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DanWeiss
Joined: 24 Jun 2008
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Location: Connecticut, USA
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 Posted: Tue Jun 10, 2014 1:49 pm Post subject: |
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| QueNeo wrote: | It's not that cammed sails necessarily have a higher top end, it's that they get going faster and plane earlier out of jibes. If you're planning, you are faster than the guy who has more top end but doesn't get going till you are at the next mark. It's like a speed needle vs a modern wide slalom board - the speed needle will go faster, but it may not go at all until the other board is already at the first mark.
Once you have jibed, they already have shape. I just read online somewhere where Ben Severene wrote that one of his RAFs had a higher top end then his full on race sail.
They also should bring the COE forward.
Oh and it's another tuning point for racers, they can adjust cam tension which allows more control over where the COE is.
But there's other things in place too, when comparing race sails to non race sails, it's not just that they have cams, but more battens (8 or 9 on most) big luff sleeve, lower foot, and more twist. So they are different animals.
Really, wave sails and bump and jump haven't changed very much in a decade or even decade and a half, pretty much just reintroducing old styles, and new colors (more twist, less twist, more twist, more battens, less battens, etc) , while races sails are constantly changing, though in pretty small increments per year these days. The one recent trickle down from racing I can think of is the cut out clew, which brings COE forward also btw.
So, I would say for non race sails, ie 2 cam sails the main benefit if there is one would be earlier planing, and a more stable sail at the expense of maneuverability and weight. I also think rafs are not as mast dependent, since rotation isn't an issue. |
Some good thoughts! A few deserve a bit of further discussion.
Sure, there are a few RAF sails that could have a higher top speed than a race sail (non FW sized, of course) but I suspect that list is very, very small. If the list were larger, most amateur speed sailors would save a few dollars and go RAF. That said, we sail everything together and everything must match to get the fastest and most balanced performance possible. That's why matching rocker and volume flow means a lot when pairing sails to create a stable sailing experience.
Let's not confuse COE with entry angle or point of maximum depth. Sails often accelerate faster going upwind when the entry angle is more acute because airflow is less impeded. We see this effect when using an adjustable outhaul, pulling the OH brings the maximum depth forward and reduces the entry angle. Yet it also tightens the leech which pulls the COE back. Smaller race sails are designed mostly for slalom, where sailing angle is quite different. In this case, a rounder entry offers better flow attachment when the wind is very disrupted by others nearby and is more forgiving to changes in apparent wind angle. Yes, cams do create static shape after rotating but all those stiff battens work to take that shape out. That's why the foil is stable on a cam sail, because the cams work in concert with the seam shaping and battens to locate the draft and help keep it more in place. But I think that the cams do more to affect entry angle once a sail is full than actually and specifically locate the draft. In fact, the COE adds what's known as rotational lift (the force that causes the sail to spin around the mast foot) that allows us to have something to sheet against. Again, COE is related to draft placement and entry angle but is a different thing.
RAF sails are just as mast specific as if not more so than cam sails when thinking about shape and tension. RAF obviously cannot rely on cams to force shape and must primarily rely on the tension created by seam shaping and how it interacts with mast specs. Batten stiffness and bend curve also play a role, but batten tension works to keep a sail flat until the sail "fills" with wind. Racing sails usually rely on greater mast bend and luff tension to work well at all -even with adjustable cams, and have twist angles that are wider than most RAF sails, making the mast choices pretty strict. RAF sails without much luff curve are far less mast dependent. While performance characteristics of RAFs change when switching masts those changes can be "tuned" around, whereas a racing sail may limit its performance to one end of the range.
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isobars
Joined: 12 Dec 1999
Posts: 20935
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| Posted: Tue Jun 10, 2014 2:35 pm Post subject: |
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| QueNeo wrote: | | It's not that cammed sails necessarily have a higher top end, it's that they get going faster and plane earlier out of jibes. If you're planning, you are faster than the guy who has more top end but doesn't get going till you are at the next mark. |
Of course, the whole idea is to plane like Teflon-coated snot on wet ice, from reach to reach all the way through the jibes, with the sail unpowered (and thus unshaped in the case of an RAF) for just the second or so it takes to spin it. |
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Sailboarder
Joined: 10 Apr 2011
Posts: 656
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| Posted: Tue Jun 10, 2014 3:30 pm Post subject: |
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| DanWeiss wrote: | I'm sorry if my post covers old ground, but it's worth understanding that full-blown race sails work best on boards with rocker lines that contain some flat and trim out @ 4 degrees, more or less. One reasons race sails don't really work well on wave boards has everything to do with the incongruent forces.
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What "trim out @ 4 deg" means?
