Sailing to weather

[trashpad]

I sailed to Haver de Grace this weekend and the trip back the wind was all on the nose. I had all day to make the trip so I dug out an old sail trim book I had with me and played around. I was able to sail at 35 degrees and get up to 7.5 kts on the GPS with it blowing 10-12 true. The biggest help was getting the Main flat. A lil outhaul, make shift Cunningham, Backstay snug, main sheet tight, and the traveler close to center but just before it back winds off the jib. The head sail was easy, set Otto to stay at 35 and tighten until the weather tel-tails just stop dancing and start to lay.

@ Ron,

Could you write something about sailing to VMG? You had something in the old forum if I remember correctly.

[Ron]

Kurt -

No big secret. In this case velocity is a vector with x and y components. Say y is the straight line from where you are to the next waypoint or marker. x is the right angle portion if you can't sail on that line. Your actual course, assuming you cannot sail directly to the mark, is the hypotenuse which forms the triangle (actually 2 triangles because of the required tack) and it's value is the square root of the sums of x squared and y squared. To get to the waypoint quickest you have to maximize the y component of the triangle, so solve the equation for 'y", and it's called Velocity Made Good, or VMG. To simplyify it, traveling at 6 knots directly to the waypoint would yield a y value of 6 and an x value of 0. Falling of by 30 degrees may increase your actual speed (along the hypotenuse) enough to make y equal to 8, thereby getting there (with a tack somewhere in the middle) quicker. You can use trig functions such as sine and cosine too. In actuality, especially in a race, you would probably be comparing angles which are 35 or 40 degrees to the mark (or wind) to maybe 50 or 60, but it's the same math. This works going away from the wind as well, just steer higher instead. And it works on ANY boat, but multihulls can take advantage of this more than others, because of the bigger increase in speed as we fall off heading into the wind,or sail higher going away from it.

What - you don't want to carry a 60 function scientific calculator on board in the cockpit? Not waterproof? Most of the chartplotters and gps's these days have VMG built into it. It's display is hidded somewhere in the menu. You would need to have the waypoint(s) (and possibly the course as well) entered and then, as you round marks or change direction, you VMG will be displayed on the screeen. Steer a little higher and lower to figure out how to increase it. When to do the required tack(s) is something you have to learn - and that includes factoring in current and possible future wind shifts.

One other note. Filling out the polar diagrams that are printed in the back of the owners manual will give you a good idea what the boat is capable of doing with different wind angles and at different wind speeds. It's not VMG, but it will give you a jump on the competition because you will know what speeds the boat is capable of doing.

[trashpad]

The ST-60 Wind has a VMG but I have not been able to find any info in the manual about the function. I assume that it tells you speed in the water to 0 degree apparent/true wind.

[Ron]

It must be getting some data from the gps on the network. The wind instrument and knotmeter really have no idea where you are going (and both are involved in the solution), so it's getting something down the cable - either VMG itself (an NMEA "WCV" - waypoint closure velocity sentence) or the data to calc it. I've never used the wind display for VMG - my Standard Horizon plotter puts the number on the data line if I want it there. I'm sure that every other decent unit will do the same. I have hand-helds which do it too, but only based on magnetic course. A chartplotter wired up into the network is getting data from both the knotmeter and wind display and can do more. How did Columbus make it here without stuff like this?

If the wind instrument is producing a VMG without a gps and destination on the network, it must be relative to the wind direction and with help from the knot meter. I'd rather see a VMG based on waypoint.

[wingman]

Another useful result of VMG is determining the current. In our recent race, we were hugging shallow water due to an adverse current in the ship channel. However, current does not know or care about channel markers, so we used VMG to tell us when we were getting into the flow. When we got a sudden drop of 0.5 knots, we knew to tack back inshore.

We have also found that in very light wind having a loose jib halyard is very important for speed and pointing.

John

[Ron]

John -

Just about every sail control should be "looser" in light air, and that includes both halyards, both sheets, the main outhaul, the small lines that control the shape of the leech and foot, etc. Loosening the main sheet should be accompanied by pulling the traveller car over towards windward to compensate. You want to boom to rise, not to swing further out.