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  #1  
Old 02-22-2010
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Question regarding backstays on X-99

Hi everyone,

I have recently bought a X-99. The boat has got a fixed backstay which runs from the top of the mast down to the center back. Two running backstays from the 7/8 point of the mast to sb/bb back and two running checkstays running from 1/2 point of the mast to sb/bb center. The previous owner didn't use the fixed backstay and checkstays. He was the dutch champion for many years, if I look at the site of the current worldchampion they are also not using the fixed backstay and checkstays. So I don't bother about these controls at the moment.

My question is regarding the running backstays. I know that tightening the running backstay makes your mainsail flatter, so less draft, better in windy clause hauled conditions. I don't understand why it works that way, if the running backstays were attached to the top of the mast, I would. But they are running from the 7/8 point, which is the same point that the forestay is attached. I my logic tightening the running backstays would only bend the boat like a banana. This is probably not what is happening. Can anyone explain how this works exactly?

BR,

Martijn
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Old 03-03-2010
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Don't know much about the specifics ... I'm assuming from looking at a couple of pictures it's an aluminum mast with inline spreaders, but have no idea of how 'bendy' the rig is in general. Rules of thumb for a fractional rig with runners, checks, and backstay:

Runners: indeed control mast bend and headstay tension as you've stated.

Check stays: allow you to 'straighten the middle of the mast column when the runners are on which will increase the depth of main and allow you to a quick means to power up the main a bit.

Backstay: control the bend of the mast above the hounds (where your headstay meets the mast) allowing you to twist off the top of the main to de-power. I the rig is stiff enough (mast section thick enough, it can/will also control mast bend as it would on a masthead rigged boat.

This is all well and good IF the rig itself is flexible. My guess is that if your mast isn't all that flexible, then the checks and backstay are doing very little that effects sail shape. (the backstay isn't really in the right place to add tension to the headstay on a fractionally rigged boat... that's what you're runners are doing in addition to flattening the main.) I'm pretty sure you're rig isn't structurally runner depend, i.e., if you don't get a runner on, the mast falls down. That's what your backstay is doing even if it's not bending the top 1/8th of mast much.

Hope this gets you started... have fun! Looks like a fun boat!

Last edited by puddinlegs; 03-05-2010 at 05:28 AM.
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Old 03-03-2010
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Hi,

thanks for the reply. It is a very fun cruiser/racer boat indeed! It is an aluminium mast and it is pretty bendy. At least compared to the other (cruiser) boats in my harbour. I am pretty sure that the mast doesn't come down if you don't get the runners on, but I am not taking any risks there

I know the runners really do make a difference in speed, this is what the North timguide is telling me:

In light airs you sheet to the middle or just to windward of the traveller. The foot is eased so there is a lot of camber in the sail, the same with the cunningham. The halyard is loose, just enough tension as necessary to make the small wrinkles at the mast disappear. The running backstay is also loose and there is no tension on the checkstay and top mast stay.

In medium airs you sheet in to the middle of the traveller. The outhaul is tightened until near the black mark on the boom. Cunningham adjusts the camber. The halyard tension is close to the black band at the top of the mast. The backstay has medium tension, the checkstay has a bit tension to stabilise the mast curve. The top mast stay is loose. Kicking strap
is only used reaching or running.

In heavy airs you sheet 15 cm down on the traveller. Outhaul is set at maximum to the black mark, cunningham adjusts the camber. Halyard max to the black band, the backstay is set to maximum. The checkstay still adjusts the mast curve, therefore it is tensioned a little. The
mast top stay is loose. Kicking strap is only used reaching or running.

I am going with this for now, hope to find out more this year during class racing!
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Old 03-03-2010
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Quote:
Originally Posted by martijnburger View Post
...
My question is regarding the running backstays. I know that tightening the running backstay makes your mainsail flatter, ... But they are running from the 7/8 point, which is the same point that the forestay is attached. I my logic tightening the running backstays would only bend the boat like a banana. This is probably not what is happening. Can anyone explain how this works exactly?

BR,

Martijn
You use the running backstay to control the forestay tension. It has no particular or intended effect on the main.
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Old 03-03-2010
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How much and in what combination you use
each of the mast controls will depend primarily
on how the luff curve of the main is matched to
the mast bend and will vary with changing conditions.
The masthead backstay bends the mast to flatten
the main, but does very little to add forestay tension
on a fractional rig. The leech tension on the mainsail will
perform much the same function as the backstay while
sailing upwind, as long as it is sheeted tight.
The running backstays will be used to control the
forestay tension.
The check stays may be unnecessary most of the time,
but can be used to straighten the mast to make the main
more powerful.
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Last edited by COOL; 03-03-2010 at 12:31 PM.
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Old 03-03-2010
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Quote:
Originally Posted by COOL View Post
... will depend primarily
on how the luff curve of the main is matched to
the mast bend ....
Hmmm...won't these always be identical, regardless of controls, unless you rip the sail?
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Old 03-03-2010
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Hi Martjin,
Have you seen found this site International X-99 Association? Some in English some in Danish

Knut
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Old 03-03-2010
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Quote:
Originally Posted by sailingfool View Post
Hmmm...won't these always be identical, regardless of controls, unless you rip the sail?
Different sails may be cut with radically different luff curves.
Some sails are made with the luff curve approximating the
the max mast bend. These will be very full and draft forward
on a straight mast, and will require a bit of backstay, and no
checkstay, to flatten.
Another method is to design the sail with minimal luff curve,
which allows you to build more of the max girth into the roach
of the sail. This sail will require you to use more check stay
tension to keep the mast straight, and prevent 'over bend'
wrinkles from appearing.
If the class is typically sailing with no backstay,
and no check stay, the mains are likely cut with a
luff curve that matches the mast bend profile you would
get from mainsheet tension alone.
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Old 03-06-2010
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In strong winds we use our runners to help keep the mast from pumping. If the rig is as bendy as you suggest, your checkstays could serve this purpose.
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