The departure decision is the most consequential single decision the offshore passage produces. The decision to leave, to commit the boat and the crew and the twelve members aboard to the passage in the conditions the weather window offers, is the decision that the subsequent days of the passage live or die by.
The offshore captain who departs into a deteriorating weather window because the schedule required it, or because the marina berth was needed, or because the impatience of the people aboard overcame the judgment of the person responsible for the passage, has made the category of decision that the offshore sailing community discusses in the post-mortems of the incidents that those decisions eventually produce.
The departure decision on the Eighty2 begins four to five days before the planned departure date with the first look at the extended forecast. The GFS and the ECMWF models, the two primary global atmospheric models that the offshore sailing community uses for passage planning, are accessed through the passage planning software and the grib file viewer that translates the model data into the wind and pressure and wave height overlays that the navigator reads as the picture of the next ten days of atmosphere.
The models agree on some things and disagree on others, and the disagreement between them is itself information: the areas of the forecast where the two models diverge are the areas of the forecast where the atmosphere is least predictable and where the passage plan needs the most flexibility.
The Window and the Decision
The weather window for the offshore passage is the specific period in which the forecast conditions: wind direction, wind strength, wave height, the absence of the frontal system that would close the window before the passage is complete, are suitable for the passage in question. Not perfect: the offshore sailing life does not produce perfect weather windows. Suitable.
The window that gives the passage a reasonable chance of completing in conditions that the boat and the crew and the members can manage without the passage becoming the situation that requires the management of an emergency rather than the management of a sailing trip.
Twenty-four hours before the planned departure Sven calls the professional weather routing service that the Naora programme uses for the major passages, the Atlantic crossing, the Pacific legs, the Indian Ocean crossing. The weather router has access to the same model data I have and the specific professional expertise of the person who does this full-time for offshore vessels on these routes. It’s also a good friend of Sven, we will introduce him later in our blog section.
The conversation is fifteen minutes: the current model picture, the specific concerns for this passage at this time of year in this region, the window assessment, and the specific recommendation about the departure timing. The final decision is for Sven. The weather router’s input is the professional validation of the assessment Sven have already made independently, or the flag that the assessment needs revision.
The departure happens when the window opens. Not when the schedule says. Not when the marina berth expires. When the window opens. This is the non-negotiable principle of the offshore passage planning on the Naora voyage. The members are briefed on this from the first conversation. The schedule is the best estimate of when the window will open. The window is what determines when the boat leaves.
