Why is this fast?
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=2161
Printed Date: 16 Aug 25 at 11:43pm Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Why is this fast?
Posted By: Guest
Subject: Why is this fast?
Date Posted: 04 Sep 06 at 10:23am
I guess it must be but I don't undetand why it is fast to have the mast so far forwards - I would have thought 90 degrees to the wind on the run would be best for maximum projected area ...


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Replies:
Posted By: BBSCFaithfull
Date Posted: 04 Sep 06 at 10:31am
It moves the centre of effort towards the water etc etc.
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Posted By: Guest
Date Posted: 04 Sep 06 at 10:35am
Originally posted by BBSCFaithfull
It moves the centre of effort towards the water etc etc. |
What?
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Posted By: blaze720
Date Posted: 04 Sep 06 at 11:20am
Wind speed is (usually) progressively stronger above the waters surface and could be less turbulent as well. Sailing in this manner therefore projects more of the sail area higher up into 'better' wind. It also balances the rig about the centreline in a way a symetrical spinni would do in many other classes. Perhaps a Star pundit can comment on whether the hull produces less drag when digging in the windward chine. Possibly a combination of all three (and other) factors. Other non spinni classes do it as well without a keel .... OK, Finn, Laser spring to mind and even the Blaze can benefit offwind in lighter stuff sailing by the lee, going deep and with the rig over your head canted at an angle !
Blaze 720
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Posted By: Stefan Lloyd
Date Posted: 04 Sep 06 at 11:27am
Blaze720, I think you are misunderstanding the question, which was: why is the rig raked forwards downwind. You are talking about heeling to weather.
http://www.sailinganarchy.com/forums/index.php?showtopic=40499 - http://www.sailinganarchy.com/forums/index.php?showtopic=404 99 is talking about this subject at present. Quite a few keelboat classes do it. So do Merlins, although not to the degree Stars do.
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Posted By: Stefan Lloyd
Date Posted: 04 Sep 06 at 11:49am
Originally posted by turnturtle
Shrouds conventionally prevent the boom from extending a full 90deg to the mast downwind |
Only on rigs with swept-back spreaders, which applies to all stayed dinghies I can think of and a lot of keelboats but not, I believe, Stars. Some keelboats, such as Stars, have in-line speaders in order that the boom can go out to 90 degrees and rely on the runners to stop the mast toppling forwards.
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Posted By: Guest
Date Posted: 04 Sep 06 at 11:49am
Originally posted by Stefan Lloyd
Blaze720, I think you are misunderstanding the question, which was: why is the rig raked forwards downwind. You are talking about heeling to weather.
http://www.sailinganarchy.com/forums/index.php?showtopic=40499 - http://www.sailinganarchy.com/forums/index.php?showtopic=404 99 is talking about this subject at present. Quite a few keelboat classes do it. So do Merlins, although not to the degree Stars do.
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Quite - why rake forwards to such a large degree?
There is no kite here so what is going on?
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Posted By: Stefan Lloyd
Date Posted: 04 Sep 06 at 11:58am
Rick, I'd suggest reading the thread I referenced. One theory is that is develops a flow over the main. I don't claim to know the real answer, but given the competitiveness of the class, if they do it, I bet it is quick.
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Posted By: Guest
Date Posted: 04 Sep 06 at 12:32pm
Originally posted by Stefan Lloyd
Rick, I'd suggest reading the thread I referenced. One theory is that is develops a flow over the main. I don't claim to know the real answer, but given the competitiveness of the class, if they do it, I bet it is quick. |
No doubt it is fast as all the Star guys do it - I was just wondering if this translated to other classes - e.g. Taser or N12.
I read the SA thread thanks. Some interesting points.
Seems there is two things going on;
1) Raking the mast well forwards
2) Raising the jib
Rick
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Posted By: JimC
Date Posted: 04 Sep 06 at 12:39pm
Originally posted by turnturtle
surely it would be faster... |
I think we can be pretty confident that sailors of the Olympic coffin have a very good idea about what it takes to make the bizarre rig on that bizarre boat go what passes for fast. I have less confidence that such concepts would be transferrable to higher performance boats...
