An important part of a successful voyage is the ability to make modifications once the vessel is underway.
Because weather is typically the dominant, most variable, and least predictable factor when planning and executing a voyage, anything that can make the process run more smoothly and effectively should be utilized. Weather forecasts that you based your initial voyage plan on can change along the way. Sometimes the changes can be significant enough to warrant adjusting your voyage plan while en route, sometimes not.
If changes dictate that your initial voyage plan needs significant revision, a new plan is required (by both regulation and common sense). This might mean a simple reduction in speed to give bad weather ahead of you a chance to clear, increasing speed if possible to beat inclement weather into port, or altering your route to avoid or lessen exposure to the bad weather. This varies case-by-case and vessel-to-vessel for both the tug and the tow.
A method that has been very helpful to me, particularly on long-distance voyages, is the incorporation of weather waypoints into my normal navigation routes. By using the geographic boundaries that the National Weather Service uses to divide up its coastal, offshore and high seas forecast zones, you can easily and continuously keep track of where you are in relation to each zone in real time. It will provide you with good estimates of when you’ll cross into each zone and when you depart each zone.
For example, if you’re crossing the Gulf of Mexico from Tampa, Fla., to Corpus Christi, Texas, you’ll pass through the Northeast, North Central and Northwest Gulf offshore forecast zones. The north-south boundaries between them are at 87° and 94°W longitude, respectively, with the North Central zone sometimes subdivided at 90°W. Using your existing route, simply insert waypoints where those meridians cross your route’s track line and label them.
The method will work equally well when running coastwise, on larger inland bodies of water or in the Great Lakes.