

The base map covers the globe with coastlines and geographic context — adequate for weather routing, which operates at scales of tens to hundreds of miles. No additional charts are needed for pure routing work.

Vector charts store chart features as individual objects (buoys, depth contours, land areas) rather than fixed images. This means clean scaling at any zoom level and the ability to click on objects to see their properties.

MBTiles package chart tiles into a single SQLite database file — compact, fast, and fully offline. This makes them ideal for offshore use where internet-dependent online tiles aren't available.

Charts → Manage Charts is the central configuration for all chart sources. You set directories, loading priorities, and zoom-level preferences. qtVlm then automatically loads the best available chart as you pan and zoom.

Virtual ocean racing demands the same routing calculations as real offshore sailing. Thousands of competitive virtual racers stress-tested qtVlm's routing engine, exposing and fixing bugs and performance issues — producing a reliable tool for real-world use.

qtVlm ships with minimal base maps to keep the installer small. After first launch, you download higher-resolution charts and configure the display settings. This is a normal part of the initial setup process.

GRIB file operations — opening, downloading, and managing weather data — are accessed through the Grib menu. qtVlm supports multiple GRIB slots so you can load different data sets (e.g., wind in Slot 1, wave data in Slot 2).

The night zones overlay shades areas that are in darkness at the current forecast time. This helps with passage planning — particularly for timing arrivals at unfamiliar ports during daylight and understanding day/night thermal effects on coastal wind patterns.

qtVlm's desktop version is completely free with no restrictions. The developer relies on voluntary donations from users and revenue from the paid iOS/Android versions (~$10). This donation model works because a large, engaged virtual racing community supports the project.

qtVlm runs on Windows, Mac, and Linux as a free desktop application. Paid versions (~$10 one-time purchase) are available for iOS and Android through their respective app stores.

All GRIB-related operations — opening files, downloading data, and managing weather data — are accessed through the Grib menu. Multiple GRIB slots allow you to load different data sets simultaneously.

qtVlm ships with minimal base maps to keep the installer download size manageable. After installation, you download higher-resolution charts through the program's map download feature.

The night zones overlay shades areas that are in darkness at the current GRIB time step. It's useful for planning daylight arrivals and understanding thermal wind effects related to the day/night cycle.

qtVlm became the dominant tool in virtual ocean racing, where thousands of competitive users ran intensive routing calculations with real GRIB data. This extensive stress-testing exposed and fixed bugs, producing a battle-tested routing engine.

GRIB stands for GRIdded Binary. It is a standardized file format developed by the World Meteorological Organization for efficiently storing and transmitting gridded weather forecast data.

GFS is free, global, and good enough for most routing. ECMWF is more accurate, particularly in medium-range forecasts, but access to full-resolution data requires a paid subscription.

In the open ocean, wind patterns are large-scale — there are no coastal effects, channels, or islands that require fine resolution. The 0.5° grid captures everything the routing algorithm needs at half the file size.

Wind at 10 meters is the fundamental input. The routing algorithm combines wind speed and direction at every grid point with your polar diagram to calculate boat speed and optimal heading. All other parameters are supplementary.

GRIB files contain forecast data — predictions from numerical weather models — arranged on a regular grid with data at multiple future time steps. They are not observations, imagery, or historical data.

GFS is free (no subscription needed), covers the globe at 0.25° or 0.5° resolution, and runs four times daily. While ECMWF is generally more accurate, GFS provides sufficient quality for most recreational routing without any cost.

File size is controlled by three factors: area, resolution, and parameters. Limiting all three — a small area around your route, lower resolution for open ocean, and only essential parameters — can reduce a 15 MB file to under 100 KB.

Wind at 10 meters is the fundamental input — the routing algorithm combines wind data with your polar diagram to calculate boat speed. Without wind data, routing is impossible. Other parameters are supplementary.

Regional models run at much higher resolution (as fine as 3 km versus GFS's 28 km) over limited areas. This captures local effects — thermal breezes, wind funneling, coastal convergence — that global models smooth over.

Checking the forecast provides weather information. Weather routing goes further by combining that forecast with your boat's polar diagram to calculate the optimal route — it converts weather data into an actionable sailing plan.

Weather routing requires a wind forecast to know what the wind will do and a polar diagram to know how the boat performs in those conditions. Without either input, the routing algorithm cannot calculate an optimal route.

Maury analyzed thousands of ship logbooks to map average wind and current patterns by season and location. His published charts recommended routes that dramatically reduced passage times — the New York to San Francisco route dropped from 183 to 133 days average.

