Clip source: Using VMC polars

So far we’ve only hinted at ways to use the VMC polars while starting to try to explain the concepts. The printed polars give you a couple of advantages, and there are two main ways to use them for "no math" navigation. Advantages for normal use are that they are bigger, and that there are more wind lines to help with planning.


I suggest two ways that they can be best used to find the best VMC angles for a given target. The first is to lay the polar over the boat (or over your position on a paper chart in rl) and align it to the wind, as in the previous VMC examples. The VMCmax is the point on the polar that is furthest toward your target – TWA 50° in the example we’ve been using, for a target of 30° off the wind.

I find that I can see through the polar well enough even printed on regular paper, so long as the room lights are dim, but printing on thin paper or better yet transparencies would work better. Another option might be to wax the polar… rub with candle wax and iron (don’t use the "good" iron if you know what is good for you). Rubbing in a very dry coat of salad oil works too.


The other method makes use of those radial "spokes" that are a prominent feature of the polars posted here. The spokes trace lines of maximum VMC for given target angles relative to the wind. The heavy lines are for targets of 0-90-180°, while the solid and dashed lines mark of 30° and 10° intervals respectively. We’re used to finding VMG, so you can see pretty quickly that the 0° spoke just traces those points (remember that VMG is just a special case of VMC). If you rotate the polar, you can see that the spokes always point to the point furthest "up"… max VMC!

In our 30° example, you pick the 30 line (first solid line counting clockwise) and read off the TWA where it intersects your wind line. Like magic! You get the same 50° answer as the overlay method.

Using the VMC spokes is a particularly good way to work out a set of delayed commands for those awkward times when you have to sleep. It is easy to pick a TWA to about a degree of accuracy just by eyeballing the polar. Believe it or not this is better than most routing software will give!

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