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PostPosted: Sun Oct 14, 2012 8:38 pm 
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This screenshot from my Lowrance Elite4 shows the tacking angles I was able to achieve offshore yesterday. Winds were strong enough for the sail to be furled to the first batten, and the surface was choppy. But for all that, these tacking angles seem consistent with those obtainable in inland sailing (when not influenced by tidal flows.)
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PostPosted: Mon Oct 15, 2012 12:10 pm 
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Well, you did sail upwind.

You know gentlemen don't do that, right? ;)


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PostPosted: Tue Oct 16, 2012 7:57 am 
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Here is our track on Google Earth as we tacked into the wind on the 8th day of our Chok-FLM trip last January. Both of our AIs seem to be sailing closer to the wind than your TI track indicates--my wife, the blue tack, is doing better than I am. I don't know the reason for the apparent difference with your tack. We were tacking into about 13 mph (11.3 kt) winds.

Image

Keith

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PostPosted: Tue Oct 16, 2012 10:08 am 
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That is amazing Keith, as you are both tacking through angles less than 90 degrees, which is better than pure racing keelboats like Etchells 22s can achieve. The only possible explanation I can think of is a solid tidal flow from left to right.

I would really love to see more tracks shown by you and others, as I cannot believe that my own tacking angles (based on many screenshots) are due to poor sailing or equipment.

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PostPosted: Tue Oct 16, 2012 5:29 pm 
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Hi Tony,

We did have a favorable tidal flow, but it was just a 4' tide change. We left at mid-tide to gain the best flow. On the other hand, we traveled relatively close to land, not out in the main channel where the current would be greatest. It is just a guess, but I don't think the current was that helpful, it just was not against us.

So, I guess we will just have to put the difference between your and our tracks down to equipment and/or skill. Now, I have NEVER claimed to be a good sailor (I'm a kayaker, or I used to be); nor has anyone ever said I was a good sailor--notice, even my wife, who sails less than I do, is sailing a slightly better tack than I am (however, I did land at FLM ahead of her.)

So, it comes down to equipment, and, perhaps boat weight--we were still carrying a lot of equipment from our week-long camping trip. One more item that certainly makes a difference is that I motor sail, i.e., I pedal most of the time, which allows sailing closer to the wind (but my wife does not, which, looking at our tacks, again proves that she is a better sailor than I am.) I have to motor sail in order to keep up with all my friends.

Keith

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I sail: Biscayne Bay, Everglades to Cape Romano, Ft Desoto, Cedar Key

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein


Last edited by Chekika on Wed Oct 17, 2012 1:50 pm, edited 1 time in total.

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PostPosted: Wed Oct 17, 2012 12:43 am 
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The rules about tacking get turned on their head when the Mirage drive comes into play. In lighter winds (~5 knots), you can pedal just a few degrees off the wind and still get assistance from the wind. I think it should rightly be described as "pedal-tacking". Fusioneng has noted this effect too. As the wind get stronger, the drive contributes relatively less and the angle at which you can tack gets wider and wider. By the time you get to 30 knots, the best an AI can do is about 85° to the wind.

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PostPosted: Wed Oct 17, 2012 12:50 am 
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Keith, your wife might just be better at sailing upwind than you are, but I noticed something:

Quote:
Red '09 AI (Nancy's); dune '11 AI with vertical rudder


I wonder whether the "better" rudder is actually creating more drag. That could be the fault of rudder or operator, or it could be that you would do even worse with an old style rudder.


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PostPosted: Wed Oct 17, 2012 1:16 am 
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I would like to see GPS trails showing Islands consistently outpointing pedigree racing yachts like Etchells 22s or even America's Cup 12 metre yachts. I have no doubt at all that pedal-sailing in light winds can throw the rules out, but frankly, 85 degree tacking angles at 30 knots are literally incredible for an Island. I would love to be corrected of course.

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PostPosted: Wed Oct 17, 2012 6:02 am 
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Maybe there's something wrong with my terminology Tony. If a boat can't do less than 90° to the wind, it can't tack at all. So what's so incredible about an AI tacking at about 85°?

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PostPosted: Wed Oct 17, 2012 11:57 am 
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This thread surprises me a little bit. Perhaps I'm overlooking something. I have a good compass mounted on my AI and spend a great deal of time on the water watching it. Taking as best care as I can to determine wind direction and course, I can routinely travel at 50 degrees to the oncoming wind direction. Many times, just for learning purposes, I go tighter and tighter just to see when things will fall apart. In almost every instance, once I go closer than about 47 or 48 degrees to the wind, I'm done. This is without any assistance from the Mirage Drive, of course, and we'd be talking about winds of anywhere from 12 to 18MPH.

