As i learn a little more and work the bugs out of my p19 i find myself questioning the diamond wire tension on my boat.
The diamond wires on my mast are not able to touch the mast AT ALL, they are super duper tight. From others estimating by the " diamond wire touches XX inches up the mast" i find myself questioning the settings on mine even more. Also since i plan on buying new ones soon it would be great to know a good and safe estimate to use. Mostly safe though.
Thanks in advance,
-Matt
estimated diamond wire tension help/guidance
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Posted: Oct 03, 2011 - 02:58 PM
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Posted: Oct 03, 2011 - 03:38 PM
According to the P18 manual:-
"Adjusting the tension of the diamond wires should be done with care, after the mast has been stepped, but before the sails are hoisted, adjust both wires to the same tightness, if one is looser than the other, your mast will bend more on one tack than the other. Push/squeeze both wires towards the mast with equal tension at the same time. The wires should touch the mast at least 12 Inches above the lower attachment point, but not more than 20 inches above. If diamond wires are too tight, your mast will not bend, and undue strain will be put on these wires."
http://www.thebeachcats.c…707&g2_imageViewsIndex=1
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TurboHobo
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P18
G-Cat 5.0
P16
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Posted: Oct 03, 2011 - 04:28 PM
That's if you use mast rotation to bend the mast. I think many (higher performance cats) today are pre-bending their masts and using downhaul to flatten the sail. Pre-bent masts have very high tension and you will not be able to touch the wire anywhere to the mast. Get a loos gauge.
http://www.mauriprosailin…lboat-tension-gauges.htm
Google "catamaran pre-bend loos gauge"
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Uwe
94 Prindle 19 - "überKat"
DFW, TX
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Posted: Oct 03, 2011 - 04:56 PM
More spreader rake will bend the mast more when a gust hits or you apply diamond wire tension. More mast bend equals flatter sail. Good for light crew or letting the sail depower when windy. Heavy crew or choppy conditions, you might want to keep the sail powered up by having less spreader rake.
Once you set your spreader rake, then it's on to diamond tension. More tension creates a flatter sail because it will pre-bend the mast. Less tension give you more power with a straighter mast. Tension too loose will let the lower part of mast bend sideways and close your slot. This was the problem with using loose wires (that you can touch to mast) and rotation to bend the mast and why pre-bend is more common now.
I have my spreader rake about 2.75 back and about 31 (that's loose) on loos gauge. Right now I want the rake to make the mast bend on a gust since I sail on lakes with light crew. Once I get used to the boat, I plan on putting in less rake (down to 1.5"?) so it wont spill off as much wind and keeps the sail full.
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Uwe
94 Prindle 19 - "überKat"
DFW, TX
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Posted: Oct 03, 2011 - 05:15 PM
If your sails are cut for prebend, MX sails should be. Who is the sail maker?
Spreader Rake: 1 3/4"- 2"
Mast Prebend: 2" ( this will mean approximently 500lbs of tension on the spreader wires )
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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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Posted: Oct 03, 2011 - 08:36 PM
smyth main.. probably from his first run of MX mains from the late 90s(sail has def seen better days).
also, when using the halyard to unhook the sail, you can pretty easily see the top of the mast bend(i assume it would do the same with downhaul cranked too). -
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Posted: Oct 04, 2011 - 12:42 PM
Matt922,
Your mast and the Smyth sails were designed and manufactured long before this current age of the pre-bent mast. Turbohobo has quoted the P19 manual correctly, and the very next paragraph in the manual warns not to over tension the diamond wires. Loosen the wires to the 12" setting (measured from the mast dog hole at which the diamond wire attaches) and see how your boat sails. Once there, use the spreader settings at about 1.5 inches and experiment with the mast rotation after every tack or gybe. The newer pre-bent masts use a main downhaul that is 10:1 or higher. The engineering is completely different. Rig your Prindle the way it was designed. I would hate to read about your dis-masting. For the record, I use closer to 20" setting in big wind offshore, less in inland lakes with lighter air.
Bob
Prindle 18-2 #244
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Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
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Posted: Oct 04, 2011 - 05:38 PM
re: down haul, i'm not exactly sure how to count downhaul ratio, but i have 3 pulleys on each side, shared by a pulley in the middle(mounted on mast), along with a block on each side of the sail.
this boat actually lived at FWYC(randy's home yc) for a year or two, so i'm very careful on the things i change about it without being absolutely certain. -
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Posted: Oct 04, 2011 - 06:26 PM
Sounds like 8:1 That's all you need and all I run on my F18. I used a cascade on my 5.5 to get to 16:1 and pulled the head plate out of the sail.
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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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Posted: Oct 04, 2011 - 07:13 PM
here ya go, drew it up in MS paint
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Posted: Oct 04, 2011 - 09:52 PM
He quoted the p18 manual. P19 works great with pre-bend.
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Uwe
94 Prindle 19 - "überKat"
DFW, TX
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Posted: Oct 05, 2011 - 03:54 PM
This is a good pic of what the bottom of the downhaul should look like on and 8:1
The top which is not in the pic is a double hanging off either side of the sail.
The green line in your pick is for the cascade which is a single hanging off the sail and a double on a sort piece of line going thru the single and ending on the clamcleat.
Edited by nacra55 on Oct 05, 2011 - 04:09 PM.
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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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Posted: Nov 03, 2011 - 03:24 PM
Uwe, are you saying that you pre-tension your diamond stays really tight and do not rotate your mast?
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Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
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Posted: Nov 03, 2011 - 06:46 PM
Yes, diamonds are really tight.
I do not rotate the mast to depower the sail, I use a 12:1 downhaul to flatten it. I try to keep the mast rotated so that it provides a nice profile to the wind.
I do rotate the mast and use barberhaulers when going downwind.
Check out chapter 19 in "Catamaran Sailing For the 90's". Amazon has it. The entire chapter is written by Randy Smyth and covers tuning the P19. I highly recommend that book for any P19/P18-2 owner. He does say that the dacron cross-cut sails are not designed for pre-bend. I'm using the mylar sails so it works well.
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Uwe
94 Prindle 19 - "überKat"
DFW, TX
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