Weather routing provides the most value when the wind field varies significantly across the sailing area and over the passage duration. Ocean crossings involve multiple weather systems over 2-3 weeks — routing can find paths that exploit favorable winds and avoid storms, saving days and improving safety.

Checking the forecast tells you what the weather will be. Weather routing goes further by combining that forecast with your boat's performance characteristics to determine which route to take — it's the difference between knowing the weather and knowing what to do about it.

The routing algorithm needs to know what the wind will do (the GRIB forecast) and how the boat performs in various wind conditions (the polar diagram). Without both inputs, it cannot calculate an optimal route.

Maury analyzed thousands of ship logbooks to map seasonal wind and current patterns, then published recommended routes. The New York to San Francisco passage around Cape Horn dropped from an average of 183 days to 133 days — a 27% improvement through better routing alone.

The optimal route considers how the wind field evolves over time. Sailing extra miles to catch a favorable wind shift or avoid a headwind zone can result in a faster passage than the straight-line route, because the boat spends more time sailing efficiently.

Weather routing adds little value on short passages in uniform conditions. A 10-mile day sail in steady winds has no routing puzzle — the wind won't change significantly during the passage. The other scenarios all involve enough time and distance for weather patterns to shift meaningfully.

The boat configuration is accessed through Boat > Boat Settings in the main menu bar. The Polars tab within this dialog is where you import your polar file.

qtVlm accepts .pol and .csv files for polars, but both must use semicolons as the value separator. Despite the .csv extension suggesting commas, the weather routing convention is semicolons.

The Wind Polar analysis view is accessed through Boat > Polars > Wind polar. This displays your imported polar data as a graphical plot for visual verification.

Aging sails cost 10-15%, bottom growth costs 5-10%, and double-handed sailing costs 10-20%. Combined, these factors put realistic performance around 70-80% of the theoretical polar for typical cruising conditions.

Multiple profiles allow you to route with different polars and efficiency percentages matching your actual sailing configuration. A boat under full racing canvas performs very differently from the same boat with reefed cruising sails.

The boat configuration — including the Polars tab for importing polar files — is accessed through Boat > Boat Settings in the main menu bar.

The most common cause of failed or garbled polar imports is incorrect separators. Both .pol and .csv polar files must use semicolons, not commas. Despite the .csv extension suggesting comma separation, the weather routing convention is semicolons.

A correctly imported polar shows smooth, nested curves — each higher TWS curve sits at or outside the previous one. Curves that cross, have flat spots, or show sudden jumps indicate data errors.

Five-year-old sails cost roughly 10-15%. Eight months of bottom growth costs at least 5-10%. Double-handed sailing costs 10-20%. Combined: roughly 25-45% total deduction, putting realistic efficiency at 65-75%.

Running multiple profiles gives you a realistic window of arrival times. If both optimistic and conservative profiles show you making your destination before the weather changes, you have a solid weather window. If only the optimistic one works, waiting is the safer call.

Multi-routing runs the full routing algorithm repeatedly, each time with a different departure date/time. This produces a family of optimal routes that you can compare to find the best departure window for your passage.

Multi-routing requires an earliest departure date/time, a latest departure date/time, and the interval between successive routing computations. These three parameters define how many departure scenarios the algorithm will evaluate.

When routes diverge significantly between departure times, it means the weather pattern is evolving rapidly. Small changes in departure timing put the boat in very different conditions, causing the algorithm to find fundamentally different optimal paths. This is precisely when multi-routing is most valuable.

The most practical approach is to filter departures by your crew's comfort and safety limits first, then choose the fastest passage among the remaining options. This combines the algorithm's optimization with human judgment about real-world constraints.

Modern global models (GFS, ECMWF) are reliable to about 3 days, useful to 5 days, and increasingly speculative beyond 7 days. Multi-routing results for departures more than a week out should be treated as general trend indicators, not detailed predictions.

Multi-routing computes the optimal route for each departure time within a specified window, allowing you to compare passage duration, conditions, and route shape to identify the best departure.

In rapidly evolving conditions, a 3-6 hour interval captures weather windows that open and close quickly. A 12 or 24-hour interval might miss critical departure opportunities around the frontal passage.

This is a classic departure cliff — a sharp transition where a passing weather system (front, shifting high, etc.) fundamentally changes the conditions. Tuesday departures get ahead of the system; Wednesday departures must route around it.

