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Negative rocker - paging Zirtaeb

 
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westadamsvets



Joined: 10 Aug 2006
Posts: 54

PostPosted: Fri Sep 07, 2012 2:11 pm    Post subject: Negative rocker - paging Zirtaeb Reply with quote

I recall some discussion a while back regarding slalom boards rocker lines becoming negative over time between the rear and front footstraps. The solution was re-fairing the rocker.

I also recall discussion regarding that new short slalom boards are somehow immune to this problem.

Bottom line - should I be taking a straight edge to the bottom of a well-used modern slalom board? Is this an issue - and has it ever been?

I figure LeeD - given his experience with slalom boards over the years, may have some insight...
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zirtaeb



Joined: 03 Jul 2009
Posts: 2281

PostPosted: Fri Sep 07, 2012 2:21 pm    Post subject: Reply with quote

Naturally, there are two sides to every story.
The technical guys would say having about 30" of dead flat from the tip of the tail thru the front straps, then a super gradual rise in rocker to the mast track, then more rise to clear the nose.
But reality is oftentimes a different animal. For some sailors, negative rocker, just a tiny amount, actually benefits both acceleration AND topspeeds, as the negative gives constant lift, while the rider can negate the negatives with a rider weight shift back.
Modern boards being newer, the jury is still out. But in theory, a shorter board that doesn't flex over time should retain it's rocker longer...but...the wider board will pound it's bottom at the mast track harder, causing the softspot to accelerate quicker.
All that said, most serious slalom sailors change their boards about 50 sailing days into their procurement, just like their fins and sails.
A not as sensitive non competitor like me, going only for top speeds and acceleration FOR FUN, don't matter, as I get my sail size choice wrong, my fin size choice wrong, and my board size wrong more often than not.
And the softer ride, coupled with softer fins, might allow more play and room for error so a easier ride, like freeride gear, might allow me to go just as fast as the newest slalom kits.
It matters more in your mind than you can possibly feel, unless you're making a living out of slalom sailing. I guess that's my final line.
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swchandler



Joined: 08 Nov 1993
Posts: 5687

PostPosted: Fri Sep 07, 2012 5:49 pm    Post subject: Reply with quote

Being that this is an interesting topic, I thought I would add to the discussion. In the transition from narrower boards with longer rockerlines to wider boards with shorter rockerlines, what I've noted is that newer designs tend to have a rougher ride. In saying this though, I have to admit to having experience with only one designer/builder, Mike Zajicek. Nevertheless, it does cover over 20 years of his slalom boards, so I think that some reasonable conclusions can be drawn overall.

What I've noticed over time is that the bottom of boards under the footstrap area get soft over time. While I don't think that leads to a real change in the rockerline, it does lead to a less crisp surface that might flex a bit more inside the outline of the board. Being that newer modern boards tend to ride a bit rougher, the softness under the footstrap area just might appear sooner.

If considering buying a used board, or deciding whether to buy a new replacement board, I would recommend using the coin test to discern the condition of the bottom. If you hold a quarter between your thumb and forefinger and then tap the board all over the bottom in the footstrap area, you can hear the areas that have become softer. The sound is dampened, and it just isn't real crisp and solid as it should be. To better understand the difference, try the test in the nose of the board forward of the mast track, as it usually always remains very solid and crisp over time, because it just doesn't take the beating the rear of the board does.
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zirtaeb



Joined: 03 Jul 2009
Posts: 2281

PostPosted: Fri Sep 07, 2012 5:53 pm    Post subject: Reply with quote

And IF you have your straps too far back, you will go faster with slight negative rocker. And IF you have the straps too far forwards, possibly a slight amount of positive rocker will allow you to go your fastest.
Fin size and rake of the sail has the same results.
It's not nearly science, but more art.
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nw30



Joined: 21 Dec 2008
Posts: 1538
Location: The eye of the universe, Cen. Cal. coast

PostPosted: Fri Sep 07, 2012 9:17 pm    Post subject: Reply with quote

Take a straight edge to it if you want , but it will be a little different while you are using the board.
Just sayin'. Confused
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speedysailor



Joined: 11 Sep 2007
Posts: 841

PostPosted: Sat Sep 08, 2012 6:16 am    Post subject: Reply with quote

zirtaeb wrote:

Modern boards being newer, the jury is still out. But in theory, a shorter board that doesn't flex over time should retain it's rocker longer...but...the wider board will pound it's bottom at the mast track harder, causing the softspot to accelerate quicker.
All that said, most serious slalom sailors change their boards about 50 sailing days into their procurement, just like their fins and sails.
I was wondering about this on my last two sessions. My 82 cm wide '06 board has been getting a pounding over the years. Definitely I've put in more than 50 days on it, but most of them have been with flat water. I don't see any real change in it's characteristics while on the water. My ankles exhibit more signs of the stress than it does. As I remember selling skis that foam cored one's lost their camber in a relative short time, 40 to 60 days tops. This became visibly noticeable when you pressed the two together in the mid-section. However, rec skiers average 5 days a year and often aren't bump skiers. It is extremely hard to find a wooden cored downhill ski today. Drew Bledsoe's Montana skis are all wood as I remember, but they are definitely expensive. Back to boards, I seriously doubt if anyone would notice the difference between a new board of the same make and model and my current one.
zirtaeb wrote:
A not as sensitive non competitor like me, going only for top speeds and acceleration FOR FUN, don't matter, as I get my sail size choice wrong, my fin size choice wrong, and my board size wrong more often than not.
And the softer ride, coupled with softer fins, might allow more play and room for error so a easier ride, like freeride gear, might allow me to go just as fast as the newest slalom kits.
That argument about a softer ride has been used with skis, too. The heavily used skis reserved for powder. I thought it was a crock, however, as did others. Some wanted a soft ski in powder, some a soft shovel and stiff tail, and some a stiff ski tip to tail. People are always looking for excuses to either buy new gear or keep their old. Most sailors can benefit from equipment that gives them more control of their ride. Heavily used stuff becomes sloppy. Going too fast can be scary. Getting catapulted remains a very unpleasant experience. Finally, I can't see how you wouldn't go faster on brand new kit than your old beat up crap.
swchandler wrote:


If considering buying a used board, or deciding whether to buy a new replacement board, I would recommend using the coin test to discern the condition of the bottom. If you hold a quarter between your thumb and forefinger and then tap the board all over the bottom in the footstrap area, you can hear the areas that have become softer. The sound is dampened, and it just isn't real crisp and solid as it should be. To better understand the difference, try the test in the nose of the board forward of the mast track, as it usually always remains very solid and crisp over time, because it just doesn't take the beating the rear of the board does.
I've been reading Carl Sandburg's 3 volume biography of Abe Lincoln lately. When the President thought someone was being ridiculous he would tell a droll short parable rooted in his experience. Chandler's post reminds me of a story taken from my days selling skis. Now, modern skis have a very pronounced side cut, but older skis didn't. You really can't see the sidecut in cross country skis, either. I told this story to one of the managers of the shop and we had a good laugh over it. A couple came in one Friday evening to shop for cross country skis. They brought along with them a Cambridge professorial type. I tried to sell them a pair of skis and mentioned the sidecut. Now most rec skiers won't notice the sidecut in a pair or cross country skis. Some skis like skating and racing skis have no sidecut. All the sidecut does is make it a little easier to turn the skis in track. The average run of the mill pair will have none because it's easier to build a ski that way and easier to hold a track. Questioning my sales pitch this guy takes out a pair calipers and measures the skis I'm trying to sell. Now, I did inspect my boards doing the quarter test and with a straight edge. I thought that the pitch changed when I tapped under the footstraps on a couple of the boards. However, I have to waste more of my time doing that trick to really be convinced of the test's efficacy. The straight edge (a metal yardstick) test was interesting as well. The most abused board I have, a Bic Blast, which I recently refurbished, definitely showed high spots on the bottom where the footstraps were. I think the Angulo Sumo which I have used often did also. The Naish Icon showed definite pitch changes under the footstraps but nothing to note when it comes to high spots on the surface. The Mistral CHS (carbon) Energy which I bought used and have sailed hard in chop showed a perfectly straight, flat tail. It's known for it's lack of rocker as well as the carbon which will hold the core's shape better. Now, I am planning on putting on the lab coat, taking the boards into the cork lined room and doing a full day of sound tests with the quarter. Remembering those days when I couldn't rub two nickles together, I certainly should get the most out of this coin. I will go over the areas below the mast tracks and have considered removing the straps so that they don't interfer with the vibrations. In addition I hope to be able to induce a couple of aeronautical engineers to assist me.
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swchandler



Joined: 08 Nov 1993
Posts: 5687

PostPosted: Sat Sep 08, 2012 3:05 pm    Post subject: Reply with quote

Watch out speedysailor, what you learn might come back to haunt you. You just might begin to develop this nagging thought that boards in your quiver have seen better days. Then you might find yourself being drawn to your local windsurfing shop endlessly entertaining the thought of buying something new.
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speedysailor



Joined: 11 Sep 2007
Posts: 841

PostPosted: Sun Sep 09, 2012 7:24 am    Post subject: Reply with quote

swchandler wrote:
Watch out speedysailor, what you learn might come back to haunt you. You just might begin to develop this nagging thought that boards in your quiver have seen better days. Then you might find yourself being drawn to your local windsurfing shop endlessly entertaining the thought of buying something new.
That is a fair warning, but I'm resolved to stay out of the local shops. The last time I walked into Sail World just to look around, I came home with a board. Seriously, though, I can't see the "soft spots" becoming problematic. My used boards definitely have them at the mast base and the footstraps, but it's just compressed core material isn't it? I was impressed with the tail on the Energy which had a perfectly flat bottom. In addition, I still have an 87 liter Maui Force which is practically new.
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swchandler



Joined: 08 Nov 1993
Posts: 5687

PostPosted: Sun Sep 09, 2012 2:12 pm    Post subject: Reply with quote

I have many older boards that are doing very well. In fact, I have so many boards right now it's doubtful that I'll ever buy another board in the future. However, if you are in the market to buy used, you'll get some added insight about a board's condition using the simple coin test. A board may appear to be in great shape, when in fact, it's showing its age in more hidden ways.
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speedysailor



Joined: 11 Sep 2007
Posts: 841

PostPosted: Mon Sep 10, 2012 7:43 am    Post subject: Reply with quote

Actually, I wanted to see some signs that I had used my boards which is really why I did the tests. It's like when the older bartender showed me the difference between an expensive scotch whiskey and the generic one. If I ever have someone from Mo. over, I can prove that I'm an experienced windsurfer. Someone can always pour cheap booze in an expensive bottle, but it takes a little more than alcoholism to know it's a ruse. The recently purchased Bic Blast was a mess when I bought it this summer. After having sat on the sales rack for two years while SUPs and bigger stuff came and went, the price finally came down. It also has a Tuttle box which must have stopped some potential buyers from going for it. Nevertheless, it did not surprise me that it has been sailed hard. I won't use it much unless I lose 50 lbs or so, but it definitely adds to the collection.
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