Vang Spreader

[Doug Lord]

Invented by Dave Lister(as best I can tell) and used on some Moths.
Here is an explanation by Phil S on DA:

The vang spreader was first used by Dave Lister, maybe 3 years ago. Works like any spreader on a mast. Widens the staying angle to reduce loads on components. It allows the vang strop to be attached further aft on the boom so that for the same boom section capacity you can get greater leach tension. It slightly increases the moment arm of the vang system so gives the vang more power too.
Basically increased vang power from existing boom sections and tackle.

Luka's boat is a work of art. Hundreds of hours by Luka and Marty in tooling and crafting a masterpiece. Marty's version will be ready in a week or so. These guys are not speedy builders but they set a high standard to follow. Lots of interesting tricks in the details are worth looking at.

Phil S
Moth AUS 3574, My moth Blog
IC/DC AUS 21, My Sailing Canoe Blog
2011 Moth Worlds Belmont NSW
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http://www.luka-damic.com/

Picture from Luka Damics blog of his vang spreader:

(click on image)

[cardsinplay]

It also puts more load on the boom gooseneck, adds weight to the boat and additional components requiring maintenance. As to the added function as a benefit, we'll just have to wait and see when the boat is sailed against the best rigs on the beach.

Then, there's also the reality that many of the best Moth riders are going to hard wings, making this vang approach old school before it gets to school.

[gonzo]

That's been used for decades.

[Doug Lord]

Originally Posted by gonzo

That's been used for decades.

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Any links/pix of other examples?

[CutOnce]

Temple vang

[Doug Lord]

Not the same but very interesting...

[Landlubber]

..the Sydney 12 footers are a radical bunch of nuts....i used to sail an 18, though we were pretty good, but watch the 12's for a few hours and you soon realise we were playing with ourselves, they really know how to sail to the X factor.......unreal to watch, but alas, I have never sailed one (did sail an 8 footer once at Woolwich, now that is simply stupid, 4 man boat).......

[waikikin]

Originally Posted by Landlubber

..the Sydney 12 footers are a radical bunch of nuts....i used to sail an 18, though we were pretty good, but watch the 12's for a few hours and you soon realise we were playing with ourselves, they really know how to sail to the X factor.......unreal to watch, but alas, I have never sailed one (did sail an 8 footer once at Woolwich, now that is simply stupid, 4 man boat).......

Right on the money LandLubber http://www.skiff.org.au/photos/hotshots.htm check some of these shots for fun. Sailed along with(overtaken by) some replica 18's last weekend in the Balmain Regatta, there was one or two of the vintage 10's out too. You've only gotta look back in time to find a lot of this "new stuff" even the one footer/bugs & such in Aus exibited some of the "modern" concepts, like a workmate said "we can do stuff from the past, but we cant nessesarily do stuff from the future back in the past! I think he might be a budding Rap artist. All the best from Jeff.

[Landlubber]

...hey, don't ya just luv it when the boat goes out of control, but is still upright!

I did that to the Bundeena ferry years ago with my Contender (KA2, Craig's first production fibreglass one)....I was only a skinny little fella then and a southerly came in that I simply could not resist, they backed up and the paggengers cheered as I "sailed" by, the rudder and c/board the only things that occasionally hit the water....Ya got ta luv 'em.....

[gonzo]

It is a strut in a rigging part. Spreaders, dolphin strikers, etc. are all the same type of structure.

[Doug Lord]

Originally Posted by gonzo

It is a strut in a rigging part. Spreaders, dolphin strikers, etc. are all the same type of structure.

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The use of such a structure as part of a vang seems to be regarded as new in the Moth class which has been around for a while.....Have you ever seen a vang designed like the vang in the first post?

[fastwave]

No I haven't,
but I like it. If i did it, I would improve it by replacing the stay with a carbon rod perhaps. Wait a minute. Then it would be an A-frame like the tempest.

Old idea perhaps

[philSweet]

Works like any spreader on a mast.
Widens the staying angle to reduce loads on components.
It allows the vang strop to be attached further aft on the boom so that for the same boom section capacity you can get greater leach tension.
It slightly increases the moment arm of the vang system so gives the vang more power too.
Basically increased vang power from existing boom sections and tackle.

I'm not buying any of these explanations. Not as actually executed on the boat.

1. Show me a mast with the stay attachment point half the distance to the load center with a spreader below that.

2. There will not be any load reduction except for a slight lessening of compression between the strop and the strut. The bending moments will increase at the strop and the strut. What will be affected is how the boom bends under load. It will bow down less at a given tension, meaning a stiffer feel and different gust response.

3. I don't see what the strut has to do with the strop location aft. It appears to be limited by the mainsheet geometry. Moving the attachment point aft lowers the tension only a little bit; but it can decrease the bending moment significantly. The ability to move the strop forward without having the boom tip deflection increase is a possibility. That might give more ducking under room during a tack.

4. Ok. The leach tension increase is on the order of 3% as built. It could be more with a different arrangement, so I'm thinking that is not the reason, either.

5. Nope, Static loads are higher. Might be offset by improved stiffness if buckling is a concern; but then dynamic loads tend to increase.

I came up with several different reasons one might want a strut; but when I designed the thing for the desired effect, they came out different from this one. One idea is using a rigidly attached vang strut to limit the amount the boom can roll about its axis- A solution looking for a problem.

[Doug Lord]

Phil, can you post an illustration of your idea?

[philSweet]

Its just an effect of the geometry. Any rotation of the boom will move the end of the strut out of the plane formed by the gooseneck and the two attachment points. This will lengthen the path of the vang. You could use a line to the strut as a vang tweaker, or just let the vang hold the strut and thus limit boom roll to small angles. The attachment of the strut to the boom has to be rigid transversely. The strut doesnt have to be pushing the vang downwards for this to work. In fact, the effect is probably at a maximum if the vang is straight. On the moth, it appears the boom is pinned to the mast, preventing any roll. But the booms on many boats pivot freely.