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Sail Panel Layout

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=13319
Printed Date: 16 Sep 19 at 12:24am
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Topic: Sail Panel Layout
Posted By: A2Z
Subject: Sail Panel Layout
Date Posted: 08 May 19 at 9:10am
Why do some boats have radial sails that radiate only from the clew all the way to the luff (e.g. Laser Radial, 9ers) whilst other radial sails have a panel running up the luff e.g. RS800, RS400? I imagine sails with a luff panel might cost slightly more and stretch less under downhaul load, but I can't imagine the 49er has compromised performance just to save a few pennies. Similarly, in the Solo class the North radial sail has a luff panel but the HD radial sail does not, and they are competing on performance not price. So, what's the thinking behind it?



Replies:
Posted By: mozzy
Date Posted: 08 May 19 at 10:25am
Depends how tolerant the cloth is of cross loading. Also depends on how much Cunningham ever gets pulled on versus kicker. 

I've always been surprised that the 9er don't run a full length luff panel. But then they use the same material throughout. The 800/400 has clearer panels lower down which you wouldn't want to be cross loading with downhaul. But then the 200 is all the same material and still has the full length luff panel...

If you look at the 29er (or 49er) they have the double cuff at the bottom which spreads downhaul loads, then the radial cuts below the second batten have extra reinforcing near the luff. Also the 49er generally have a lot more taping around the battens and the luff in general. 



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RS800 1144


Posted By: A2Z
Date Posted: 08 May 19 at 11:26am
Thanks Mozzy. It hadnít occurred to me the reinforcement on the 29er was for that.


Posted By: Sam.Spoons
Date Posted: 08 May 19 at 12:07pm
I'm not sure why radial cut sails are so popular with laminate sailcloths but with dacron the cloth is much more stretchy on the bias so aligning it to get just the right amount of stretch makes sense.

Perfectly good sails can be made using broad seam construction too but we'd need a sailmaker to chip in to explain the detail.


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: mozzy
Date Posted: 08 May 19 at 12:41pm
Laminate sails are made with directional bias due to fibre lay up, so even more so than Dacron they will benefit from proper orientation with sail loads which radial cut allows. Like Sam says,Dacron does hold tension better across it's fill, hence cross cut sails, but most of the benefit for radial in Dacron is in the seams.

Here in the 9er material you can see black which lines up with predominate load direction and a blue cross weave for stability. 


The obvious exclusion is those bespoke 3DL type sails, where you can make whole sails with correct fibre orientation and shape with no seams. 




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RS800 1144


Posted By: Sam.Spoons
Date Posted: 08 May 19 at 1:12pm
Yeah, thanks, as a Demon Design user in my Raceboard days I was aware of that but decided it would complicate the issue in my reply. Laminates are much more stable than woven sailcloth when stressed on the bias or across the line of reinforcement so I would have thought the gains would be much less significant. Demon race sails had a deliberately stretchy luff panel to allow extreme shape changes from huge camber to almost completely flat with a twisted off 'floppy' head. This allowed a single sail to work in 3-30 knots.

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: iGRF
Date Posted: 08 May 19 at 1:51pm
The Original reason for radial panels was to follow catenary load lines (look it up I'm not going to explain it) the inclusion of a vertical panel follows the foot to head load line and is preferred if there is going to be big downhaul tensions which there are obviously in windsurfing sails within which this was a popular feature once upon a time.

Now depending on where the sailmakers put their shaping, in the luff like windsurfing or panels as was the case i dinghies I presume still is, then there will be an element of both. I.e. the vert panel will be shaped at the luff and the radial panels will have some seam shaping, but not too great or it'll defeat the previous objective of locking the shape in place via the catenary stress lines.


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Posted By: mozzy
Date Posted: 08 May 19 at 1:57pm
Sam, I'm not so sure. Laminate tend to be made lighter than their dacron equivalents rather than stronger. 

I agree that Dacron when pulled diagonally will stretch more then laminate. But after some wear I've seen quite a few laminate sails just pull apart parallel to the main fibre direction. I think if you got the wrong loading you'd see some very short laminate sail lives. Which leads me to believe that getting the cloth orientated correctly for laminate is more important. 

Obviously there are a whole heap of fibre layups under the term laminte. If you take the old 200 sail that had lots of cross runs and was very thick. It behaved more like dacron and hence was fine with the cross cut. But most the new laminates (9ers and RS) have a much less dense weave.


