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PostPosted: Tue Oct 15, 2013 10:04 am 
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I'm new to sailing this year. I'm trying to figure out where my main sail traveler should be set for each point of sail.
I was going with a rule of thumb that it should be centered for closed hauled, about a 1/4 of the way out for close reach, half way out for a beam reach, and all the way out for a broad reach/run.

Then I went out with a guy who's been sailing for 20 years and is certified. He said instead of letting the traveler out, just keep it centered and let out the main sheet. Keep in mind this is a mono hull guy.


Can you guys chime in on this?


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PostPosted: Tue Oct 15, 2013 10:41 am 
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Go with what you are doing,his metode will not even work on a Monohaul.
Remember your settings are ballpark figures .Do not be afraid to fine tune with both traveller and main sheet.Nice to have a trial boat with you to compare speed.Not only important for speed to adjust but also to stay in control.
Remember in bigger winds not only is a flat sail faster it also helps you stay in control.Only way to keep a flat sail is with sheet tension and down haul.,that is why to keep sheet tension you will need to travel out.


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PostPosted: Tue Oct 15, 2013 10:48 am 
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1) What mmadge said. In general, the traveller will affect the lower telltale more, and the sheet will affect the upper more.

2) I highly recommend Rick White's Catamaran Racing for the 90's even for non-racers. The first chapters on sail trim and boat handling are invaluable.

3) You'll be smoking your certified friend soon!

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PostPosted: Tue Oct 15, 2013 10:58 am 
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mmadge wrote:
Remember in bigger winds not only is a flat sail faster it also helps you stay in control.Only way to keep a flat sail is with sheet tension and down haul.,that is why to keep sheet tension you will need to travel out.



This interests me and I don't understand it. I was in big wind last weekend and it was too much for me. It was over 20mph.

A flatter sail helps you stay in control?
and why do you have to have the traveler out to keep sheet tension? Couldn't you keep sheet tension while close hauled?


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PostPosted: Tue Oct 15, 2013 11:09 am 
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Lots of sail theory goes into this.Probably someone with more theory can explain better then I.
Here is my KISS approach.the more curved your sail the more power and drive it has.that is good in light to moderate wind with some lumpy water,then you want power and drive.In bigger winds the Hobie has more sail area and power then you need.to harness all that power you flatten the sail,down haul more travel out and sheet tight.Net result is sailing much more controlled.


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PostPosted: Tue Oct 15, 2013 11:45 am 
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nboyer941 wrote:
I'm new to sailing this year. I'm trying to figure out where my main sail traveler should be set for each point of sail.
I was going with a rule of thumb that it should be centered for closed hauled, about a 1/4 of the way out for close reach, half way out for a beam reach, and all the way out for a broad reach/run.

Then I went out with a guy who's been sailing for 20 years and is certified.


Can you guys chime in on this?


Or did you mean certifiable?


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PostPosted: Tue Oct 15, 2013 11:55 am 
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I don't know. I know he took classes overseas.


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PostPosted: Tue Oct 15, 2013 7:28 pm 
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Location: Perth - Western Australia
Had an interesting session with Gavin Colby on the weekend and traveller position was covered a fair bit.

He basically said he generally does not centre the traveller except if they are currently single trapeezing and he thinks maybe he might be able to get to double trapeezing by squeezing it on
Once comfortably double trapeezing the travellers goes out a few inches getting further and further out as pressure increases. Never go further then the footstrap otherwise you will have issues with the mast counter-rotating.

He suggested that if you are still overpowered at this point you would actually bring the traveller back closer to the centre and ease the main more. The boom stays roughly where it was but you will be more twist in the sail which will depower.

Downwind traveller all the way out and trim main. Did not really cover reaching much as we don't do a lot of it in our races :)


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PostPosted: Wed Oct 16, 2013 7:06 pm 
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I will try to explain in only a few words why you want a flatter sail in higher winds. It does not necessarily depower the boat. In light air you want a thick wing like on a slow flying heavy lifting airplane (crop dusters). You want as much lift as possible. The slower moving air will be able to stay attached to the sail/wing even over a very curved surface. As airspeed increases the air will separate (stall) with the deeper sail curvature (thicker wing) unless you flatten the sail to reduce the curvature (decrease angle of attack for an airplane). Keeping this in mind, as airspeed increases and the sail curvature is kept constant, more lift (power) is created as long as the sail does not stall. Also, for the same airspeed assuming neither sail will stall, a flatter sail will produce less power. If you are at an airshow, look at the utility aircraft wings and compare them to the high performance fighters or business jets. You will see that the faster the plane flies, typically the thinner the wing thickness is, relatively speaking.