I tried a Kona One with RS:X 8.5 sail and felt the combo was great. Is that sail close to a full-blown race sail? I tought the cams had to be credited for the locked behavior. I also think the K1 has a flat part at the back, meaning it should behave correctly with a race sail? |
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QueNeo
Joined: 10 May 2014
Posts: 27
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| Posted: Tue Jun 10, 2014 4:39 pm Post subject: |
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| I'm trying to think of an example of accelerating faster upwind, and drawing a blank on that Dan (?) |
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GURGLETROUSERS
Joined: 30 Dec 2009
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| Posted: Tue Jun 10, 2014 4:54 pm Post subject: |
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Dan, your expertise with konas and sails is clear, so just to clarify a point.
I vary use between a 7.8 rotational (for play about mode) and a twin cam 8.0 set with only light twist for more serious upwind work. It has always been my impression from 80's longboard racing with large multi-cam pre twist sails that such definitely pointed higher (semi-planing, dagger halfish down) and held more speed and stability (i.e. carry) than a rotational sail.
Are you saying that cammed sails are now designed to work more efficiently with progessively larger degree of twist, than the older notion of less twist.?
What modern twin cam 8.0 would you suggest is the best match for the Kona, espewcially for protracted upwind beating, as on longish journeys? Are the Kona racing sails optimised just for such?
Thanks in advance. |
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techno900
Joined: 28 Mar 2001
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| Posted: Wed Jun 11, 2014 8:40 am Post subject: |
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gurgle said: | Quote: | | Are you saying that cammed sails are now designed to work more efficiently with progessively larger degree of twist, than the older notion of less twist.? |
Dan may give a better answer, but from my experience racing longboards from the mid 80's until I went to formula about 8 years ago, the old style race sails with cams and a tight leach with no twist were powerful. However they had much less range than the new race sails with lots of twist. There was a point where the COE moved way back with no way to manage it other than getting slammed.
Where I would have used a 8.4 on an old longboard in the 90's, I would likely rig a 9.2 for the same wind today. Similar pulling power at the low end, but able to handle stronger winds (greater range) because of the twist. Then add an adjustable outhaul and improve upwind and downwind efficiency and range. |
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DanWeiss
Joined: 24 Jun 2008
Posts: 2296
Location: Connecticut, USA
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| Posted: Wed Jun 11, 2014 1:22 pm Post subject: |
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| Sailboarder wrote: | | DanWeiss wrote: | I'm sorry if my post covers old ground, but it's worth understanding that full-blown race sails work best on boards with rocker lines that contain some flat and trim out @ 4 degrees, more or less. One reasons race sails don't really work well on wave boards has everything to do with the incongruent forces.
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What "trim out @ 4 deg" means?
I tried a Kona One with RS:X 8.5 sail and felt the combo was great. Is that sail close to a full-blown race sail? I tought the cams had to be credited for the locked behavior. I also think the K1 has a flat part at the back, meaning it should behave correctly with a race sail? |
Trim out @ 4 degrees is an ideal angle between the water and the board's planing surface. Maybe that number isn't perfect, but it was told to me by Randy French and Richard Greene at different times, so I take their word for it.
A wave board without any flat always rocks fore and aft more than a board with flat, like a slalom or FW board. That flat section is, among other reasons, why skilled windsurfers on slalom boards often appear to be pretty still. The board's with flat naturally settle at some angle (not always 4 degrees) and allow the sailor to keep the rig more or less at the same sweep angle. The pressure on the fin then can be more steady and the entire system gives more confidence at higher speeds than a wave board whose rocker is changing the board's drag coefficient all the time. That's the idea. I don't speak the gospel necessarily. Josh Angulo or others lurking may offer a very different idea.
The RS:X sail is close to but not entirely a full blown race sail, at least not in the convention of when it was designed. It is designed to be used with an adjustable downhaul as well as adjustable outhaul. PWA racing sails are not designed with that adjustability in mind. The twist in a current race sail tends to be more or less set to a smaller range using finite downhaul settings and is able to be modified on the fly only slightly using an adjustable outhaul.
Yes, the Kona One works fantastically well with certain racing sails, though in displacement mode a sail designed for PWA slalom racing or FW will not easily provide the range of the class-legal RAF sails because they incorporate more twist. I've sailed the Kona One with a different fin and a smaller FW sail: in that setting the FW sail worked better only when sailing the Kona One on the fin. The different fin and the class sail worked best in the broadest range. In each case, the board found it's "home" on its flat, but the FW simply was not efficient upwind or downwind in displacement mode. The Kona One is a one design with compromises made so it suits sailors of many skill and sizes. The Kona One rig offers terrific performance in any case, as anyone who attended the 2013 Midwinters can attest. Several of us paced the RS:X racers upwind and were pleasantly surprised that we could stay with them and sometimes beat them upwind when planing.
