Comments on: VMC revisited

By: outlaw

outlaw — Thu, 24 Nov 2016 12:54:39 +0000

The one that works. Router helps.
Seriously some common options are
TWD @ next tack – as in the example, and much of the short round the buoys type stuff.
Plain VMG – Vendée style Southern Ocean downwind…
Bearing to primary opponent +- 90. I need to explain that some day.

By: João

João — Mon, 21 Nov 2016 19:53:53 +0000

VIva Outlaw.

Which takes us, the “…constant VMC target”, to the million Euros question: “B”, where is it? or, as already mentioned the router talk.
Big Hug.

By: outlaw

outlaw — Mon, 21 Nov 2016 10:39:40 +0000

Viva Joao.
You are correct, if overthinking things a bit. One needs to understand that in the 6 hour timeframe the difference between “constant course” or “constant TWA” and a “VMC course with a constant target” can easily be minutes on the hour. It’s possible to get a little edge with a “VMC course with a floating target”, that is at best seconds on the hour. As such I think that a constant VMC target for each 6 hour wx window is perfectly adequate.
And of course that still leaves the matter of “where do I want to go?”, which is a rather big deal.

By: João

João — Sat, 19 Nov 2016 16:10:16 +0000

Viva Outlaw and all.

The example you gave here is the simple case of finding VMC (Velocity Made good on Course) when we only have two marks to compulsory pass, a Start Line (in SOL, a Start Waypoint) and a Mark to round (in the example, also an Island). Let’s call it the “VMC, A to B” case.

Assuming now the following simplifications:
1 – The weather is continuous in time and space;
2 – You don’t have “Water” and “Hull” induced effects (the SOL case, again),

there is only one solution that minimizes the sailed time from “A to B”, or by other words, only one path that maximizes the “VMC, A to B”.

Let’s also remember that “VMC” (in general) depends not only on the boat characteristics you sail (TWS;TWA -> BS or the Polar), but also on the target you want to reach.

If for a short distance, like the one you gave on this example, it is pretty obvious the VMC solution and respective conclusions, for a longer path, in open waters, without any geometric limitations (ex.: race marks to round) exception made to the ones imposed by having land, and a changing Weather, the simplicity of the solution of your example is not so immediate.

To where do I sail or, where is the next point “B”, is the big question?

Again, this will takes us to the router talk.