In order to keep in control, you need to do something to reduce the amount of power the sail produces (flatten the sail or spill air by adding twist). To go fast, you want as much power as possible to drive the boat forward. If you are heeling too far over, you are not only spilling air off the sail but you are now loosing energy maintaining the angle of heel (I think flying a hull up high is fun so sometimes I do this on purpose) instead of driving the boat forward. For max speed in any wind condition on a cat you want the windward hull just kissing the water. On a monohull, neglecting CCA hull designs (long overhangs), you want to be as flat as possible.

To address the 20 year sailing veteran's comment on traveler position; many smaller monohulls are not wide enough to take any significant advantage of traveler position unless you are really dialed in.

I hope this helps and did not ramble too much.

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'84 H16
'82 H18 Magnum
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PostPosted: Wed Oct 16, 2013 9:43 pm 
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Brilliant. Thanks Nick.

And now can you explain the absurdity of apparent wind directions on a downwind hydrofoil? :wink:


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PostPosted: Thu Oct 17, 2013 10:29 am 
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I think a lot of your confusion here is due to the fact that "flatter" is being used to describe different parts of sail shape: depth, angle of attack and twist.

Depth:
how much "shape" the sail has. this is the thick vs thin wing that Nick described so well- thicker wing (more depth)=more power, thin wing (less depth)=less power. you can see how much depth the sail has by imagining a straight line from the front edge of a batten to the back edge; how far off the actual sail is from that imaginary straight line is is the depth. Your primary controls for this are downhaul, outhaul (not as effective as the other two) and mainsheet. when you tighten any of these controls, they stretch out the sailcloth and bend the mast, which gives you less depth in the sail and therefore less power. this is what MMadge meant when she said a flatter sail keeps you in control better.

Angle of Attack:
This is the angle that the sail makes with the wind direction:
Image
Up to a point, higher angles of attack (bigger difference between the wind direction and where your sail is pointed), give you more power. However, beyond a certain point, the sail stalls and gives you no power and a lot of drag. Too low of an angle of attack and the sail just faces into the wind and doesn't produce power. This is controlled by the combination of sheet tension (see "twist") and traveller position for a given sheet tension, having the traveller towards the center of the boat increases the angle of attack and the amount of power).

Twist:
If you imagine looking down on the boat from above while sailing upwind, the sail isn't all going to be pointed in the exact same direction. the boom will be closer to the centerline of the boat than the upper part of the sail, which will be falling off to leeward. The angle between the two is the "twist" in the sail. its controlled by the tension of the sheet. in higher winds, there is more force trying to push the top of the sail to leeward, so you need more mainsheet tension to maintain the same amount of twist. the correct amount of twist will give you the "optimum" angle of attack for the sail from the boom all the way up to the top of the mast.

Putting it all together:
in light to moderate conditions, where you're not overpowered (tipping too much), you want the traveller on centerline and sheet moderately tight (to keep the optimum amount of twist in the sail). If you're temporarily overpowered in a gust, you can ease the sheet, which will allow the top of the sail to twist off more, reducing the angle of attack towards the top and producing less power. when the gust is past, you can bring the sheet back in to power the top of teh sail back up.

However, as the wind builds for longer periods, you want to depower by decreasing the depth of the sail. dropping the traveller will reduce the angle of attack of the whole sail, depowering it, and allow you to carry more sheet tension without stalling the top part of the sail.

Off the wind the same basic principles apply, but you let the traveller out much further so you can sheet in some and decrease the amount of twist in the top of the sail.

Clear as mud, right?? The best way to see all of thise is to go out with someone who really knows Hobie Cats, and can drive while making various adjustments so you can watch the effect they have.


As for your friend's "certification", I've generally found that they aren't necessarilly worth anything. I know some really good sailors who have no formal training, and some terrible sailors who are "certified".

