Wayplanner Alternative

[prv]

And you dont need software to determine that event

Indeed I don't, see my very first reply to this thread.

In fact, please re-read the thread in general, and stop imagining what you think people might have said.

going "on the tide" is the only way unless one is a numpty or like`s to travel the scenic route

Yes, you keep making that point. I can't imagine why, when the whole point of this thread is to agree with it.

Pete

 

[rob2]

OK, so it was slightly more complicated than I could be bothered to write originally! The straight line was indeed drawn between start and finish and a time calculated when we should drift back across this. It was any offset at that moment that was used to calculate actual tidal strength for subsequent calcs. As boat speed is parallel to the straight line the ratio of progress can be used to estimate ETA. It gets more complex as you close the coast, especially as the vector may well not follow the straight up and down nature of the greater part of a channel crossing. For manual chart work it was effective to establish suitable points where the significance of a position check would not be ambiguous. If mechanical computation is used then these corrections can be more or less continuous, which is the ideal way to sail the most efficient course, separating the possible variations in the errors, such as log reading (speed through water) and tidal vector will improve if the algorithm incorporates a suitable feedback mechanism.

Rob.

P.S. Whoops, a bit of a Doctor Who moment! Forgot to mention that another rogue variable is time... if the tide is actually happening late or early, everything changes.

 

[Robin]

+1. Although I do have a Neptune Passage planner software on my PC which is very very good

That is what I used too plus SWMBO, we would both do a passage plan, then get Neptune to do one and after the trip see which one of the three proferred solutions gave the best answers, ridicule being heaped on whichever did not take us spot on to our target. Folks over here in Disneyland have no concept of cross tides that turn and vary in strength and direction, they just use the GPS and keep adjusting 'till they arrive. :nonchalance: the cruising guidebooks give approx course offsets for crossing the Gulf stream twixt FLorida and the Bahamas for differering boat speeds which is probably ok since the majority will be crossing on fast mobos. It seems very odd to me mind after years of working the Channel tides. WE once met a US crew in Cherbourg who had found the rocks east of the Cherbourg east entrance when crossing from the Solent, WE had a meal with them and they had no idea of navigation as we know it despite that they had crossed the pond in their boat incident free.