Moving up.....

HI

Hi

1REO wrote: I have only been sailing for a year and a half, so my question is: How do you determine the vmg, is this done by any instrument? If so how well does it work if you got a lot of wind shifts, bot direction and speed?

It felt like a revelation when I found out how to use VMG, velocity made good, on my IS15 instruments. For the sake of those who haven't yet discovered this feature, let me elaborate what's already been said above.

The VMG describes the velocity of the boat towards the wind's eye in knots. It should not be confused with the VMG on a GPS which tells you how fast the boat is moving towards a waypoint, i.e. a fixed place on Earth.

The VMG is useful to find the best course to steer if you want to sail against the wind, i.e. tacking, or going with the wind, i.e. running. On all other courses it's the log that tells you when your boat is performing best. If you look at a polar diagram you will find that it looks like an apple. The boat is going slower if you are trying to steer to the wind (towards 0 degrees) or down the wind (towards 180 degrees). You want to find the balance between going directly to your target and slower, or going a longer way but faster.

Since I am from Sweden I have to sail against the wind no matter in what direction I am headed, so the below examples will be about performing when tacking.

The first picture shows the wind instrument and the combi instrument both displaying VMG. You can see that the boat's speed towards the wind's eye is 4,5 knots when I am steering 23 degrees into the wind at a boat speed of 5,3 knots. During the circumstances I would probably make 6,2 knots of boat speed if I steered 35 degrees, but the VMG would drop to 3,5 knots. The trick is to find a nice balance between the two figures. I think other makes of instruments have a different calculation of VMG giving you a "factor" you want to keep as high as possible, but on my Simrad system its the two numbers in knots I have to compare.



The second picture shows when I have set only the wind instrument to show VMG, while the combi instrument is showing other crucial data, like depth. The arrow pointing down on the digital display is indicating that the digital display is showing the velocity toward's the wind's eye in knots and the arrow pointing to right is indicating that the wind angle displayed on the analogue display is Apparent Wind.



Keep in mind that, as opposed to True Wind Angle, you can make the Apparant Wind Angle smaller, i.e. you point higher, by doing one of two things: steer closer to the wind or go faster. The challenging thing is to do both and that's what's been intriguing sailors since the beginnig of time. The True Wind Speed should be independent of what course you steer, while the angle will obvious change accordingingly to the course.

Also keep in mind that the True Wind Angle and Speed is calculated from the wind data your system provides and the boat's speed. It will be hopelessly wrong if you don't calibrate you log several times during the season.

I hope this helps.

Johan

1REO

Regarding a 108%. I currently use this sail for racing on my 400e. It is an excellent size for winds 10 knots and above. Not bad down to about 8. Should use an overlapping foresail really for anything below 8. (I'm referring to racing of course) However, if you're considering something this size you will be interested to know that iIt is too big to use the self tacker track and it needs to sheet to a point forward of the genoa track. On the 400, I put a block in just behind the shrouds and the sheet runs in between the shrouds.

Steve