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RS800 1144


Posted By: Sam.Spoons
Date Posted: 08 May 19 at 2:34pm
Yes, got you. My understanding is that the difference with dacron is that it stretches a lot more diagonally than in line with the threads, and more in line with the weft than the warp, inevitable 'cos of how it's made. the filler/coating reduces this (and that is one reason why old sails perform badly). Laminate sailcloth is inherently less stretchy than dacron and can be made with very little stretch in chosen directions (some stretch is necessary or the sail would only set correctly at one precise setting and be, effectively, non-adjustable). 

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: A2Z
Date Posted: 08 May 19 at 2:42pm
So the 49er doesn't have a luff panel because the cuff and seam tape reinforcement is enough to take the (presumably very high) downhaul loads?

Can the cuff really be credited with being able to do away with the luff panel, otherwise why do so many lower performance, less loaded, sails have a luff panel?

Edit: Just noticed the 49er FX does have a luff panel...


Posted By: mozzy
Date Posted: 08 May 19 at 3:08pm
Is that not an urban myth? At the top end there seems to be a constant drive for low stretch and they can still change sail shape through mast curve and clew tension. The only downside to low stretch seems to be durability.  Just because it's zero stretch doesn't mean it's a ridged 3D shape. 

Are sail-makers not pedalling that line that a bit of stretch aids performance because it sells more sails? Whereas the truth is the stretchy material is cheaper, especially in low volume, easier to work with and they can't be dealing with the inevitable warranty returns after people crease their ultra brittle fibre sails? 


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https://www.youtube.com/user/656mozzy/" rel="nofollow - YouTube Channel
RS800 1144


Posted By: mozzy
Date Posted: 08 May 19 at 3:39pm
Originally posted by A2Z

Edit: Just noticed the 49er FX does have a luff panel...
But are made by North... North and hyde seem to like that luff panel.

Having said that, North also did the 29er and 49er before they went to neil pryde and the 29er always had the same panel pattern with radial all out from the clew. 

I do think the double luff cuff thing makes a difference though. It really spreads that downhaul load. There's no sail eye to concentrate loads... yet the 49ers did have reported issues with Cunningham loads on the sails, I'm not sure what was done to fix that.  

I reckon by the time you've either done a double cuff and put extra reinforcing on the lower panels near the luff then doing away with he luff panel is certainly no cheap option. 

The HD Solo radial cut does have more reinforcement panels for the down-haul compared to Norths Radial Solo or HDs cross cut which is using a special laminate. 

I'm not surprised HD think the cross cut is fastest. I reckon it's easier to make subtle sail shape changes to in the panel cutting and without the extra seams the sail is less stiff so sits nicer.

p.s. £920 for a solo main, £100 more than my RS800! 


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RS800 1144


Posted By: davidyacht
Date Posted: 08 May 19 at 3:49pm
My North P2 Solo sail cost £726 earlier this year ... using Northís seasonal discounts.

There is a good explanation of the HD cross cut sail here ...

http://www.hdsails.com/home/golden-solo-sail/" rel="nofollow - http://www.hdsails.com/home/golden-solo-sail/

But I think that the reason for the crosscut is that HD wanted to use the gold fabric as is derigeur with some Finn sails, which required this, and has been used to great effect by Taxi.

I think that the ultimate Solo sail would be one that is super stable when it is breezy, but light and flexible to be easy to read in light winds ... 


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Happily living in the past


Posted By: craiggo
Date Posted: 08 May 19 at 5:04pm
My understanding of the luff panel is to allow large changes of mast bend to be accommodated without unduly affecting the shape of the main panels.

Take for instance an RS300 which has a very soft mast which with kicker and cunningham released will stand pretty vertically for downwind and light winds sailing but for heavy airs upwind will have significant bend.
A traditional sail would not cope well with these extremes however the large stretchy luff panel enables a good sail shape at both extremes.

If you take the 49er, while the rig has a lot of bend in it, that bend is pretty well locked in, so the sail can be designed and cut for the bend. This makes them an arse to hoist.

I can't see much need for it on a Solo but some of the softer rigs may benefit from it.

