By Captain Lisa Batchelor Frailey, Kinetic Sailing
Savvy navigators know that planning a passage includes a careful blend of seamanship, navigation, meteorology, and oceanography. Even if the trip is one you make every season, the solution will differ because some variables will change. I developed this 10-step methodology to ensure that all the bases are covered, and I use it when teaching marine weather and passage planning to students, and when planning my own voyages. It breaks the process into discrete, manageable chunks and is scalable for short hops or long voyages. Following these steps will allow you to optimize all the factors involved for a safe, efficient passage.
- Know your boat – performance and constraints. This includes performance under both sail and power. Sailing polars are part of the picture, but ensure they are scaled for a cruise-laden boat with a non-racing crew. When inshore, will your boat’s mast height or draft be a factor? Assess your boat’s cruising speed, available fuel, and range under power. Consider your available fresh water, including tankage and watermaking capacity. Does your crew have constraints, whether timing or physical? Do you have the communications gear to support your navigation plan? Evaluate your distance offshore against the range of VHF, cellular, or satellite communications.
- Climatology. Studying long-term patterns for weather and currents over a geographic area is often the most overlooked step in the passage-planning process. There are numerous resources, including pilot charts (paper and digital), cruising guides, the National Hurricane Center, and NOAA’s 6-month Climate Forecast System (CFS) model. Studying climatology helps you select the right ocean for the right season and provides insight into what to expect and prepare for. Some sources provide route guidance based purely on climatology – that’s a great starting point for long-range planning.
- Navigation plan. Whether you prefer paper or electronic, you need to use reliable, accurate charts of an appropriate scale. I like to have a planning chart that depicts the entire route, and to supplement it with large-scale (small-area) charts for the departure, destination, and en route portions that require high-resolution data. You can find the correct scales in chartbooks or in electronic apps like Aqua Map. If you primarily use a chartplotter underway, be sure to have backup charts on a smartphone or tablet. Plot the shortest navigable route to your destination, considering your draft and air draft. Use meaningful, transferable waypoints, especially if you’re working between paper and electronic charts. Modify your route based on climatology (e.g., do you need to get east before turning south, anticipating trade winds?). Using a realistic cruising speed (remember step 1) and the distance on your navigable route, calculate the estimated time en route. Plot your anticipated daily progress on your chart – this will help focus your weather analysis.
- Pre-fly and Modify. Many Aids to Navigation (ATONs) or hazards only show up when the chart is zoomed in. Zoom in (electronically or use higher-resolution paper charts) to “pre-fly” your route from start to finish, ensuring it’s clear of hazards and obstacles. Modify your waypoints accordingly. This pre-flight is especially important if you use an auto-routing feature.
- Identify Alternates. Weather, fuel, maintenance, or injury may require you to add a stop or alter your destination. Identify and annotate suitable alternates on your chart, and be sure you have appropriate charts to allow safe access. On electronic charts, place a marker at the entrance to your alternates so you can find them easily at any scale.
- Apply Tides & Currents. Now that you have a navigable plan, reviewing the tides and currents will help you assess the timing, or know what to expect if timing is not so flexible. Tides and tidal currents are predicted two years in advance and are available online and in many navigation apps, including Aqua Map. Ocean currents are less predictable, but persistent currents are indicated on most navigation charts. Forecast models are run several times per week, with data available in graphic and GRIB formats within apps. A strong ocean current, like the Gulf Stream, will influence your route, speed, course, and timing.
- Analyze and Apply Marine Weather. Now we gather and analyze the forecasted weather for our planned passage. First, study weather maps to get the big picture. What synoptic features are in play? How frequently do Lows or fronts pass? Where do the trade winds set in? I prefer to use synoptic forecast maps, but forecast models provided in GRIB format via apps are great tools, especially when compared with maps. Ensure you are using the correct scale forecast model; a global model may suffice for ocean passages, but a mesoscale or high-resolution model is needed for inland and coastal trips. High-resolution models are typically valid for 1-2 days, whereas global models may extend to 16 days. However, the reliability of any forecast decreases significantly after 2-3 days. Now you can drill down into various graphic and text forecasts for the specific segments of your passage. Start with forecasts provided by your national marine forecast authority, who have regional expertise. If you’ve marked off your approximate daily position on your chart, this task will be simplified, as text forecasts are provided for specific geographical blocks. Use a planning worksheet to note synoptic features, wind speed/direction/gusts, seas and swell, and hazardous precipitation. Take note of wind “influencers” like thermal heating (sea breeze) and terrain that might create gap or katabatic winds. Many weather apps allow you to select and display forecast parameters of interest, so you can toggle through them to get a more refined picture. Note consensus or discrepancies between model guidance and professional forecasts. Analyzing the weather forecasts is crucial to your selection of a weather window – a period of weather suitable for your intended passage. Knowing your boat and your thresholds helps to define what’s acceptable (vs optimal). You may be able to complete your passage in 2-4 days, but for longer passages, you’ll need to be prepared for whatever you find in the long-range forecast, and update frequently to reshape your course for safety, speed, and comfort.
- En route - Shape and Reshape the Course. Having selected your weather window for departure, you may need to reshape the course for the first few days of your passage. Shaping is important to take advantage of sailable winds, avoid big or confused seas, and use beneficial currents. Once underway, keep a log of your weather observations, including wind, sea state, pressure, sky condition, precipitation, and sea surface temperatures. Note the trends, and compare your observations with analyses and forecasts for coincident times. Use your onboard radar to spot and avoid weather cells. Download updated weather frequently – at least twice a day on longer passages, and more frequently if conditions are rapidly changing. If you’re employing a weather routing service, provide them with feedback and observations so they can better refine your routing guidance. Reshape your course as your forecast refines. You may need to alter course or speed to avoid hazards or to meet favorable wind; this may involve motoring to meet the wind, or to cross a trough or ridge.
- Make a Pilotage Plan for your Destination. As you approach your destination, study the high-resolution approach and guides. In addition to plotting your arrival plan on your charts, sketch it out on paper – this helps engrave the plan in your brain. Use reliable visual references, create turn bearings, and annotate hazards to watch for. You may need to adjust your speed and timing to arrive in daylight with good visibility. Brief the crew on their positions and tasks for the arrival.
- Post-Passage Review. Now that you’ve safely arrived at your destination, close out your float plan, celebrate your success, toast the crew, and have a rest. Before the passage becomes a distant memory, do a review – compare your log and track against the analyses, forecasts and routing guidance. Were the products sufficient and accurate? Did you make good decisions on course shaping, or is there room to improve? Would you modify your wind and seas thresholds? Take notes so you can apply the lessons learned to your next passage.
Every boat, crew, and passage is different, but applying this scalable methodology will help you evaluate all relevant environmental parameters and make better decisions about safer, more efficient passage routing.
Note -- To learn more and practice, see: Marine Weather Course & Voyage Planning Practical
