vang question

[navahoIII]

Fellow Daysailer sailors,

The boom vang we bought from D&R Marine stipulates that it should be attached 28 inches from the front tip of the boom (for the DSI). And, as I understand it, it is supposed to be angled at 45 degrees to the mast.

If it is not possible to have both conditions met is one more important than the other? In other words is 45 degrees crucial, or, is it best to have the 28 inches along the boom? Can a compromise be made?

Also, the vang has a very long wire (about 12 inches), which I think is unattractive, on one end that connects with the boom. Is there any reason why it cannot be shortened to around 2 inches instead?

Thanks.

[Roger]

The distance is more important than the angle. I had a short piece of wire on mine, but placed it at the bottom to keep the fiddle block up off the deck and make it easier to cleat. I think the wire was about 6" long.

[navahoIII]

Thanks, Roger, it makes sense that the distance is more important.

So, do you think it would hurt to shorten the wire -- there is plenty of line on the vang that could span the distance plus have enough to work with?

[kokko]

THere is a trig solution to this problem. I looked at three arrangements:

1. THe vang pulls straight down: 90 degrees from the boom and parallel to the mast
2. Vang mounted 45 degrees from mast and boom - assume 2 ft out and two feet down
3 Vang mounted 60 degrees from the boom and 30 degrees from the mast.

The best is #1 - all the force is directed to pull the boom down. # 2 is next best and #3 is last

[GreenLake]

THere is a trig solution to this problem. I looked at three arrangements:

1. THe vang pulls straight down: 90 degrees from the boom and parallel to the mast
2. Vang mounted 45 degrees from mast and boom - assume 2 ft out and two feet down
3 Vang mounted 60 degrees from the boom and 30 degrees from the mast.

The best is #1 - all the force is directed to pull the boom down. # 2 is next best and #3 is last

You don't write whether you are keeping the attachment point fixed on the boom or on the mast. That makes a difference in the results. #3 is only the best if you allow the position on the mast to move (to about 3.5 feet).

If you keep the attachment point on the mast fixed, but vary the attachment point on the boom to get the same angle, #2 would be the best. Yes, you are pulling downward more in #3, but on a shorter lever.

There's an interesting result when you run the trig: for each location of the atachment point of the vang on the boom, you can vary the attachment point on the mast whichever way you want and the force *sideways* on the mast is unaffected (depends only on the force the sail applies to the boom).

That's most likely the reason why Roger writes that the location of the vang on the boom is the more important variable: it fixes the ratio between force on the sail and sideways force on the mast. For 28" on a 10' boom, the ratio is 4, assuming that the sail force is effectively all applied at the end of the boom. You can vary the angle to the mast without affecting that ratio.