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12ft skiffs develop a new boom vang setup

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sargesail View Drop Down
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Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 1:26pm
Actually in the 300 the bend is desirable.
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Post Options Post Options   Quote Guest Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 1:38pm

Originally posted by JimC

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.

Jim,

We use the GNAV on the MPS and I don't see any disadvantage; it allows the goosneck to be at deck level which a a great advantage.

Also you only need to move a very small amount of rope to change the kicker from full on to full off which is a big advantage in a short handed boat.

Rick

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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 2:28pm
Originally posted by Guest#260

We use the GNAV on the MPS and I don't see any disadvantage


I'm sure you don't.

But, for instance, with the same basic layout you could have a tension vang on a radiused track and traveller and the gooseneck on the bulkhead not the mast which would mean you could eliminate the lowers and use a lighter mast section. You'd lose the fuss round the mast and the strut and the whole thing would have lower drag, and the kicker perpendicular to the boom would require even less string.

On the other hand that setup would be not be that much faster - probably not enough to notice against other classes - and much more expensive to build, so it wouldn't be a good option for a one design.

Everything in sailboat design is a compromise. Given the rest of the design decisions in the Musto Skiff the compression vang looks like a good option, like the RS300 I mentioned. On my last Cherub, with a mast stump, permitting no lowers, and the need to get my fat head under the boom, it would not have been a good option.

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Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 7:44pm
Putting the mast of the stump complicates the whole lower mast bend and I do not think works unless you have shrouds going to the spreader roots

I bet you would be supprised how much the stump on your old boat moves about under kicker loads, it could even be more than an equivalent hogg stepped mast. thanks to loosing the stiffness of the mast at goosneck level.

Having lowers is also usefull to allow you to tune the bend in the lower mast.


If it doesn't break it's too heavy; if it does it wasn't built right
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 8:53pm
Originally posted by Granite

stump... I do not think works unless you have shrouds going to the spreader roots

Which it has, being based on an R rig.
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Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 06 at 10:18pm
Originally posted by JimC

Originally posted by Granite

stump... I do not think works unless you have shrouds going to the spreader roots

Which it has, being based on an R rig.


I know, but shrouds going to spreader roots are quite long compared to lowers going to goosneck
If it doesn't break it's too heavy; if it does it wasn't built right
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