There's a general rule of thumb for locating the vang. The ideal placement forms at least a 45 degree angle between the vang and the boom. Same thing for the angle between the mast and the vang.
The reason for this is that you want a vang to pull downward. Any angle narrower than 45 compresses the boom more than it pulls it downward.
Sometimes, it's impractical to place the attachment points so that you have a 45 degree angle. In that case, an angle of no less than 30 is a good compromise.
45 or more degrees at the boom end of the vang is good, less than 30 degrees is hardly worth it...
Regards,
Judy B
In a message dated Thu, 9 Sep 1999 12:24:34 AM Eastern Daylight Time, BrennanPM@aol.com writes:
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> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
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> Having just assembled an "el cheapo" boom vang, I had the same question Mike
> did - where should it be attached to the boom.
>
> I found a pair of 1/8"circular marks 1 1/2" apart on the bottom of my boom
> centered 28" back from the gooseneck end of the boom. The circles look like
> pencil marks but they are probably 24 years old. My guess is they were put
> on every boom by the manufacturer as a guide for vang placement. Does anyone
> agree?
>
> I also found two more pairs of circular marks on the sides of the boom
> centered 4 1/2" in from the clew end. On the starboard side the marks are
> 7/8" apart and on the port side they are 1 1/2" apart. Any idea what these
> might be for? The only attachments on my boom at the outboard end are an eye
> strap on the top for the outhaul and an eye strap on the bottom for the end
> of the main sheet.
>
> Pat Brennan P15 #621