Vang Attachment Hints

JBlumhorst@aol.com
Thu, 14 Jan 1999 10:26:25 EST


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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In a message dated 1/14/99 6:47:43 AM Pacific Standard Time,
bsnavely@alveus.com writes:

> 2. Installing a boom vang, I have the boom vang, how is it attached to the
> mast and where, how far out on the boom do I install an eyestrap and is
this
> the right thing to use?

Hi Bud

The vang is best attached to the boom with a U or V shaped bracket called a
bail. It should be attached so that it forms an icsosoles (spelling!)
triangle, with the distance from the gooseneck to the mast attachment point
approximately equal to the distance from the goosneck to the boom attachment
point. If you prefer, you can make the distance along the boom a little
longer than the distance along the mast, for better leverage.

The vang is one of the most stressed attachment points in your whole rig.
Therefore there are some rules that you HAVE to follow if you don't want the
bail to pull out of your boom or get bent.

The boom bail should be installed at a 45 (or so) degree angle to the boom;
the key point is that it should point directly at the place the vang attaches
to the mast when the boom is level. The U or V should be attached to the
sides of the boom, not the bottom, so that the force on the rivets/screws is a
shearing force, not a tensile/pulling force. A tensile force will pull your
fastener out at the worst possible moment.

This is one of the few places on your rigging that it's NOT a good idea to
through-bolt thru the two attachment points on the boom. The force on the
boom is enormous there, and you don't want to concentrate it even more when
the boom is outboard by having a bolt thru the boom. Also, if the bail is
attached to the sides of the boom, it's a shearing force, so there's no great
advantage to thru-bolting.

As the boom swings outboard, there will be alot of twisting force on the bail.
You should use a twist shackle to atatche the block in order to accomodate it.

The same ideas apply to the mast attachment point. You should attach the mast
bail so that it points at the boom attachment point. You should attach the
vang block so that it can swivel in both the vertical and the horizontal plane
to line up with the boom block.

One of the nicest ways to attach the vang to a small diameter mast is to put a
strong (welded) 3.5 inch stainless steel ring around the mast a few inches up
from the base. Attach it with a single eyestrap at the forward side. The
ring can move up an down to accomdate different angles of the boom. Attach
the vang with a shackle to the ring. The vang can slide around on the ring to
line up perfectly when the boom is outboard. The load on the boom attachment
point (the eyehook) is negligible, with the mast itself taking all the load.

Be sure to get proper strength blocks and set up enought purchase. I
recommend 6:1 or 8:1. The reason is this -- if a sail control is easy to use,
you will make frequent adjustment. If it's hard to use, you won't even try.

If you need some ideas on how to rig it, check out the back of the Harken
catalog. they have suggestions, including the correct strength blocks. If
you want a drawing of the ring idea, including how to set it up so it detaches
easily, send me your fax number and I'll send it. I use an elegantly simple
8:1 system on my racing dinghies.

An additional consideration -- you want to be able to detache the vang easily
without removing the line so you can trailer it.

Judy Blumhorst, DC
WWP-19 #266 "Red Wing"
SF Bay, CA