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How Much Downhaul Tension?? #82248
08/10/06 04:25 PM
08/10/06 04:25 PM
Joined: Aug 2006
Posts: 10
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nhsailor Offline OP
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nhsailor  Offline OP
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Joined: Aug 2006
Posts: 10
How much downhaul tension is correct? I've got an old (1979) H16 with a little curve in the mast near the top. If If I rig a 3:1 to put some tension on the downhaul I just exagerate the bend in the mast.

Is it common to crank on the downhaul to the point of bending the mast??

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Re: How Much Downhaul Tension?? [Re: nhsailor] #82249
08/11/06 07:23 AM
08/11/06 07:23 AM
Joined: Sep 2003
Posts: 270
Nepean (Ottawa) Ontario Canada
Frozen Offline
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Frozen  Offline
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Joined: Sep 2003
Posts: 270
Nepean (Ottawa) Ontario Canada
I am not an expert but I can just tell you from my windsurfing past, that the sail is made in such a way that when it is pulled down by the downhaul and pulled out at the clew the mast naturally bends. This preloads the top of the sail in particular and the rest of the sail generally and so that it maintains shape in stronger wind. ie. the sail flaps less. This makes it more efficient.

If on the other hand your mast is damaged or weak this may change things. What direction is the mast bent?


Cheers
Alan F

Tiger
Re: How Much Downhaul Tension?? [Re: nhsailor] #82250
08/11/06 10:03 AM
08/11/06 10:03 AM
Joined: Apr 2005
Posts: 292
Ontario, Canada
Captain_Dave Offline
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Captain_Dave  Offline
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Posts: 292
Ontario, Canada
I cannot say what the "correct" amount of tension is because it is specific to the weather on any given day and I am still learning this myself. However, it is normal for your mast to bend when significant downhaul is applied.

The best explanation of this I have seen is in one of Rick White`s videos. Essentially, the luff of a sail is cut as a curve. It is not a straight cut as seen when the sail is laid flat on the floor (without battens). When the sail is then put onto a mast - which of course is straight - this causes the sail to assume a full or airfoil shape (in cross-section).

Applying your downhaul IS supposed to bend the mast. This allows the sail to assume a flatter shape because the "bent mast" better conforms to the curved cut of the sail`s luff.

Flatter sails are generally desired in heavier winds because a flatter sail has less power that a fuller sail.


Hope this helps,

Dave

Re: How Much Downhaul Tension?? [Re: Captain_Dave] #82251
08/11/06 03:18 PM
08/11/06 03:18 PM
Joined: Sep 2005
Posts: 1,187
38.912, -95.37
_flatlander_ Offline
old hand
_flatlander_  Offline
old hand

Joined: Sep 2005
Posts: 1,187
38.912, -95.37
general rule of thumb.

Rig boat for wind conditions and apply downhaul until the wrinkles in the luff disappear.


John H16, H14

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