| Re: H18 SX diamond tension
[Re: WindyHillF20]
#186993 08/04/09 06:09 PM 08/04/09 06:09 PM |
Joined: Feb 2004 Posts: 3,528 Looking for a Job, I got credi... scooby_simon Hull Flying, Snow Sliding.... |
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Posts: 3,528 Looking for a Job, I got credi... | Sailmaker isn't sure about proper diamond tension. I think it will become trial and error to get it right. Best way as it will depend on 1, usualy wind conditions 2, usual wave conditions 3, Crew weight 4, spreader angle 5, luff curve and shape of mainsail.
F16 - GBR 553 - SOLD I also talk sport here | | | Re: H18 SX diamond tension
[Re: WindyHillF20]
#187011 08/04/09 08:56 PM 08/04/09 08:56 PM |
Joined: Apr 2002 Posts: 195 White Bear Lake, MN h17racer
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Posts: 195 White Bear Lake, MN | This excerpt from a mast/sail design manual may better elaborate.....
• Sail Shape & Boatspeed — There are several reasons to use prebend. The main benefit of prebend is to “match” the mast to the luff curve of your mainsail. If the prebend and luff curve are in sync, then the mast/sail combination will have a wider wind range potential. Net net is more speed. Another benefit of prebend is a more stable mast.
The most important use of prebend is to match your mast to your mainsail. If you sail in a class that has an optimum rake and prebend, your sailmaker will construct a mainsail with a luff curve and an overall design to match this mast curve. If a main is built with too much luff curve, the sail will be too full in medium- to heavy-air conditions and cannot be depowered. Assuming your mainsail is built with the proper luff curve to optimize the speed and versatility of the sail, your prebend should be adjusted to best match the sail. For instance, if the lower portion of the main is too flat in medium air, try reducing prebend by any of the methods discussed earlier. Working closely with your sailmaker to “match” the sail and mast bend will mean more speed on the racecourse. To have consistently good boatspeed through a wide wind range, you must shift gears to change sail shapes to suit the wind and wave conditions. If your sail and mast are in sync, the sail shape transition is almost automatic simply with downhaul/outhaul tension. If your sail and mast are not in concert, you will grind your way through the wind range with less boatspeed. Bottom line: spend time getting your prebend right. The results are dramatic on the racecourse.
Sail fast, Tom G
| | | Re: H18 SX diamond tension
[Re: h17racer]
#187062 08/05/09 12:32 PM 08/05/09 12:32 PM |
Joined: Jul 2001 Posts: 1,200 Vancouver, BC Tornado
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Posts: 1,200 Vancouver, BC | Prebend only applies to...prebend rigs...the Hobie runs the old "soft" rig...spreaders are not swept aft enough to make diamond tension bend the mast in the long axis (that's what a prebend rig does).
So, you adjust diamonds to control/limit bending in the short axis.
Get Rick's book...Cat Sailing for the '90's (available on this site's webstore). There is a detailed section on soft & prebend rigs and how to set them up. Any newer books/video's will not cover the old soft rig setups...they are so 1960-1980's :-)
Mike Dobbs Tornado CAN 99 "Full Tilt"
| | | Re: H18 SX diamond tension
[Re: WindyHillF20]
#187199 08/06/09 12:04 PM 08/06/09 12:04 PM |
Joined: Jul 2001 Posts: 1,200 Vancouver, BC Tornado
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Posts: 1,200 Vancouver, BC | Adding prebend is done by sweeping the spreaders aft and cranking on diamond tension. Older soft rigs did not have much spreader rake adjustment if any. Adding prebend to a TheMightyHobie18 will mean you'll need a custom cut mainsail and there not be class legal any more.
Placement of the diamond attachment points is not that relevant to generating prebend. There have been many iterations of the attachment points. Currently, have a single turnbuckle on the front of the mast is in fashion...makes it easier to quickly adjust tension on both cables at the same time. The carbon T mast runs the lower diamonds into the mast with the adjuster mounted in the mast base...a large single adjustment nut sticks out the bottom of the base.
Mike Dobbs Tornado CAN 99 "Full Tilt"
| | | Re: H18 SX diamond tension
[Re: WindyHillF20]
#187260 08/06/09 06:57 PM 08/06/09 06:57 PM | Scarecrow
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Unregistered | The attachment point does make a difference. Having the attachment on the front effectively gives you more spreader rake.
Last edited by Scarecrow; 08/06/09 06:57 PM.
| | | Re: H18 SX diamond tension
[Re: ]
#187330 08/07/09 11:34 AM 08/07/09 11:34 AM |
Joined: Jul 2001 Posts: 1,200 Vancouver, BC Tornado
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Posts: 1,200 Vancouver, BC | The attachment point does make a difference. Having the attachment on the front effectively gives you more spreader rake. Technically correct but you can still get to the same prebend with diamonds further aft on the mast...either by cranking more tension or sweeping the arma slightly more, or both. Main advantage of having the diamonds on te front is to make a single adjustment point, not two. The Tornado carbon mast no longer uses the single front mounts adjuster...the lower diamonds enter the SIDES of the mast near the base and connect to a single adjuster under the mast foot. Here you can see the lower diamonds connectint to the metal strap entering the mast section: Here is the adjuster bolt under the foot that the strap attaches to: Note how far aft on the section this is...no where near where the previous alu mast diamonds attached. C-mast prebends just fine.
Mike Dobbs Tornado CAN 99 "Full Tilt"
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