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OK 2071 & 2129
RS200 411


Posted By: giraffe
Date Posted: 08 May 19 at 7:04pm
I donít think that most customers are sufficiently competent to use a radial sail. Cross cut is much more user friendly


Posted By: mozzy
Date Posted: 08 May 19 at 9:20pm
Originally posted by craiggo

My understanding of the luff panel is to allow large changes of mast bend to be accommodated without unduly affecting the shape of the main panels.
But surely the point of inducing mast bend is to affect the shape of the main panels? 

Originally posted by craiggo

Take for instance an RS300 which has a very soft mast which with kicker and cunningham released will stand pretty vertically for downwind and light winds sailing but for heavy airs upwind will have significant bend.
But, isn't the point of those two extreme mast curves supposed to pull depth out, or push depth into the sail, to either reduce drag or increase power?

These luff panels are made out of the same cloth, just orientated differently, so I'm not sure hey will be adding lots of stretch.  

Originally posted by craiggo


If you take the 49er, while the rig has a lot of bend in it, that bend is pretty well locked in, so the sail can be designed and cut for the bend. This makes them an arse to hoist.

The 49er does run a lot of mast curve, but I don't think it's at all locked in. Sail controls will change mast bend significantly. 


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https://www.youtube.com/user/656mozzy/" rel="nofollow - YouTube Channel
RS800 1144


Posted By: Steve411
Date Posted: 08 May 19 at 11:31pm
These luff panels are made out of the same cloth, just orientated differently, so I'm not sure hey will be adding lots of stretch.

In the 300 sail the luff panel is made out of dacron and the remainder of the sail out of laminate exactly so that extreme mast bend can be accommodated.


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Steve B
RS300 411
D-Zero 11

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Posted By: rich96
Date Posted: 09 May 19 at 3:58am
The Finn sails don't use a luff panel (some are cross cut and some radial) ?


Posted By: A2Z
Date Posted: 09 May 19 at 5:39am
The radial Finn sails I have seen donít radiate all the way from the clew to the luff, they do do have a vertical luff panel.  Tri-radial, is that the term? 


Posted By: Paramedic
Date Posted: 09 May 19 at 6:07am
Originally posted by giraffe

I donít think that most customers are sufficiently competent to use a radial sail. Cross cut is much more user friendly

I'd agree with that on the basis I have yet to use a fully radial sail I've liked.


Posted By: rodney
Date Posted: 09 May 19 at 8:01am
When it comes to Finn sails my preference is always radial regardless of conditions.  I have both but the cross cut sail stays in storage and is, probably, soon for sale.  Having said that I've been using radial Finns sails for a very long time so it may be just that I am comfortable with them?

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Rodney Cobb
Suntouched Sailboats Limited
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rodney@suntouched.co.uk


Posted By: Sam.Spoons
Date Posted: 09 May 19 at 12:01pm
Originally posted by mozzy

Is that not an urban myth? At the top end there seems to be a constant drive for low stretch and they can still change sail shape through mast curve and clew tension. The only downside to low stretch seems to be durability.  Just because it's zero stretch doesn't mean it's a ridged 3D shape. 

Are sail-makers not pedalling that line that a bit of stretch aids performance because it sells more sails? Whereas the truth is the stretchy material is cheaper, especially in low volume, easier to work with and they can't be dealing with the inevitable warranty returns after people crease their ultra brittle fibre sails? 

I can't see that (well maybe they are trying to big up cheaper materials), but a non stretch sail would only set one way and any changes would introduce creases. In fact, most laminate sails do have creases much of the time which I attribute to the fact that they don't stretch much. Sean Cox (Demon Sails designer) always said that small creases didn't affect performance as they were within the boundary layer, I suspect he is well qualified to comment as his day job was designing fighter plane wings.

My Hyde replica sail looks awful down wind in the light stuff but seems to go well enough. Once you get some pressure the mast bends and it looks fine. The Blaze M7 mast is pretty stiff though so that doesn't help. 


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: mozzy
Date Posted: 09 May 19 at 1:28pm
Originally posted by Sam.Spoons

a non stretch sail would only set one way and any changes would introduce creases. 

Well, you say that, but I don't believe it's true. Low stretch is tensile strength with low plastic deformation under tension.    

A sail that was very stiff would only hold one shape and would either crease (plastic deformation) or break (brittle) if you tried to change it's shape. 

Dyneema rope is very low stretch, lower than wire for the weight. But it's much less stiff. 