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PostPosted: Thu Oct 17, 2013 10:37 am 
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NOHUHU wrote:
Brilliant. Thanks Nick.

And now can you explain the absurdity of apparent wind directions on a downwind hydrofoil? :wink:


That one's easy. On a windy day, drive down a highway that the wind is blowing across. Stick your hand out the window and notice where it feels like the wind is coming from- in front of the car. It's because the car is moving so fast that the "wind" it creates overpowers the actual "true wind" that you would feel if stationary, so it feels like the wind is coming from more or less in front of you. Apparent wind on a boat is exactly the same thing:
Image
the hydrofoiling AC72's just go so fast that the boat speed component is huge. This means that the apparent wind is always in front of them, and so it looks like the sails are always trimmed for "upwind". Iceboats have been experiencing this exact same phenomenon for years

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PostPosted: Thu Oct 17, 2013 1:51 pm 
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Ahhh.... Apparent Wind, what an interesting subject.

This past weekend, (Canadian Thanksgiving Monday), we put this to good use on my 1989 SX18, with Tiger spin. Turkey Trot is the final race of the season, open to all. Boats are handicapped, slowest start first, fastest last. The course is a circle, about 2 miles in diameter, on the Ottawa River, here in the Nation's capital. Staggered start, twice around the circle, back to the start. NW Wind 9 knots gusting 15, light chop, air temps around 65F, sunny, and great sailing.

There were no dinghies, only keelboats, my SX18 and a Tornado. I was lucky to get Christian as crew. He is one of the top 505 sailors in Canada, and really knows how to run a spin. Mike Madge's lessons from August also helped. Thanks guys! We ended up 2nd, beaten only by Matt & Benoit on the Tornado, and we were a close 7 minutes behind them. I have never sailed so fast for such an extended period of time.... it was wonderful. Yes, my prize was a turkey.

There is nothing like smoking a bunch of 30' keelboats on the downwind legs, we flew by all of them.
On the 2nd leg, while scalloping to pick up apparent wind, one particular gust drove the boat so hard, we took water up to the front cross bar. No, we did not swim, as the advantage of the spin came through, lifting us up level again.

Seriously, Frank Bethwaite wrote a wonderful book, Higher Performance Sailing, or HPS, and a couple of years later, touched it up, and called that one HPS II. Thick, informative, interesting, expensive, and about 1,000 pages, with lots of technical diagrams, all explained in a simple way. See if your library has it before you shell out some big bucks. Read that, and you'll understand Apparent Wind, and what makes skiffs and cats go fast. Then go out there and have fun.

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'Only two things are infinite, the universe, and human stupidity. But I'm not sure about the former.'


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PostPosted: Fri Oct 18, 2013 9:32 pm 
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SNovak, I've been waiting to ask this and you seem like the right guy.

I sail in Hawaiian waters, (open water and sheltered) and we are blessed with big wind, 15-20 mph on the normal day. Often higher.

I've noticed a few high wind sailing videos where the skipper has the sheets locked and is using just the traveler to fly the hull for long periods of time. It seems to work great at spilling air smoothly while keeping the power zone. I wonder how many seasoned salts use this technique, and what they think of it.

Seems like it might be a good technique to use with out strong and gusty trade winds.


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PostPosted: Mon Oct 21, 2013 7:12 pm 
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NOHUHU wrote:
SNovak, I've been waiting to ask this and you seem like the right guy.

I sail in Hawaiian waters, (open water and sheltered) and we are blessed with big wind, 15-20 mph on the normal day. Often higher.

I've noticed a few high wind sailing videos where the skipper has the sheets locked and is using just the traveler to fly the hull for long periods of time. It seems to work great at spilling air smoothly while keeping the power zone. I wonder how many seasoned salts use this technique, and what they think of it.

Seems like it might be a good technique to use with out strong and gusty trade winds.

Honestly, someone like SRM or MBounds is probably a better bet to answer your question. While I have a lot of sailing/racing experience, the vast majority of it is in monohulls, so I can't comment as well on Hobie specific things like that.

My guess is that they're playing the traveler because it requires letting out and bringing in less line than the sheet, so they can power up and depower more quickly.

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