Global weather models lose detailed accuracy beyond 5-7 days. Routes computed on speculative forecast data may look promising but reflect smoothed-out conditions that will differ from reality as the date approaches.

The iterative approach maximizes the value of improving forecast accuracy. Broad early runs identify the best general timeframe; subsequent runs with fresh data and narrower windows pinpoint the optimal departure with increasing confidence.

Coastal passages have limited route options (constrained by coastline, channels, hazards). The real value of routing is evaluating multiple departure times to find the weather window that produces the most comfortable, manageable passage.

Weather routing considers wind at every point along the route. A path that's 200 miles longer but runs through 15-knot reaching conditions is much faster than a direct path through a calm zone or headwinds. Distance is secondary to boat speed.

Small forecast variations between updates rarely justify course changes. Responding to every minor shift produces an inefficient zigzag path. Reserve course changes for significant weather developments — new systems, major front timing changes, or high-pressure shifts.

NMEA input displays your live boat data on the same chart as your weather route. You can monitor progress against the plan, compare actual conditions to the forecast, and re-route from current position — combining planning and navigation in one display.

Coastal passages have limited route options due to geographic constraints. The primary value is evaluating departure times to find the weather window that best matches your conditions preferences.

Weather routing optimizes for time, not distance. A route that's 200 miles longer but through reaching conditions is faster than the direct path if the rhumb line crosses calm zones or headwinds.

For a 5-day crossing, daily or every 36 hours is optimal. This catches significant forecast changes while avoiding the trap of constant small course corrections that produce an inefficient zigzag.

NMEA connects your instruments to qtVlm, showing real-time data alongside the weather route. This lets you monitor progress against the plan, compare actual conditions to the forecast, and see AIS traffic in context.

Multi-routing evaluates different departure times for the same passage. By comparing duration, maximum wind, and comfort metrics across departures, you identify the weather window that produces the best passage.

Each Pathway waypoint forces the router through an exact position. Too many waypoints leave no room for the algorithm to optimize — you're essentially drawing the route manually instead of letting the weather routing calculation do its job.

Boundaries are hard obstacles for the routing algorithm. Isochrones cannot expand through them, and the router must find paths around them. They function exactly like coastline in the algorithm's calculations.

A Gateway is a line segment the route must cross, giving the router freedom to choose the optimal crossing point. A Pathway waypoint forces the route through one exact position. Gateways are more flexible and often produce better routes at channel entrances and strait crossings.

Iterative refinement produces the best results. Start simple, examine the output, and add constraints one at a time to address specific problems. Each constraint reduces the router's optimization freedom, so only add what's genuinely necessary.

Gateways let the router choose the optimal crossing point along a line. Use them when you need the route to pass through an area (a strait, a channel) but the exact position within that area should be weather-optimized.

Boundaries should include safety margin beyond the actual hazard. Exact placement on a depth contour provides zero margin for GPS accuracy, chart datum differences, and the routing algorithm's grid resolution.

Each Pathway waypoint removes routing freedom. Too many waypoints turn weather routing into manual route drawing — you're telling the router exactly where to go, eliminating its ability to find better paths through the forecast.

Iterative refinement preserves maximum optimization freedom while addressing specific hazards. Each added constraint should demonstrably improve the route — if it doesn't, remove it.

Saved Boundaries capture permanent or semi-permanent hazards (shoals, TSSs, restricted areas) for frequently sailed routes. On repeat passages, the constraints are pre-configured — you only need fresh weather data.

TWA (True Wind Angle) shows the angle between the wind and your course — your point of sail. A TWA of 45° is a close beat, 90° is a beam reach, 135° is a broad reach, and 180° is a dead run. This tells you what kind of sailing each leg will involve.

Statistics provide headline comparisons across routes. Running the same route for multiple departure times and comparing stats reveals which weather window produces the shortest, safest, most comfortable passage.

GPX files contain geographic data only — waypoint positions, names, and the route sequence. Weather data, timing, and routing parameters are not included. The chartplotter treats the imported route as a conventional set of waypoints to navigate.

A printed plan provides redundancy if electronics fail, works as a crew briefing document everyone can study, and serves as a quick reference without navigating menus on a bouncing boat. It's good seamanship to have a paper backup.

The logbook reveals the actual sailing experience the route proposes — conditions at each time step. Pay particular attention to nighttime entries and any periods of strong wind, uncomfortable points of sail, or difficult maneuvers.

The histogram's visual format makes patterns immediately obvious — wind spikes, calm zones, transitions between points of sail — that might not stand out in a table of numbers.