Dyneema / kevlar / carbon /polyester can all be used in laminate to reduce stretch, they won't mean the sail is stiff though. They can be made stiff if woven correctly in a resin however. In fact, almost all the stiffness in laminate sails is from the laminate, not the low stretch fibre. 

Sails that are very stiff are hard to set because they take quite a bit of force to deform. So you can't see your luff collapsing. They are also difficult to set in to different shapes without quite a bit of force from the wind, so again not good in the light. If you had a sail that was extremely stiff it would effectively be a hard shell and you wouldn't be able to tack let alone change it's shape. 

But low stretch does not equal stiff. 


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RS800 1144


Posted By: Oatsandbeans
Date Posted: 09 May 19 at 1:44pm
Sorry but low stretch does equal stiff- my day job is testing materials!


Posted By: mozzy
Date Posted: 09 May 19 at 1:55pm
Well illuminate us!

How can dyneema rope have the same tensile strength as steel rod (or wire), but then bend around a pulley without deforming? Why will a steel rod the same tensile strength as Dyneema stand up on end due to stiffness but dyneema rope won't? 


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RS800 1144


Posted By: Sam.Spoons
Date Posted: 09 May 19 at 2:29pm
If you could make a steel wire with the same number and diameter of fibres as dyneema rope it would be very flexible. If you take a metre of 2.5mm 7x19 wire you'll struggle to stand it on end, but it'll bend around your halyard sheave quite easily. 

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: Oatsandbeans
Date Posted: 09 May 19 at 3:51pm
Yes. The reason that high stiffness fibres can bend round sheaves is that they are made from filaments typically 10 microns in diammeter.


Posted By: Sam.Spoons
Date Posted: 09 May 19 at 3:58pm
My experience of this came from braided copper electrical cables.

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: mozzy
Date Posted: 09 May 19 at 9:15pm
I still feel the stiffness of the cloth is more related to the thickness or weight than the stretch. 

I can't imagine a low stretch sail creasing up when you pull depth out. 


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RS800 1144


Posted By: Oatsandbeans
Date Posted: 09 May 19 at 9:30pm
You may be getting confused with the stiffness of the cloth to bending , you can guage this with bening it in your fingers which is very thickness dependant, and the stiffness to tensiles loads( which is difficult to assess unless you have the kit), it is its resistance to temsile loads whcih is what the sail makers are interested in. Interestingly the latest sails ( North 3 di) appear to have extremely high in plane stiffness. They don't need to be pulled about ( and can't be) like a more flexible sail but they hold their design shape despite changes in the wind loading due to their amazing stiffness properties ( I am not an expert on sailcloth but it looks like that to me)


Posted By: A2Z
Date Posted: 09 May 19 at 9:33pm
I think this discussion is at cross purposes.  Mozzy is taking about a stiff sail as in one that doesnít flap/flog, and a low stretch sail as one where the fibres/panels donít elongate under tensile load.  Different planes. 


Posted By: Sam.Spoons
Date Posted: 09 May 19 at 9:36pm
Yes, I fear that is the case.

I still believe that a change of shape relies on stretch to keep it smooth, if the sail had no stretch changing it's shape must induce creases in one direction or another. I can't think of a way to explain but I can't see how it can be otherwise.


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: iGRF
Date Posted: 09 May 19 at 9:43pm
I think your getting too tied up in the detail and forgetting what the holy grail of sailmaking was all about.

The idea of the perfect shape that held, resisting the wind force to shift the flow point beyond the correct design parameter is always the goal, yet with the ability for some on the fly correction or auto correction for gust response without losing drive and to do that a sail built with cloth that doesn't arbitrarily shift or stretch about is obviously the best outcome.

The best example I ever came across was Cuben Fibre which was a multi directional random scatter fibre laminate, I've still got it thirteen years on and it works well, think they went on to create a waft and weave look because it wasn't generally adopted, it was quite expensive, but light, stiff, low stretch, it had it all, got a picture somewhere maybe I'll tag it on later.



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Posted By: davidyacht
Date Posted: 10 May 19 at 7:06am
The quest of the best sail is the ultimate compromise ... the ability to have gust response, stability, light weight, fullness to punch through waves, flat for low drag, a plethora of different materials, different mast bends, price, fashion and the personality of the sailmaker have been a constant drain on my wallet for forty years

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Happily living in the past


Posted By: Sam.Spoons
Date Posted: 10 May 19 at 9:59am
ClapClapClap



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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: SoggyBadger
Date Posted: 10 May 19 at 9:25pm
Originally posted by Sam.Spoons

Yes, I fear that is the case.