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DanWeiss
Joined: 24 Jun 2008
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Location: Connecticut, USA
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| Posted: Wed Jun 11, 2014 1:38 pm Post subject: |
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| QueNeo wrote: | | I'm trying to think of an example of accelerating faster upwind, and drawing a blank on that Dan (?) |
What I mean is that the air flow attaches at a lower wind speed and at angles close to the true wind when the foil is flatter and the entry lean. As the apparent wind builds, it remains critical to keep the entry lean so as not to stall the leading edge or create excess drag. Just think of holding your arm out the window of a car as it starts to roll. If your hand is shaped as a fist, it becomes unstable like a screwball. If your hand is more or less flat, it slices through the wind flowing around it (not cleanly, but more so than a fist) but also is more sensitive to changes in angle of attack. Sailing upwind on FW gear shows us that the apparent wind is more stable than if we sailed more slowly at a lower angle. Thus the lean-entry shape is far easier to control only because the apparent wind is pretty consistent upwind on FW gear. Once the force in the sail builds, we can sometimes ease the OH to create more power and gain some comfort with a slightly more open leach.
Contrast that to sailing downwind on FW gear. Then, the apparent wind angle changes wildly and rapidly when the board slows by hitting chop or sailing into a lull. By dumping the outhaul downwind, we create a more rounded entry angle that is more forgiving about variations in apparent wind just like sails designed for downwind slalom racing. We also allow the leach to twist off and that prevents both stall and the pitching moment that would occur as the apparent wind suddenly swings very far aft upon hitting a piece of chop.
So a sail will accelerate upwind better when lean if the apparent wind is forward and high, and the water fairly smooth. Once the water state or wind changes too far, the sail trim should change to offer greater flexibility -less balancing on a knife-edge.
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DanWeiss
Joined: 24 Jun 2008
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Location: Connecticut, USA
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| Posted: Wed Jun 11, 2014 1:59 pm Post subject: |
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| GURGLETROUSERS wrote: | Dan, your expertise with konas and sails is clear, so just to clarify a point.
I vary use between a 7.8 rotational (for play about mode) and a twin cam 8.0 set with only light twist for more serious upwind work. It has always been my impression from 80's longboard racing with large multi-cam pre twist sails that such definitely pointed higher (semi-planing, dagger halfish down) and held more speed and stability (i.e. carry) than a rotational sail.
Are you saying that cammed sails are now designed to work more efficiently with progessively larger degree of twist, than the older notion of less twist.?
What modern twin cam 8.0 would you suggest is the best match for the Kona, espewcially for protracted upwind beating, as on longish journeys? Are the Kona racing sails optimised just for such?
Thanks in advance. |
Gurgle, an average, modern (post 2006) twin-cam sail probably is a great match for the Kona or nearly any longboard for that matter because longboards require a lot of compromises in sail design to accept tuning changes that should occur across different conditions. Each sail is different, so it's no use applying a generalization to a specific example, but suffice to say that the Kona One sails are specifically designed for the Kona One and probably work better on the Kona One in racing situations than RAF sails not designed for the Kona One.
New vs. old cam sails: Yes, it's safe to say that a modern cam sail offers a superior wind range than those we sailed in the 1980s. I tested an old Gaastra Racefoil about 10 years ago, just to see what it actually felt like. I sailed it with carbon booms on a "high-performance" Serfiac alu mast -all tested and approved at top-drawer at that time. YUCK. The sail pulled like a truck but overpowered quickly. Again, this was a sail directly off the World Cup slalom series from around 1988, just prior to those early pre-twist designs.
I've always maintained that the sails could not progress much farther without a the breakthrough masts developed in the late 1990s. At that time, Fiberspar was at the cutting edge of mast design and manufacture. They released the Reflex 6000 which were the first production masts that allowed a lot of luff curve because they remained very stable, returning to a constant bend faster than anything available before. Sail designers then could create sails with a lot more internal tension yet which still felt soft in the hands. The sails before were fast, but only when wickedly powered up. So we were forced to use pretty large sails that performed well only going mach schnell. The newer sails rig on even better masts and now achieve that desired balance of performance without feeling on/off. Today, most every sail brand brings highly talented designers and terrific quality control that allows sails with large area to feel functional and comfortable across 15 knots.
So yes, modern cam sails are far superior in useful range than stuff from the mid-90s and earlier. But do we recommend using the same sail size to achieve the same performance upwind? No. That's the compromise.
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DanWeiss
Joined: 24 Jun 2008
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Location: Connecticut, USA
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| Posted: Wed Jun 11, 2014 2:10 pm Post subject: |
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Like most threads on iW, this has taken several turns from the topic of the OP.
With apologies, let me offer a final observation. Sails optimized for Raceboard Class performance longboard are sold, but not widely distributed in the USA. Tushingham and Sheldon are British brands with happy followers and winning designs. Loft Sails also sells a model called the Raceboard Blade.
Many other brands with better distribution in the USA offer twin or tri-cam sails tunable enough to drive longboards nicely upwind. The Aerotech Dagger is such a sail. The Sailworks Retro deserves mention, too, even though not a cam sail because the Retro is so very tunable. It's one of the best sail lines ever designed since it does nearly everything very well and is tailored for each size. Many USA sailors love the Ezzy Zephyr for no-cam performance, too.
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Last edited by DanWeiss on Thu Jun 12, 2014 3:22 am; edited 1 time in total |
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