12ft skiffs develop a new boom vang setup
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=1515
Printed Date: 15 Aug 25 at 9:13am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: 12ft skiffs develop a new boom vang setup
Posted By: jimmywalsh
Subject: 12ft skiffs develop a new boom vang setup
Date Posted: 06 Mar 06 at 7:53am
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Stolen openly from the boom that appeared on the 5.5m class yacht Jono Temple has adapted it to provide a revolutionary vang system that 1. Frees up space in the boat 2. Is simple to retro fit 3. Provide more purchase - the angle for the pulleys is 90 to the lever not 45 as per normal vangs 4. Is light 5. Doesn't effect the mast bend the way a ram vang does 6. Requires no extra mast support wires 7. And it works 8. Would work on Alloy booms 9. Would also work on yachts The front strut takes all the comression so should be strong and the back struts are in tension so could be replaced by PBO if you are a weight Nazi. There is more bending moment on the boom so would be worth adding carbon uni on top if your boom bends sith a normal vang. I have a feeling the Temple Vang will spread like wildfire, remember you saw it here first. |
Replies:
Posted By: jimmywalsh
Date Posted: 06 Mar 06 at 7:54am
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Posted By: jimmywalsh
Date Posted: 06 Mar 06 at 7:56am
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Posted By: MikeBz
Date Posted: 06 Mar 06 at 8:57am
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How is this significantly different from just moving your conventional kicker attachment point forward until it's only 8-10" from the gooseneck? Surely the boom is going to have to be massively beefed up to take all the kicker load so close to the gooseneck. Mike |
Posted By: jimmywalsh
Date Posted: 06 Mar 06 at 9:17am
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The further you move your kicker/vang attachment point forward the more purchase you need to get your leech tension and the greater vertical load on your goosneck. This treats the whole boom and vang as one spar and the purchase required is less as the adjustment is at right angles to the spar. |
Posted By: MikeBz
Date Posted: 06 Mar 06 at 10:55am
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OK, I can see that the length of the vang 'spar' (for want of a better description) gives you leverage, hence you need less purchase than for an equivalent string & pulleys kicker (oops, vang) attached to the boom at the same point. However, the boom will still need to be massively strong in this area because of the lever arm that the leach tension has over the vang attachment (simple ratio of the distance from the pivot (gooseneck) to the vang vs. the distance from the vang to the clew of the mainsail - or more correctly to the centre of effort of the mainsail?). Mike |
Posted By: jimmywalsh
Date Posted: 06 Mar 06 at 11:10am
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Our booms are very very stiff Most boats use the CST 95 x 39.5 x 2.2 wall elliptical boom |
Posted By: Presuming Ed
Date Posted: 06 Mar 06 at 1:02pm
| Similar to the system that's been on the XOD that my dad sails. Think it's been on the boat for at least the last 5 years. Minor difference is that on the X, there is a bit L shaped aluminium plate which hangs beneath the boom to take the loads, rather than being built in - not allowed, and tricky with wooden spars anyway. |
Posted By: Norbert
Date Posted: 06 Mar 06 at 1:15pm
| What about stainless steel / aluminium / carbon fibre (which ever) boomerang going from the conventional boom position with the v part of the boomerang angled towards the mast and the tensioning block and tackle at the base. Creates space adds weight. |
Posted By: Isis
Date Posted: 06 Mar 06 at 5:39pm
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Ive been toying with whether or not to gnav or vang my new rig since
about november and after spending about 3 hours talking to the guys on
the I14 stand on sunday and a chilli fueled debate with half the cherub
class the night before id finaly decided im going for a gnav. Not anymore sir. ------------- |
Posted By: carshalton fc
Date Posted: 06 Mar 06 at 8:18pm
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what is the differnce detween this and a gnav? cos they both seem to be the same but this vang is under the boom? ------------- International 14 1503 |
Posted By: Isis
Date Posted: 06 Mar 06 at 8:20pm
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....look a bit closer luke lad.
------------- |
Posted By: laser47
Date Posted: 06 Mar 06 at 9:28pm
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i think thats pretty much the diffence. looks dead interesting though ------------- |
Posted By: redback
Date 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. |
Posted By: JimC
Date Posted: 07 Mar 06 at 12:26am
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. |
Posted By: Blobby
Date Posted: 07 Mar 06 at 3:23am
| Care to elaborate? |
Posted By: Chris Noble
Date Posted: 07 Mar 06 at 7:17am
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yeh what are the disadvantages? ------------- http://www.noblemarine.co.uk/home.php3?affid=561 - Competitive Boat Insurance From Noble Marine FOR SALE: I14 2 Masts 2 poles 3 Booms, Foils Kites/Mains/Jibs too many to list. |
Posted By: Blobby
Date Posted: 07 Mar 06 at 10:22am
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just for the techno-freaks this is what happens to all the loads compared to a normal kicker...
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Posted By: Skiffe
Date Posted: 07 Mar 06 at 12:07pm
Some one had far to much time on their hands ------------- 12footers. The Only Way to FLY Remember Professionals built the titanic, Amateurs built the ark. |
Posted By: JimC
Date Posted: 07 Mar 06 at 12:35pm
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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. |
Posted By: sargesail
Date Posted: 07 Mar 06 at 1:26pm
| Actually in the 300 the bend is desirable. |
Posted By: Guest
Date Posted: 07 Mar 06 at 1:38pm
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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 ------------- |
Posted By: JimC
Date Posted: 07 Mar 06 at 2:28pm
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. |
Posted By: Granite
Date Posted: 07 Mar 06 at 7:44pm
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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 |
Posted By: JimC
Date Posted: 07 Mar 06 at 8:53pm
Which it has, being based on an R rig. |
Posted By: Granite
Date Posted: 07 Mar 06 at 10:18pm
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 |