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Author Topic: mast step position  (Read 10313 times)
iceboater000
Guest
« on: February 08, 2009, 01:38:48 PM »

estonian championships took place this weekend. it was my first dn race(i have sailed opti for 4years).
on saturday the wind was about 4-6knots, i have only one sail, which is quite flat. i didnt move very well, until  the only race on saturday ended and i moved my step all the way back, which is exactly opposite to
http://webpages.charter.net/jackandkelly/c2guide.html my boat hiked very fast and moved fast to. on sunday we had 5 races and the wind was about 14knots, step was as back as possible. i moved very fast and got higher than others, but the boat hiked too much(it was very unstable), i tacked 50metres  before others to layline but, my boat hiked too much, if i tacked at same place as others, then it was impossible to sail. i was told after the race that i would put the step all the way forward, then the boat will be more stable, which is also opposite to http://webpages.charter.net/jackandkelly/c2guide.html . someone told me that it depends on masts stiffness. by the way i weight only 60kg, im young Cheesy. i hope fore discussion on that topic.
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DN 805
Class Member
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Posts: 267


« Reply #1 on: February 08, 2009, 02:43:00 PM »

Every sailor must take several things into consideration when tuning the boat.
1.  The weight of the sailor and his strength to trim the sail.
2.  The flexibiity of the mast and the fullness (or flatness ) of the sail.
3.  The flexibility of the runner plank.
4.  The ice conditions, fast surface or sticky.
5.  Wind velocity.

Keep a book about your DN sailing.  At the end of each day write down the ice condition, the temperature, the wind velocity, what mast, sail, runners that you used, what settings you had for the mast step, the forestay, the side stays, the halyard, the mast rotation. 

In your book write down details about your mast (how much it flexes), your runners (what crown and angle), your sail.
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Over time your book will show you which are the fast settings for you and your boat and many different sailing condition.

good luck
DN 805
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ROBERT RAST
Class Member
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Posts: 17


« Reply #2 on: February 09, 2009, 03:36:48 PM »

Sounds like you went from one extreme to another. You should make small adjustments  and remember where you were.Being  some what lighter than some skippers 165lbs, I  had a hard time getting masts to bend early on until i developed my own. If the mast is too stiff,you are hiking all over , move the mast step forward or rake the tip back or loosen side stays.
If the mast is too soft it will bend easily and be comfortable to sail but not fast.You should be able to get the mast to bend when up to speed and the boat should only hike up a little and be able to get it back down by bending mast and sliding down into cockpit.
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dn4379
ADMIN

Posts: 55


« Reply #3 on: February 22, 2009, 08:13:44 AM »

 Moving the mast step is a primary way to control the bend in the mast.  More mast bend (sideways) will do two things; flatten the sail, reduce the ability of the wind to hike the boat up. ( As the mast bends it also falls back and to the side, reducing hiking force)
  For discussion, let us assume that no side stay length changes are made.  A two inch change in the mast step position with a change in head stay length to keep the same tension on the side stays will noticably change the behavior of the mast.  If the step is moved forward the mast will bend easier for the same amount of main sheet tension.  Move the step back and the mast will behave more stiffly, the sheet will be harder to pull, the boat will hike easier which is what forced you to sail higher and slower upwind and I will bet you had to sail lower downwind as well. 
  What is really going on here is small changes in the angle between the headstay and the long axis of the mast.  Small changes in this angle cause large changes in the compression forces on the mast which cause the mast to bend, or collapse and break as we have all seen. 
  Generally we will  move the step forward ( rake the mast more backward) when the mast is not bending enough. An example would be lighter air when we want the mast to bend but not have to pull so hard on the sheet to make that happen. Who need a tight leech in light air?!  Sometimes just a half a centimeter longer on the headstay will rake the mast back and loosen the side stays just enough to get a little more bend or to reduce the hiking forces just enough.  Too much rake and the boat will sail "too easy"; it may go fast but will not point upwind, will not go low enough downwind. I call this reaching thru life. 
  You can make yourself "heavier" by moving the plank forward.  This moves your body's center of gravity further away from the healing axis of the boat ( straight line form front to leeward runner) which gives your body more leverage to hold the boat down.  This will allow you to stand the mast up for more power but there are limits to this.  Jan Gougeon is about 65-70 Kg and sails with his plank quite far forward, his mast is more flexible than most and his step is more forward that mine (82 kg).  Jan does well in all conditions by using these adjustments to make his boat work for him and his body type. 
  I could go on for hours but understanding the concepts of mast rake-mast bend and plank position-righting moment are major to understanding how to get your DN to fit your body type and the sailing conditions of the day. Start there.  Try it out and come back with more questions.  There is no end to questions and answers in this sport; we are learning all our lives.
       Maybe see you on the ice next year,
                                                                John Harper US4379
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iceboater000
Guest
« Reply #4 on: February 25, 2009, 04:14:52 AM »

but why i need to bend the mast in light air-how can be sail flatter when mast bends??
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Paul Goodwin - US 46
ADMIN

Posts: 100



WWW
« Reply #5 on: February 25, 2009, 05:49:34 AM »

One of the primary ways a sailmaker puts draft (fullness) into a sail is by putting a curve on the luff (leading edge) of the sail.  When the sail is put on a mast, it straightens the leading edge of the sail and pushes the extra sail cloth into the body of the sail, creating draft.

When the mast bends, it pulls out the extra sail cloth, flattening the sail.

In light air, the forces on the mast are relatively low, and it can be difficult to get the mast to bend.  As the boat starts to accelerate, it can reach a speed where the fullness of the sail creates a lot of drag, and limits the top speed.  If you can get the mast to bend, and flatten the sail, then the top speed can be increased.

Here is the tricky part.  If the mast doesn't bend, you can't reach the top potential speed of the boat.  If the mast bends too early or too much, you will not have enough power to accelerate, and may not ever reach top speeds. 

As a boat accelerates, the apparent wind increases, and increases the forces on the mast.  If everything is tuned properly, the mast will bend in harmony with these increasing forces, and the boat will have quick acceleration "through the gears", with proper timing and amount of mast bend to reach it's maximum speed. 

The required tuning techniques to get the correct mast bend come with time, practice, and careful attention to what works under different conditions - and separates the top sailors from the rest of us.  Don't be afraid to ask some of the top sailors on the ice what they are changing to adapt their boats to different ice and wind conditions - just don't do it in the middle of a World Championship.
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Paul Goodwin
DN US-46
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