Something I did the other day, which was again a learning session, was to put the bow directly into the wind, until the same amount of wind was passing over both sides of the sail. Then I'd take a reading of the wind direction and fall off until the sail took over and the AI began making headway. In almost every instance, at about 47 to 48 degrees to the wind direction, the AI would take off.

Working from a deck mounted compass and understanding that wind direction can easily shift a few degrees at any point at any time, I assume my numbers may be off a degree, or two, or three. But I think they're reasonably close. In fact, I feel pretty good about the AI's ability to run darn close to the wind. At least nearly as close as most of the other boats on the water with me. Then again, there may be a flaw in what I'm doing to get these numbers, but I'm not aware of it at the moment. I'll keep thinking on it.


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PostPosted: Wed Oct 17, 2012 12:27 pm 
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Chris and Tom, I think the issue is partly one of terminology. "Tacking angle" usually refers to the difference in diegrees (ie: included angle over the ground) between a port and starboard tack. This number will vary between 90 odd degrees for high performance racing yachts, out to 170-180 for old-time sailing ships. Our Islands are in between, at something like 110 degrees

Therefore, it does not take into consideration where the bow is pointing, or the angle to the apparent wind (the angle of which changes depending on the speed of the vessel). So we see an America's Cup yacht steering as close as 30 degrees to the apparent wind, while it is actually proceeding at 45 degrees to the true wind (ie: across the ground). So such a yacht would have a tacking angle of 90 degrees.

Tacking angle is also after allowing for leeway or tidal influence, which is the difference between the compass heading shown on a sailing vessel and the track it makes over the ground, so a strong tide will make quite a strong difference to the tacking angle.

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PostPosted: Wed Oct 17, 2012 2:15 pm 
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Very good. If we're talking about the difference between course on a port and a starboard tack, then I would be hard pressed to do less than 90 degrees. In fact, it would be a few degrees more than that at best.


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PostPosted: Wed Oct 17, 2012 9:49 pm 
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I guess I don't know my nautical terms as well as I should. In the past I have described sailing points off the wind. For example if I stop and get a fix on wind direction (direction it is coming from), I start pedaling then point the boat somewhere between 5 and 15 degrees from the wind, then pedal lightly as I'm sailing (I always pedal anyway). If I don't pedal my boat tends to want to head up straight into the wind and stop.
I suspect I can only sail this close to the wind because I have a jib sail, without the jib my upwind results would be no different than anyone elses. The setup I have all works fine in any winds 3-12mph.
CaptnChaos (jim) was out with me a couple weeks ago, and sailed almost directly into the wind (he was driving my boat), we had a good time.
In higher winds (>15+mph) I tend to point as high into the wind as possible with full sails out and pulled fairly tight (maybe 20-25 points off the wind). This is probably a little dangerous because with that much sail out I would surely turtle in higher broadside winds. As the winds pick up (like on a gusty day) I tend to round up into the wind higher watching my AMA's if they bury I point higher verses furling the sails, or releasing some sail control line out. I guess what I mean is the actual sailing direction (compass heading) is secondary to watching the sail and reacting to wind changes by changing direction slightly to keep the sail working efficiently.
My reasoning for pointing so high into the wind is I feel going in a near straight line at 4-5mph gets me where I want to go upwind faster than zig zagging and working like crazy.
I don't know about anyone else but when the winds are over 25mph, I have difficulty going upwind at all (even zig zagging with a furled sail). My modified TI was pretty much rigged for the low winds typical where I live (Florida), and doesn't do as well as a stock TI in very high winds, so I tend to stay home in those conditions.
Hope all this helps
Bob


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PostPosted: Wed Oct 17, 2012 10:54 pm 
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Great contribution Bob, it is all good for people learning more about sailing. A lot of the time, as I have to make heaps of tacks to avoid all the oyster leases here in Wallis Lake (half of the oysters sold to Sydney's 4 million population come from this lake), I pedal like crazy going through the tack, gaining ground directly upwind in lighter winds, and helping to keep speed during the tack in heavier winds. The GPS track shows this as rounded corners on the tacks as below. (I started tracking while heading right to left, downwind, while the windward track was some hours later. during my return, helped by some favourable tidal flow.
Image

However, I would love to see more GPS tracks posted here, as they show "real world" angles over the ground. Ideally tidal forces should be noted (eg. The entrance to the sea from this local lake sees tidal flows of up to NINE knots, so any GPS track from there would be confusing without knowing the tide. Yesterday I sailed out on a beam reach and was hitting a consistent 8.5 knots, but coming back in, (while surfing!) maximum speed was only 3.8 knots over the ground, and forward speed in the lulls was under one knot...

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PostPosted: Thu Oct 18, 2012 5:51 am 
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Which gets you there faster - a straighter course at a lower speed, or a higher speed but a less direct course? Isn't this a big part of what the sailing races are all about?


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