Chartplotters are easier to use with fewer waypoints. A simplified route captures the essential course changes in a manageable form. Keep the detailed version in qtVlm as a reference for the full routing intent.

A complete route plan serves as both a crew briefing document and an electronics-failure backup. It should contain enough information to navigate the passage and make pre-planned decisions about diversions.

Total duration matters, but maximum conditions determine safety and comfort. A route that's slightly longer but keeps wind under 20 knots is often preferable to a faster route through 30-knot conditions — especially for cruising crews.

Current data adds a velocity vector at every grid point. The router calculates true speed over ground — boat speed through water plus or minus current — and optimizes the route accordingly. This can significantly change optimal routes near major current systems.

Polar diagrams assume flat water. Real waves slow the boat through hull motion, spray, and difficulty maintaining optimal sail trim. Reducing polar efficiency by 10-15% for rough conditions produces more realistic routes and ETAs.

Crew fatigue is real and cumulative. By Day 3-5, sail handling slows, reaction times increase, and conservative decisions (not pushing sail area) reduce performance. Building this into your routing parameters produces more honest ETAs.

Consistently late arrivals indicate the router overestimates your boat speed. Reducing polar efficiency by 10-15% tells the router to assume lower performance, producing more accurate ETAs and sometimes different (better) routes.

RTOFS (Real-Time Ocean Forecast System) provides current forecasts as GRIB data. For Gulf Stream crossings, current data can change the optimal crossing point by 50+ miles and save a full day on the passage.

Polar diagrams represent flat-water performance. Real waves slow the boat through hull motion, spray, and trim difficulty. Without accounting for this, routes and ETAs are optimistic — sometimes significantly so in rough conditions.

Nighttime landfall with a fatigued crew is one of the most dangerous situations in sailing. If the router produces an ETA during darkness, consider shifting departure time to achieve daylight arrival.

Individual passages are affected by forecast accuracy, unusual conditions, and random factors. Trends across 3-5 passages reveal whether your settings systematically over- or under-predict performance, providing a reliable basis for adjustment.

Speed over ground = speed through water ± current. In areas with strong currents (Gulf Stream at 3-4 knots, tidal straits at 2-3 knots), the difference is enormous and dominates routing decisions.

An isochrone connects all the positions a boat could reach in the same amount of elapsed time from the start point. It is a contour of equal travel time, not distance or wind speed.

The algorithm is recursive. Each new time step begins from the full extent of the most recent isochrone, not from the original start point. Every point on the previous isochrone becomes a new origin for trial headings, allowing the algorithm to explore all possible paths through the shifting wind field.

Wide isochrone spacing means the boat covers more ground per time step — favorable wind angle and/or stronger breeze. Tight bunching means slow going. The algorithm will route the boat toward the widely spaced direction to minimize total passage time.

The algorithm optimizes total arrival time, not instantaneous speed. Sailing through a temporarily slow area can position the boat to exploit a coming wind shift or stronger breeze, making the overall passage faster than avoiding the slow zone entirely.

An isochrone is defined by equal elapsed time from the start position. Points on the same isochrone may be at very different distances from the start — because the boat travels faster in some directions than others — but they all represent the same amount of sailing time.

At each time step, the algorithm uses the boat's polar diagram (boat speed vs. wind angle and speed) and the GRIB forecast (wind speed and direction at each position and time) to calculate how far the boat could travel on each trial heading.

Wide spacing between isochrones means the boat covers more ground per time step — favorable wind. Tight spacing means slow progress due to headwinds, light air, or adverse current. The contrast between directions directly maps to the wind pattern.

When the time step is smaller than the GRIB resolution, the algorithm interpolates wind values between GRIB snapshots. This adds significant computation time but the interpolated data is estimated, not observed, so the accuracy gain is limited.

The algorithm optimizes total arrival time, not speed at every moment. Sailing through a slow patch can be worthwhile if it positions the boat to catch favorable wind later — the temporary slowdown is more than compensated by faster sailing afterward.

Right-clicking on the chart brings up the context menu where Create POI is the primary option. The right-click position pre-fills the coordinates, and you can name the point and add notes in the dialog.

The routing algorithm adjusts course at every time step (often every 30 minutes), producing a path with hundreds of small heading changes. This is mathematically optimal but impossible to hand-steer. Converting to a Route simplifies it into practical sailing legs.

Simplify reduces a route from potentially hundreds of waypoints to a manageable number (6-12 for a typical passage) while keeping the simplified path within an acceptable distance of the theoretically optimal Routing. This makes the route practical to navigate.

