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-   -   Attachment method for Vang (http://www.sailnet.com/forums/gear-maintenance/38564-attachment-method-vang.html)

KeelHaulin 11-17-2007 12:09 AM

Attachment method for Vang
 
I'm going to add a standard (non-supportive) vang soon and I was wondering what the best way to attach the block at the mast would be. We have an un-used bail on the boom 1/3 of the way back from the gooseneck that will work for the vang. At the mast I could either use a padeye or a pole ring. The pole ring looks stronger; we had a padeye rip out in a mildly uncontrolled gybe (preventers are going on soon also).

I was considering the Ronstan RF41 if it has the right radius to fit the mast.

http://shop.sailnet.com/product_info...oducts_id/4964

Faster 11-17-2007 12:23 AM

There can be a tremendous load on that fitting under heavy going... It will be difficult to make either of those types of fittings attached sufficiently strong.

We had a fitting that bolted to a long slug that slid into the sail track groove and locked in place. It was identical to the gooseneck pivot, so the rotation of the boom and the vang fitting matched perfectly.

This was on a 24 foot day racer.



http://i213.photobucket.com/albums/c...er345/vang.jpg

Hopefully you can make sense of this... If the attachment bolts (which thread through the long slug) are long enough that they will pass through holes drilled in the back of the sail track as shown, the fitting will never move.

I believe this was a commercially available fitting, but we have had a machinist make one of these as well.

Sailormann 11-17-2007 12:36 AM

How big is your boat/sail ???

KeelHaulin 11-17-2007 01:34 AM

The sail is 350 sq-ft, a bit on the small side for a 41' boat. We do get into heavy wind on SF Bay. Harken Compu-Spec gives blocks rated SWL of 1500 lbs; break strength of 3050 lbs. Is something wrong with this load spec?

sailingdog 11-17-2007 08:38 AM

Given that the vang attaches mid-boom... you might want to go a bit stronger on the blocks... and I'd have to agree that a simple padeye or pole ring isn't going to be sufficiently strong. You need a boom bail or something similar that is through bolted.

NOLAsailing 11-17-2007 10:19 AM

Quote:

We had a fitting that bolted to a long slug that slid into the sail track groove and locked in place. It was identical to the gooseneck pivot, so the rotation of the boom and the vang fitting matched perfectly.
That looks like the fitting for a Boomkicker, which supports the boom like a rigid vang and is used in conjunction with a soft vang. The loads are mostly compressive (see photo for fitting).

http://www.rambunctiousracing.com/images/bk_2.jpg

For a soft vang, I don't think I trust that fitting. On my boat I have a robust plate held in place with 8 or 10 rivets. The vang can really load up, don't undersize this fitting.

http://www.rambunctiousracing.com/si...ng-600x450.jpg

Faster 11-17-2007 12:42 PM

Quote:

Originally Posted by NOLAsailing (Post 224275)
That looks like the fitting for a Boomkicker, which supports the boom like a rigid vang and is used in conjunction with a soft vang. The loads are mostly compressive (see photo for fitting).

http://www.rambunctiousracing.com/images/bk_2.jpg

For a soft vang, I don't think I trust that fitting. On my boat I have a robust plate held in place with 8 or 10 rivets. The vang can really load up, don't undersize this fitting.

http://www.rambunctiousracing.com/si...ng-600x450.jpg

Nola - the attachment method is the same as I described above, but there is an essential difference in the outer fitting. As a gooseneck/vang attachment it is important that the fitting conforms to the mast shape in such a way as to compress the edges of the sail track against the inner slug so as to prevent the sail track from "peeling" open under load. Without those "shoulders" to trap the extrusion, you're right, under tension it may be subject to failure if sufficient load was applied.

In my experience on 40 footers these types of fitting are often welded onto the mast to avoid issues of fastener failure. But our old 24 foot (SA/D =29 - fairly powered up) racer used the fitting described above for both gooseneck and vang. Some early models that used a through-bolted bail at the partners for the vang suffered mast failures.

KeelHaulin 11-19-2007 01:06 PM

So the greater issue is fasteners stripping out? That makes sense; but unfortunately I don't have a mast that has an extruded track in it; so that type of fitting is not going to work. Looks like I will either have to beef up the holding ability of the pole ring or design something that will have enough holding power.

Thanks for the help...

Giulietta 11-19-2007 01:37 PM

Keel,

For a bot your size, I think you should invest some money and have a metal shop fabricate something like this for you.

Its is simple a Plate is bent to conform to your mast radius, then a hinge is welded above and bellow and tube with the fitting is held by a bolt.

Its very simple. Look at mine. You then attach with bots or rivets.

http://i212.photobucket.com/albums/c...tacsc2/1-5.jpg

http://i212.photobucket.com/albums/c...ttacsc2/12.jpg

Giulietta 11-19-2007 02:26 PM

I made also this drawing for you.

http://i212.photobucket.com/albums/c...tacsc2/1-6.jpg


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