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Depower question

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knot_moving
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Depower question

Postby knot_moving » Sun Dec 02, 2012 3:36 pm

Getting ready to think about how to build a 3:1 or 4:1 depower for ss turbine, that I'm riding with a Sector V2.

Just want to make sure I am not missing something stupid here. The total power/depower stroke is the combination of the bar movement from chicken-loop to bottom of stopper plus the distance from the top of the stopper to bottom of the swivel/pulley assembly - right?

Companies divide this up as a balance between being able to sheet in/out during gusts & lulls and depower cleat to trim in-out to control max power in gusts?

For racing it seems like fastest riding style is to keep kite relatively still (unless really low winds) and use high ratio depower to keep up with gusts and lulls.

When you are building 3:1 or 4:1 depower systems are you being 'religious' about keeping the relative split between bar throw and depower strap throw the same, or are you not worrying so much about that - and if you are keeping them the same, why?

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davesails7
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Re: Depower question

Postby davesails7 » Mon Dec 03, 2012 2:19 am

I think most keep the bar throw about the same. I did for my 4:1 system. Even if you do get good at trimming with the 4:1 system you'll still need to move the bar when you're tacking, jibing, pre-start, launching and landing on the beach...

The depower above the bar throw does have to be made longer if you go to a 4:1. Then you have to make the rear lines longer to compensate.

gbleck
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Re: Depower question

Postby gbleck » Mon Dec 03, 2012 9:57 pm

Set the 4:1 length a little longer then 4 times the decrease in length with the stock depower straps. Measure the fully powered and shortened lengths. I think most strap systems are 2:1 but don't quote me. Make sure you factor in the distances for the turn on the blocks. Your 3:1 or 4:1 length depower set up will be longer then a stock 2:1 so you either have to use more space before the center line y split or add longer leader lines to the outside steering lines which is quite simple and has the advantage of being easy to reverse if you want to sell the bar. Remember to lengthen any centerline flagging lines the same amount if you add outside line extensions. Or you could just buy a stock bar from ozone all set up nice but what's the fun in that?

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davesails7
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Re: Depower question

Postby davesails7 » Tue Dec 04, 2012 4:38 pm

gbleck wrote:Set the 4:1 length a little longer then 4 times the decrease in length with the stock depower straps. Measure the fully powered and shortened lengths. I think most strap systems are 2:1 but don't quote me. Make sure you factor in the distances for the turn on the blocks. Your 3:1 or 4:1 length depower set up will be longer then a stock 2:1 so you either have to use more space before the center line y split or add longer leader lines to the outside steering lines which is quite simple and has the advantage of being easy to reverse if you want to sell the bar. Remember to lengthen any centerline flagging lines the same amount if you add outside line extensions. Or you could just buy a stock bar from ozone all set up nice but what's the fun in that?


I think you're over estimating the amount of extra length needed to match the length of a stock 2:1 system.

Assuming your existing depower strap gives you 6 inches of front line adjustment:
If you go with 4:1, and want to have 6 inches of front line adjustment, you will need to make the length of the 4:1 system 12 inches. This is because when you pull it all the way block to block, the system is about half as long as when you started (not counting the size of the blocks and the knots).

If you go with a 3:1 system though, you don't need to make it any larger at all to get the same 6 inches of travel (except for the added size of the blocks and knots). When you pull the 3:1 system to full depower (block to block) the length goes all the way to 0 (again, not counting the knots and blocks).

I'll draw a picture later.

gbleck
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Re: Depower question

Postby gbleck » Tue Dec 04, 2012 11:25 pm

Yes the 4:1 system will be around 2x the length of the stock... and that is 4 times the amount the 2:1 shortens. So figure adding around the length of the 2:1 in extensions. Don't forget to account for knots and splices when ordering line. Having a bit of extra is great though as it makes good replacement line if your buying the good stuff.

knot_moving
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Re: Depower question

Postby knot_moving » Wed Dec 05, 2012 3:57 am

davesails7 wrote:If you go with a 3:1 system though, you don't need to make it any larger at all to get the same 6 inches of travel (except for the added size of the blocks and knots). When you pull the 3:1 system to full depower (block to block) the length goes all the way to 0 (again, not counting the knots and blocks).

I'll draw a picture later.


Thats why I was going to start with the 3:1 - I think I will have enough line using existing depower line and moving it from below the bar to above the bar. Only thing is I will lose about 3" of throw on the bar (for blocks), unless I add small extensions to the steering lines - guess it will be a good excuse to practice splicing loops with brummel knots :)
anyone carried a small fid onto an airplane recently?

btw thanks all for the advice - will do the conversion over the holidays I think, unless by some miracle we start getting some wind here :angryfire: :angryfire: :angryfire:

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davesails7
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Re: Depower question

Postby davesails7 » Wed Dec 05, 2012 3:59 am

Maybe we are talking about the same thing here and just using different terms.

Anyway, there has been so little wind here, and I am so bored. I didn't realize how bored I was until I spent the time to make this picutre haha. The red circles are the pulleys/blocks, the blue square is the cleat, the x's are the fixed points.

So what I was talking about as the 6" of front line adjustment is the amount that the front lines can be shortened going from full power to full depower.

On a 2:1 system, which is the stock system on all bars including ones with depower straps, the size of the depower system is pretty much the length you can shorten the lines other than the size of the blocks and the knots. When you pull in all the way block to block, the length of the depower system is almost nothing.

The 3:1 system is the same. When you pull in all of the depower and go block to block, the size of the depower system goes down to nothing but the size of the blocks and the knots.

The 4:1 cascading system is different though, when you go block to block on the green line, you only are reducing the overall length of the depower system by 1/2. The upper pulley is now in the center of the black line.

So when you go from the stock 2:1 to a 3:1, you don't need to lengthen the travel of the system (unless you want a wider range of depower than the stock system gives you). When you go to a 4:1 system though, you need to double the length of the depower system to keep the same amount of travel of the system. So if you're 2:1 system shortened the front lines by 6", you need a 12" long 4:1 system to depower the front lines by 6".
Attachments
Depower.jpg

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davesails7
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Re: Depower question

Postby davesails7 » Wed Dec 05, 2012 4:03 am

knot_moving wrote:Thats why I was going to start with the 3:1 - I think I will have enough line using existing depower line and moving it from below the bar to above the bar


Which bar are you using? North? For the North bar you might as well just get a new, longer piece of line for the depower from West Marine. I think it cost around $12 for 15 feet worth of amsteel blue and they shipped it to the local store for free.

As far as splices, I haven't spliced mine yet. I've got bowlines in my system until I get it adjusted the way I want. Lack of wind here also, so haven't got it dialed in yet

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Re: Depower question

Postby KristianE » Wed Dec 05, 2012 10:08 am

Is it impossible to get a suitable double block for the upper part of a 4:1 setup?

lander
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Re: Depower question

Postby lander » Wed Dec 05, 2012 1:23 pm

KristianE wrote:Is it impossible to get a suitable double block for the upper part of a 4:1 setup?

I use a double block on the upper and is happy with this...(also tried the 3:1 but still thought is was too little ratio, and did not make the trimming as easy as I want it).


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