Pathways add mandatory intermediate waypoints that the router must pass through. Use them when real-world constraints (channels, headlands, shipping lanes, intermediate stops) require the route to follow a specific sequence of points.

A Routing is the theoretically optimal path with course changes at every algorithm time step. A Route is a simplified version with practical waypoints — the result of converting, simplifying, and optimizing the Routing.

Right-clicking on the chart opens the context menu where Create POI is the primary option. The clicked position pre-fills the coordinates in the dialog.

Simplification alters the route geometry. Without re-optimizing, the timing, leg durations, and expected conditions still reflect the old path. Optimize recalculates everything along the new, simplified route.

Pathways force the routing algorithm through mandatory intermediate points — essential for coastal routes where real-world constraints (narrow channels, headlands, shipping lanes) must be respected.

GPX (GPS Exchange Format) is the standard for exchanging navigation data between software and devices. qtVlm can import POIs from GPX files and export them for use in chartplotters or other navigation software.

Ctrl+G opens the GRIB file dialog in qtVlm. You can also use the menu path Grib → Open Grib. For downloading a new GRIB directly, use Grib → Download Grib instead.

Right-clicking on the chart shows a tooltip with the exact forecast values at that grid point for the current time step. This is essential for checking conditions at specific locations along your planned route.

Color fill represents wind speed using a color gradient. It's the best display mode for quickly understanding the overall wind pattern — where it's strong, where it's calm, and where gradients are steepest.

Two GRIB slots let you layer a detailed regional model over a global model, or compare two different forecast models. Where models agree, confidence is higher. Where they disagree, you know to plan conservatively.

Grib → Download Grib opens the download dialog where you configure the area, model (GFS default), resolution, forecast duration, and which parameters to include. The file is fetched from NOAA's servers.

The left and right arrow keys step backward and forward through GRIB time steps. You can also click directly on the time bar at the bottom of the screen to jump to a specific time.

Wind barbs show the direction the wind is coming FROM, following standard meteorological convention. A barb pointing from the northwest represents a northwest wind that blows toward the southeast.

Understanding the weather pattern — where systems are moving, when fronts pass, where wind windows open — lets you evaluate the routing algorithm's output with informed judgment. A route that looks optimal might take you too close to a developing low.

Two slots let you layer a detailed regional model (NAM, ICON) over a global model (GFS) — giving you high-resolution coastal effects near shore and broad coverage for the open ocean portion of your passage.

'Routing from boat' forces the start position to your boat's live GPS coordinates. When planning ahead from a computer — often from a completely different location — you need the routing to start from the POI you placed on the chart, not from where the boat (or computer) currently sits.

The routing algorithm evaluates boat progress at every isochrone time step (e.g., every 1–3 hours). Each step produces a waypoint where the algorithm determined the optimal heading. The result is a highly detailed but impractically dense set of course changes.

Maximum simplification aggressively removes waypoints, producing the fewest possible course changes. The trade-off is that the route deviates further from the algorithm's optimal path, which can add meaningful time — especially when wind shifts are sharp and frequent.

Unlike the initial computation which solves the entire passage at once, optimization takes the simplified waypoint positions as fixed constraints and re-routes between each consecutive pair. This lets it fine-tune departure timing and heading for each leg individually, often recovering time lost during simplification.

When isochrones stop partway, it almost always means the GRIB data ran out — either geographically (the forecast area does not extend to the destination) or temporally (the forecast ends before the boat could arrive). Download a GRIB with broader coverage and a longer time span.

The workflow is: Create a Routing (compute isochrones), Convert to Route (turn the result into a navigable route), Simplify (reduce waypoints), and Optimize (refine leg-by-leg timing). Each stage builds on the previous one.

For advance planning, disable 'Routing from boat' so the start position uses your placed POI, and enable 'Keep Starting Date' so qtVlm does not reset your departure time to now every time you recompute.

A 12-hour increase suggests Maximum simplification removed too many waypoints and the route cannot track the wind shifts. Optimum simplification retains more waypoints where heading changes matter, typically recovering most of that lost time.

Optimization takes the fixed waypoint positions from the simplified route and re-runs the routing algorithm between each consecutive pair. This leg-by-leg approach lets it refine departure timing and heading at each waypoint, often recovering time lost during simplification.

Setting the slider to Best accuracy increases computation time but does not prevent a routing from working. No GRIB, no polar, and a start time outside the GRIB range are all common causes of failed routings.