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12ft skiffs develop a new boom vang setup

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carshalton fc View Drop Down
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Post Options Post Options   Quote carshalton fc Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 06 at 8:18pm
what is the differnce detween this and a gnav?  cos they both seem to be the same but this vang is under the boom?
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Isis View Drop Down
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Post Options Post Options   Quote Isis Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 06 at 8:20pm
....look a bit closer luke lad.
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Post Options Post Options   Quote laser47 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 06 at 9:28pm
i think thats pretty much the diffence. looks dead interesting though
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Post Options Post Options   Quote redback Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 06 at 11:28pm
Hey if there is too much strain at the root of this strut thing you could run a wire to an anchorage further back on the boom to take the forces!  Better still go for Gnav and with some good engineering you could get it to support the weight of the boom and lessen the leach tension in light winds.
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 12:26am
Originally posted by redback

Hey if there is too much strain at the root of this strut thing you could run a wire to an anchorage further back on the boom to take the forces!


That would rather miss the point. There are quite a few disadvantages to the compression vang setup (most of which don't apply to a one design to be fair). I'd need a lot of persuading to use one.
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Blobby View Drop Down
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Post Options Post Options   Quote Blobby Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 3:23am
Care to elaborate?
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Chris Noble View Drop Down
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Post Options Post Options   Quote Chris Noble Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 7:17am
yeh what are the disadvantages?
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Post Options Post Options   Quote Blobby Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 10:22am

just for the techno-freaks this is what happens to all the loads compared to a normal kicker...

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Post Options Post Options   Quote Skiffe Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 12:07pm
Originally posted by Blobby

just for the techno-freaks this is what happens to all the loads compared to a normal kicker...

 

Some one had far to much time on their hands

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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 12:35pm
OK, Disadvantages of the compression vang. Bear in mind that not all of these apply to every boat and the extent to which these are issues varies from boat to boat. Sailboat design is always a compromise, and doubtless there are situations where the compression vang is the best solution. On a one design many of the disadvantages are irrelevant as all boats are the same.

1) Mast is pushed forward by the vang well above the gooseneck. This will require either staying or else a very stiff mast section. On a tension kicker the gooseneck can be off the mast, and thus the forward push taken out of the mast. In any case if the gooseneck require staying then the stays are much shorter and create less drag.

2) The compression strut affects airflow round the sail reducing power and creating drag. Even the Bethwaite dual luff setup (illegal on most classes) is a compromise and is also a pain to rig.

3) The arrangements nevcessary to stop the vang pushing the boom off the gooseneck are a nuisance

4) Its possible to arrange mast support with a tension kicker so that lowers are unnecessary, for instance with the mast stump used by some 12s and Cherubs, or the gooseneck on the front bulkhead like Moths. This reduces drag still more and makes it easier for the crew to position in front of the shrouds.

For balance, the chief advantages include
room under the boom
the boom can be as low as desired
no concerns about clearance for the kicker in internal layout.

RS300 is an example where the advantages probably outweigh the disadvantages, as the bend issues are less of a concern on an unstayed spar, and the very low boom with its aerodynamic advantages is made practical.

Edited by JimC
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