I would propose that (?) there is no way any software
can give you anything like even marginally reliable routing beyond X days' horizon(?). Not even in a boat as big and fast as a Lagoon
500, I believe. We can attempt to establish what the above X is.
However, the exercise you want is easy to do with any wx routing package, you can do the following, e.g.:
DAY ONE: set the points and pick up the polar, DERATE according to how the boat is sailed/loaded/equipped, DERATE according to the sea-state, download the grib, run the model, check if you agree, if you do: MARK DAY ONE END POINT.
DAY TWO: use the marked above waypoint as your boat position, repeat the whole exercise (download fresh gribs, etc).
Do the above, say daily, and you get to see a what it would be like in real life. It takes about two or three weeks of daily (or any other period) attention.
The above routine will work
as if you have sailed an actual passage
. But it must be done on a regular daily or other periodical basis - for you can download the gribs daily and run the exercise at a future point - only if you are very keen on manipulating the routing software
. And not all software allows you to manipulate this much either.
On reading the weatherfax chartlets: It is indeed a very very easy thing. The air around the Low and High cells moves in its distinct manner - direction and speed related to center, etc. The other visible features are fronts and on a front there is a specific set of wx features too - typical cloud formations, wind shifts, sea state conditions. So this is like a general plan telling you the train is coming and what kind of train it is. The grib data interpreted by any software will tell you then how fast the train is moving and also at what angle it will hit you.
It takes not more than a week of intensive study to be quite literate with interpreting a weather fax image. And it is best done while you are there - so that you can see the features shown in the wxfax as they pass around you - the change in air clarity, the change in cloud formations, the wind shifts, the lightening and the wind turn on the ridge and the acceleration and the wind shift on the front. Etc.
Wxfax images are a great tool to predict the best days to watch out for a green flash when you are in the Caribbean
- for you want to know when the pre-front clearing comes. A grib file will not tell you this. But looking at the horizon every morning will. The beauty of using various sources and seeing what they actually attempt, and can/cannot, describe.
Can you possibly let me know what passage
time your software generated for your boat? I am surprised you got full passage covered
as my longest gribs show 10 days data and beyond 4 days I no longer use this data for any planning. But even with the max 10 days' grib data, vastly unreliable as it is, I do not think my packages (MaxSea and qtVlm) could predict a Lagoon 500 getting from the West Indies to the Azores.
Choice of departure time and timing is dependent on how strong the boat and crew are: North Atlantic speed records are often attempted at times when no cruising boat should leave the harbour. The rest is choices of the skippers who are ultimately responsible for safety
of their crews.