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Author Topic: Mast Rake and shroud tension  (Read 10018 times)
mikest29
Newbie

Posts: 19


« on: January 13, 2015, 02:25:34 PM »

I am new to ice boating .  I bought my first DN this year and am wondering about the correct amount of mast rake and stay tension . My stays are very loose . I have been hobie catting for a long time and know there is a specific tension that you want on the stays. Any suggestions?


Thanks

Mike

My boat is older hull style with an aluminum mast.
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DN5358
Newbie

Posts: 109



« Reply #1 on: January 13, 2015, 07:18:42 PM »

Ron provides a tuning guide that is a great place to start the voodoo magic that is tuning a dn. 

http://iceboatracing.com/dntuning.html
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KB [us5219]
Class Member
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Posts: 248



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« Reply #2 on: January 14, 2015, 09:38:08 AM »

So first a disclaimer:  Aluminum masts don't bend like glass and carbon ones.   Some aren't designed to bend much at all, while others are pretty nimble.  If the mast bends past a certain point it will kink, bend, or break.  And with aluminum spars you want to be careful not to push that limit.  IF you know the brand of spar, someone here might be able to give you some pointers on how much bend it could take.

Generally speaking, stay tensions will vary based upon sailor weight, plank stiffness, and spar stiffness. 
IF your spar is bending TOO MUCH, then you will want to do one or more of the following:
(In more or less this order):

Lower Halyard (Especially if you cannot two-block when sheeting as hard as you can).
Shorten forestay (may also improve pointing). 
Tighten side stays.
Move mast base AFT
Move Plank AFT
If it bends too much while you are sailing SHEET OUT!  A few inches of sheet might be all it takes to save your spar.

OF course you may reverse those items if you don't have enough bend.
Remember that adjusting the forestay, changing mast base, and moving plank all affect the side stay length and tension.

For starters -  You might set up a boat with the mast base and plank (if they are adjustable) in the second from furthest aft positions.
With the side stays loose, see if you can adjust the mast rake (by forestay length) to angle of 18 degrees (+/- 2 degrees) of rake.   I use a level protractor gauge (at 72 degrees) or smart phone might work, or just stand back and Eyeball it with other boats set up around you.
Then adjust the side stays to a tension that allows them to be easily fastened while you are standing on the plank.  Unfortunately, limitations in adjustability on your stays may be an issue.  You may have to adjust your mast base or plank position to help get around this if you cannot adjust your stays enough.

Finally how do you measure bend?  Well most of us eye-ball the forestay (which is taught and makes a straight line) and can observe the bend about halfway between the base and the shroud hound.  Aluminum masts might only tolerate 2-4" of bend out of column, while Carbon and glass masts routinely go 8-10" and often way beyond.  Bend should be appropriate for the wind.  In very light air, you will likely have almost no bend.  Heavy air, when rounding weather marks you should see near the Maximum.

These things work slightly differently for each person and each boat.  I am sure you will find many who disagree with my approach, but these are things that I think will help you.  Let us know what works and doesn't work for you.  This is a trial and error process that lets you tune your boat to your weight and sailing abilities.
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DN 805
Class Member
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Posts: 267


« Reply #3 on: January 14, 2015, 10:29:24 AM »

Kent has done a great job of describing set up.
I  have raced DNs beginning in 1956, including several different brands of aluminum masts.   The last championship won with an aluminum mast was Mike O'Brien winning the Gold Cup in 1989 in light to moderate wind on Lake Champlain.
We currently carry the sail low on the mast but aluminum masts are generally stiffer than current composite masts, so ok to carry the sail higher, but not to the top of the mast.    Rather than measuring the angle of the forestay, just have the rake set so that at rest the boom is horizontal with the back of the boom approx. 14" above the tail of the boat.   It is possible you may not trim block and block when sailing.
As for side stay tension, OK to have them snug when you're standing on the plank.     
Most pivoted the mast base in the aft most hole.  The mast bends more in the center hole because it rotates more.
I assume the horizontal distance from your steering chock to the bow tang is approx. 4". (longer nose on new boats)  I'd place the mast step 38" or 39" from the steering chock.   (be sure the boat construction accommodates this dimension)   If you go too far back, it will be difficult to get the boat to turn off the wind.
Kenyon brand aluminum masts seemed to have been the most durable.   The original Norton mast also durable.   The Norton wing was fast and more flexible, bending and kinking.   A stick inside solves that problem because it keeps the walls from collapsing.   

Have a good day on the ice.
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mikest29
Newbie

Posts: 19


« Reply #4 on: January 14, 2015, 11:03:52 AM »

Thanks guys. My boom is the right height and The mast rake seems fine. Standing on the plank and having the shrouds snug is what I wanted to know.
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