Originally posted by Guest#260
I was just wondering if this translated to other classes - e.g. Taser or N12. |
They're planing boats, not vintage leadmines, so probably not. Also bear in mind the frequency with which Star rigs go over the front...
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Posted By: KennyR
Date Posted: 04 Sep 06 at 12:57pm
It's all quite simple. It develops flow over the main. If the mast is upright or raked back the rig can only develop stalled 'drag' forces, but by raking the mast forward, the air can escape upwards and thus develop flow across the sail. Bethwaite talks about 'roll over vortexes' that work their way up the lee side of a poled out jib, drawing air across it and helping to develop further flow across the main. Personally we have found that when you get the mast well forward and hoist the jib up, there is enough slack in the forestay to start making the jib behave a bit like a spinnaker. Either way it is waaay faster to have the rig forward than not. If you look at the fundamentals of a Star rig, you can appreciate how important this is. For a start the chainplates for the upper shrouds are ahead of the mast, so that as the rig goes forward, the shrounds loosen and the bend comes out of the mast. Also the mast heel is free to move in Derlin or rollers, so that once the mast has hit the front end of the mast gate, the heel can slide back 1"-2" for a bit more forward rake. Thirdly the spreaders are free to swing forwards, so that the leeward shorunds and spreaders do not cut into the main and spoil the sail shape. It is generally best to have the rig max forward in the light [helps keep the boom out too], so that the mast tip is almost over the bow, with a slight inversion in the mast to develop am even better flow and the crew lying on the deck as far forward as he can go [hanging onto the forstay with one hand], and enough heel to keep the tiller neutral. As the breeze comes on everything starts coming back not only to keep the mast in the boat, but to make it controlable [think laser with no kicker downwind]. Have a look at http://www.quantumsails.com/products/onedesign/cni.asp?NID=11&CID=5 - http://www.quantumsails.com/products/onedesign/cni.asp?NID=1 1&CID=5 Mark Reynolds gen on it. Also have a look at http://www.stargear.net/articles/torbenjibe.html - http://www.stargear.net/articles/torbenjibe.html for how the top guys gybe with the rig forward and the crew on the foredeck. As for high performance boats - i'll bet there's not a lot quicker than the Star in the light stuff dead downwind, and until the apparent comes up enough for a boat to plane the fundamentals still apply. Stars plane too you know! Yes - the masts are fragile, but that is the nature of the boat. It's pretty easy to sail with the rig back and the mast will be fairly safe[ excluding gear breakages etc]. But let it forward if you want to win. Likewise it would be dead easy to make a bigger heavier section with fixed spreaders that was really damage tolerant, but like all racing equipment you have to push the design limits to go faster and if you have ever seen a Star mast in the flesh you'll know just how much of a noodle it is. Keeping the rig in the boat is all part of the sailing stars. It might seem an odd boat to much of the UK but the worlds best sailors along with around 3000 active boats worldwide can't all be wrong! Bear in mind no-one has retained a Star Worlds in over 20 years, which does say something about the top level in the class.
Kenny - Star 7665
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Posted By: Stefan Lloyd
Date Posted: 04 Sep 06 at 12:59pm
Originally posted by Guest#260
No doubt it is fast as all the Star guys do it - I was just wondering if this translated to other classes - e.g. Taser or N12. |
Merlins will certainly knock off shroud tension downwind in order to both straighten the mast and rake it forwards. I can't speak for N12s or Tasers. Not sure if the latter have the control systems to make it work.
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Posted By: Stefan Lloyd
Date Posted: 04 Sep 06 at 1:05pm
For heaven's sake Kenny, if people who know what they are talking about butt in, it will ruin the whole forum.
Seriously, very interesting, thanks.