I still believe that a change of shape relies on stretch to keep it smooth, if the sail had no stretch changing it's shape must induce creases in one direction or another. I can't think of a way to explain but I can't see how it can be otherwise.


It rather depends on how the panels are laid out. On a cross-cut sail the cloth will naturally fall into a smooth shape even using laminates. Radial cut sails generally have enough panels in them that the curve closely approximates a smooth curve. The vertical wrinkles you often get at the luff of a laminated main don't matter as they're going with the air flow not across it.


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Best wishes from deep in the woods

SB



Posted By: Sam.Spoons
Date Posted: 10 May 19 at 9:47pm
Originally posted by SoggyBadger

Originally posted by Sam.Spoons

Yes, I fear that is the case.

I still believe that a change of shape relies on stretch to keep it smooth, if the sail had no stretch changing it's shape must induce creases in one direction or another. I can't think of a way to explain but I can't see how it can be otherwise.


It rather depends on how the panels are laid out. On a cross-cut sail the cloth will naturally fall into a smooth shape even using laminates. Radial cut sails generally have enough panels in them that the curve closely approximates a smooth curve. The vertical wrinkles you often get at the luff of a laminated main don't matter as they're going with the air flow not across it.

Surely the flow across the sail is mostly horizontal (that's what my teltails tell me) so a vertical creases is across the flow?

It's no problem getting a sail to have a smooth shape under a specific tension on a specific mast like bending a piece of flat metal sheet into a shallow bowl shape. But the metal will only bend in one direction at a time, to get a 3D curve you must stretch the metal in some places (done with seam shaping on a conventional sail and by heat moulding on a 3DL). In the case of metal it then retains that shape but we need sails to change shape and then return so, to achieve that, stretch must remain within the elastic limit. 

I'm sorry I can't seem to explain this clearly but, to me, it's obvious..........


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: Oatsandbeans
Date Posted: 12 May 19 at 9:42am
It is interesting Davidyacht. That is definitley very sensible to have a compromise and use a rig that is good at everything.
, but if someone gave me the choice of two rigs -one a perfect compromise that would be competitive in all conditions or another that was a complete "rocket" in the conditions that we most race in and a bit tricky in some conditions ( that posibly may require me to adjust my technique -and learn how to deal with it) i would go for the " rocket" every time.


Posted By: davidyacht
Date Posted: 12 May 19 at 3:16pm
Which is why I have a dacron sail for light winds tucked away ...

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Happily living in the past


Posted By: Oatsandbeans
Date Posted: 12 May 19 at 4:05pm
Exactly!


Posted By: SoggyBadger
Date Posted: 12 May 19 at 7:04pm
Originally posted by Sam.Spoons


Surely the flow across the sail is mostly horizontal (that's what my teltails tell me) so a vertical creases is across the flow?


And your tell-tails are telling the truth. I'm rather confused about where you think this vertical crease comes from though? I've not seen one of those which was causes by anything other than too much Cunningham or luff tension, neither of which is related to the sail's panel layout.


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Best wishes from deep in the woods

SB



Posted By: Sam.Spoons
Date Posted: 12 May 19 at 10:23pm
Sorry, clearly cross purposes, I was referring to the vertical wrinkles you mentioned. I agree that wrinkles (as opposed to 'creases' though that was the term Sean Cox used) do fall within the boundary layer and don't affect performance.

I believe creases/wrinkles are common when a sail is tensioned beyond (or below) its design limits and the limits of adjustment are exceeded. Sailcloth with more stretch will accommodate a wider range of adjustment/shape but will hold it's shape less well under load and will have sub standard high wind performance. A low stretch cloth will make a sail which keeps it's shape better under load but will have less range of adjustment and be 'stiffer' and harder to read in light winds. Under load the aim is to allow gust response but keep the CoE reasonably constant so the sail spills in the gusts without unduly moving the CoE. Floppy head designs in windsurfing which set on downhaul alone are a perfect example but they tend to be slow in lighter winds. Dinghies have and significantly more sophisticated rig controls so can cope with a wider range of wind speeds with a single sail so the dinghy equivalent is a bendy mast and lots of cunningham.


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"



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