Guys, my apoligies for weighing in later in this thread. That said, there are several key things as yet unmentioned, which have very big factors on which tack you want to choose, when, & why.
And yes, the tacking on the shifts, etc. is important, particularly when racing
. Especially in waters with no hypothetical currents, or where you & your competitors are all sailing in basically the same weather
system & waters. But... having raced hundreds of thousands of ocean miles, I can say that there's a lot more to it than that, when trying to get somewhere. Even when racing
And such is where the info in my below thesis, was learned. Or rather, tuned, & put into practice.
As lots of quality studying on the topics herein, are a Big help. But can comprise a good bit of time, & expense (plus headaches). That, & victories too, for the astute. Yea!
Firstly, & this may sound a bit wild, but which tack is your boat faster on?
As yes, there are a surprisingly large number of boats which will point significanly higher, & be much faster, on one tack vs. the other.
And not just upwind, but reaching & off of the wind
as well, with various sail combinations, & in varying wind
Like my Dad's old Cal 29
for example. Upwind, she was almost a knot
faster on one tack than on the other. Which, sadly is often due to manufacturers cheaping out, when building boats. Doing things like pouring the lead for keels, with the molds laid on their sides, vs. being vertical.
So that you wind up with much more ballast, & thus sail carrying ability (speed) on one tack vs. the other. Ditto on other; hull
, & rudder
building methods; etc. etc.
So it pays to take your boat out in different types of conditions, with different sail combo's, & test out your boat's true speed, on both tacks, at the same AWA, & thus, come up with a TRUE set of Polars for her.
As a half a knot
of difference, can mean big gains or losses, depending on whether you're on starboard or port. In terms of getting to Bora Bora
, ot making it into that favorable weather system or current
, on/in which, you'd like to hitch a ride.
Also, I know that current
has been mentioned, in terms of staying in it or out of it, depending on whether it's a help or a hinderance; regaring where you're heading.
But another Huge factor with regards to it, is that there are plenty of circumstances in which you might want to stay on an unfavored tack for a day, in order to get into or out of a certain current.
As the gains made by finding "favorable waters" (or winds/weather) are major, when compared to losing 10nm, due to staying on an unfavorable tack for a day.
Doing so can add (or subtract) a knot or two (Easily) from your VMG. For a much bigger part of the picture (passage), in terms of reaching your destination
So... when you're down below "Naviguessing", you'll want to pull out you;
- Pilot Charts
- Ocean Sea Surface Temps (reported), so as to know the true positions of currents, & to some degree weather systems (& their intensities, vs. what they're reported to be).
pics of the weather systems, including temps, & moisture levels. Plus the same goings on in the things which affect weather systems, big picture wise. Like land mass temps, within a few dozen, to a few thousand miles of the big weather systems, & where you're headed. Especially ones with significant topographical features... Deserts, Mountains, Major Valley Systems & Mountain Passes, etc.
- Typical area Wind Patterns for the grid you're in; & those that you'll be crossing, & or aiming for (plus those of the above topo features).
- Reported Winds for same. And their variance patterns; both strength, & angle alterations. Be they cyclical repeating, or other.
- Reported Current locations & Strengths for grids X, Y, & Z (above). And again, their movement patterns of note.
- Ditto on what the weather systems are doing now in the same grids.
- Also, the weather forecasts for the same locales. Preferably from more than one source. As different weather bureaus/MET have differeing levels of (monitoring) assests in area X, or Y.
That, & varying levels of expertise on making predictions for said areas.
Meaning that, for example, you wouldn't expect a Hawaiian forcaster to be an expert on weather goings on, in Antartica. Where as you'd better trust the guys in New Zealand
, Tierra del Fuego, or even better, McMurdo Station, for same.
Then, when you have all (or most) of the above data & info in front of you, comes the Art & Science of distilling it all into an optimum (weather routing) track for your vessel. So that you can better choose which tack(s) are the best, big picture wise.
Basing it on your likely boat speed, for the AWA headings which your entertaining. And using that, plus all of the environmentals, deciding which route(s) - Plan A, B, & C, are the best for you to take, in order for you to maximize your best speed to get to your destination
So, yeah, you're both looking 2, or 10 miles down your intended track, at conditions, & what tack to best be on. Plus also, anywhere from 50nm to several hundred nm ahead. In order to best pick your most desirous conditions (& to avoid the bad stuff).
Ergo, a GOOD understanding of how the weather works, & all that goes into forcasting such, is cructial.
Also, to assist you with this, there's a good bit of software
out there. Primarily targeted for racers. But as usual, it's trickle down tech.
That, & you can hire the services of professional weather routers. And they can tailor how much info that they lay out for you, based on how much data you can give them on your boat, including your real world Polars. Plus, how much you want to spend on their services. And give you very good routing suggestions.
Some of their reports & suggestions are Incredibly
accurate & detailed. Being able to tell you what will happen in your area withing the next few hours... & (further) on down the line. And they'll even tell you when best to tack or gybe, even though it may (temporarily) put you on the (hypothetically) unfavored wind angle. In order to get hooked up with the best weather system in order to speed you towards paradise.
And most folks that use them, have found the services (of good ones) to be well worth it, particularly for long passages. As it helps them to optimize their speed, as well as comfort, in addition to keeping them out of the nasty stuff (& reducing wear & tear on the boat + the crew).
So, yeah, there's a Lot more to choosing the best tack, than just banging them out, on the 2 degree shifts.
It's a lot easier for the helmsman, or on watch person, to be able to see such wind changes, with properly
calibrated instruments; on deck
, & at the nav station. Ditto on having other accurate
instruments, like water
temp measurements, & a good
And even just a good pair of digital compasses will let the helmsman spot a 2 degree lift
or header, where as, seeing such (especially @ night) on a regular compass
card isn't nearly so easy. Especially for neophytoe type crew members.