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Posted By: furtive
Date Posted: 04 Sep 06 at 1:20pm
If you look closely at the first pic in this thread, you can see the top telltale on the mainsail leech flying almost vertically (as we look at it). This would support the idea of getting air to flow up the sail by raking forward, and could also be used by the sailor to see if it's actually working.
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Posted By: far canal
Date Posted: 04 Sep 06 at 1:37pm
Posted By: Pierre
Date Posted: 04 Sep 06 at 1:46pm
Originally posted by Stefan Lloyd
For heaven's sake Kenny, if people who know what they are talking about butt in, it will ruin the whole forum.
Seriously, very interesting, thanks.
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Quite so Stefan. What is this forum coming to ?
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Posted By: CT249
Date Posted: 04 Sep 06 at 1:57pm
Thanks Kenny .
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Posted By: Prince Buster
Date Posted: 04 Sep 06 at 2:26pm
Originally posted by KennyR
It's all quite simple. It develops flow over the
main. If the mast is upright or raked back the rig can only develop
stalled 'drag' forces, but by raking the mast forward, the air can
escape upwards and thus develop flow across the sail. Bethwaite talks
about 'roll over vortexes' that work their way up the lee side of a
poled out jib, drawing air across it and helping to develop further
flow across the main. Personally we have found that when you get the
mast well forward and hoist the jib up, there is enough slack in the
forestay to start making the jib behave a bit like a spinnaker.
Either way it is waaay faster to have the rig forward than not. If
you look at the fundamentals of a Star rig, you can appreciate how
important this is. For a start the chainplates for the upper shrouds
are ahead of the mast, so that as the rig goes forward, the shrounds
loosen and the bend comes out of the mast. Also the mast heel is free
to move in Derlin or rollers, so that once the mast has hit the front
end of the mast gate, the heel can slide back 1"-2" for a bit more
forward rake. Thirdly the spreaders are free to swing forwards, so that
the leeward shorunds and spreaders do not cut into the main and spoil
the sail shape. It is generally best to have the rig max forward in
the light [helps keep the boom out too], so that the mast tip is almost
over the bow, with a slight inversion in the mast to develop am even
better flow and the crew lying on the deck as far forward as he can go
[hanging onto the forstay with one hand], and enough heel to keep the
tiller neutral. As the breeze comes on everything starts coming back
not only to keep the mast in the boat, but to make it controlable
[think laser with no kicker downwind]. Have a look at http://www.quantumsails.com/products/onedesign/cni.asp?NID=11&CID=5 - http://www.quantumsails.com/products/onedesign/cni.asp?NID=1 1&CID=5 Mark Reynolds gen on it. Also have a look at http://www.stargear.net/articles/torbenjibe.html - http://www.stargear.net/articles/torbenjibe.html for how the top guys gybe with the rig forward and the crew on the foredeck. As
for high performance boats - i'll bet there's not a lot quicker than
the Star in the light stuff dead downwind, and until the apparent comes
up enough for a boat to plane the fundamentals still apply. Stars plane
too you know! Yes - the masts are fragile, but that is the nature of
the boat. It's pretty easy to sail with the rig back and the mast will
be fairly safe[ excluding gear breakages etc]. But let it forward if
you want to win. Likewise it would be dead easy to make a bigger
heavier section with fixed spreaders that was really damage tolerant,
but like all racing equipment you have to push the design limits to go
faster and if you have ever seen a Star mast in the flesh you'll know
just how much of a noodle it is. Keeping the rig in the boat is all
part of the sailing stars. It might seem an odd boat to much of the UK
but the worlds best sailors along with around 3000 active boats
worldwide can't all be wrong! Bear in mind no-one has retained a Star
Worlds in over 20 years, which does say something about the top level
in the class.
Kenny - Star 7665 |
yeah, i go with what he said......
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Posted By: Skiffe
Date Posted: 04 Sep 06 at 2:55pm
It might be fast, but does it look good.
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