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Nacra 5.5sl jib block position #242032
01/04/12 09:32 AM
01/04/12 09:32 AM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Andinista  Offline OP
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Hi,
I'm learning to trim my new boat and I'm having troubles with the jib. The 4 way system is missing but I'm not very interested in having a wire on the tramp, so I used a line instead. Eventhough the line streches, I believe the end result is not too different in terms of geometry. I played with traveller and also moving the block in and out and concluded the following:
- The ability to point high is pretty bad if you keep the block always out (or attached directly to the traveller)
- I felt that the traveller should be more forward than what the track allowed. This is because the jib leech was always a bit loose and opened up in the upper part, as opposed to the foot that was straight and firm. A simple test shows the same fact I think: I took the block out to find the good position by hand. I chose a fixed position side to side (above the foot strap) and moved forward and aft, to find the point where leech and foot were tensioned equally. That point was about 15 or 20 cm or so forward of the jib track. The sails are not the originals of the boat, so it's no such a weird idea that there is something wrong with the sail cut. (Though I'm very open to hear that there's soemthing wrong on the "end user" side..). Then I made a change to my jib system to test my theory and it seemed to work better: I passed the line from one traveller to a fairlead in the center of the front beam and to the other traveller. It seemed better but now I was limited in range because of the line stretching (line goes up and leaves no room to tension the jib sheet). But there are possibilities to fine tune that, and it seemed close enough.

What do you think? should I be looking at something completely different to solve this problem?

Here is a picture showing the jib leech open (click for bigger image):

[Linked Image]

Last edited by Andinista; 01/04/12 09:37 AM.
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Re: Nacra 5.5sl jib block position [Re: Andinista] #242051
01/04/12 01:01 PM
01/04/12 01:01 PM
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South Carolina
Jake Offline
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Are you trying to sail to weather in that picture? If so, you could use a lot more mainsheet tension.


Jake Kohl
Re: Nacra 5.5sl jib block position [Re: Andinista] #242052
01/04/12 01:14 PM
01/04/12 01:14 PM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Andinista  Offline OP
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I am. I agree, but I had troubles filling the jib, no the main. It didn't seem to me that tensioning the main would change that significantly.

Last edited by Andinista; 01/04/12 01:17 PM.
Re: Nacra 5.5sl jib block position [Re: Andinista] #242057
01/04/12 01:58 PM
01/04/12 01:58 PM
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Jake Offline
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The jib and the main twist do match..but they both need to be in considerably further / sheeted harder. I use the spreaders as a sheeting reference for the jib...and I would sheet the jib somewhere just outside of the tip of the spreaders in that kind of breeze. It should come in a little further as the wind gets lighter and be just inside the spreaders in the light stuff. So I guess, start with the sheeting arrangement to find a way to get it to that point. Then move the sheeting blocks fore and aft to get the jib to twist off at a similar rate as the main as you ease both off when cracking off the wind a little.

Some vectran would work well as a cable replacement with minimal stretch and still be a good bit softer on the knees.


Jake Kohl
Re: Nacra 5.5sl jib block position [Re: Andinista] #242059
01/04/12 02:26 PM
01/04/12 02:26 PM
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Santiago, Chile
Andinista Offline OP
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Thanks Jake. Yes, on my "beach test" the jib was where you mention with respect to the spreader , I used similar criteria on my old cat. As you say I need more tension but I couldn't, the clew pulley touched the jib block. It seems I'm not on the wrong path, I will have to find a more rigid line and maybe cut some length to my jib block, for example removing the fast shackle that I added. (I did like it though...). I will also verify that both sails twist off similarly, I didn't think of that.

Re: Nacra 5.5sl jib block position [Re: Andinista] #242062
01/04/12 04:26 PM
01/04/12 04:26 PM
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Jake Offline
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Another way to set your jib twist is to sail to an upwind setting and fall off the wind. Look for both upper and lower tales on the jib to break (stall) at about the same time. This is probably more important that comparing the main/jib twist. This way you know your jib luff is pretty parallel to the breeze and the top and bottom trim match and the sail is providing an equal amount of driving force all the way up. However, if you're bobbing and weaving in the waves, a little bit of twist in the top will probably keep more air attached (some part of the sail will be in good trim as the boat 'tomahawks' through the air) and drive a little more consistency...so you want a little twist in rough conditions and none in smooth stuff.

I think most of that came out of Rick White's book.


Jake Kohl
Re: Nacra 5.5sl jib block position [Re: Andinista] #242069
01/04/12 08:45 PM
01/04/12 08:45 PM
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japan
erice Offline
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here's a pic of what presumably is a standard 5.5
make sure your jib block runners are in the same position

http://www.thebeachcats.com/classifieds/showfull.php?product=11728&bigimage=DSC00406.jpg

the 5.5 is very very similar to the 5.2 and on the 5.2 the best jib sheeting position for pointing is on the tramp about 30cm in from the runners...

as jake says you need 2 sets of tell-tales to determine the correct fore-aft position, which is when they are both breaking at the same time

better pointing is slower, but it if you need to tack often, you get upwind faster

footing off a little is faster but you'll only get upwind quicker if you don't have to tack much...

it's a complex equation answered more by your own situation than how other people setup their boats for other places...

edit: if the jib is not from a 5.5 all bets are off, apart from the difference in cut and curvature do you know how the lengths of the 3 sides compare to that of the factory sail?

Last edited by erice; 01/04/12 09:08 PM.

eric e
1982 nacra 5.2 - 2158
2009 weta tri - 294
Re: Nacra 5.5sl jib block position [Re: erice] #242071
01/04/12 09:03 PM
01/04/12 09:03 PM
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catandahalf Offline
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I will check with my son to make sure this is correct, but I do remember having the ability to adjust the jib lead in and out in order to control the slot as Jake mentioned. On the 5.2 we cut slots in the tramp and placed the wire jib lead under the tramp for comfort smile On the 5.5 we ran a wire across with an adjuster on the opposite side.

Make Sure the rig is TIGHT! Upwind is a precise lane that requires quality tuning and concentration. When sailing upwind the skipper and crew should be hiking flat and foiled with sheet control at all times...well balanced - the boat will drive itself, give or take a wave or two...Cheers to great winds!

Re: Nacra 5.5sl jib block position [Re: Andinista] #242073
01/04/12 10:10 PM
01/04/12 10:10 PM
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South Carolina
Jake Offline
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great looking boat BTW!


Jake Kohl
Re: Nacra 5.5sl jib block position [Re: Andinista] #242079
01/05/12 09:48 AM
01/05/12 09:48 AM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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OK. So I'll get some tell tales. Do they go in very specific places on the sails? A good book seems a good idea too.

Regarding the rig, this time I tensioned it pretty hard, following Bert's advice. I rig the boat by myself (my crew is a bit young) so I wasn't quite confident on using the mainsheet with the main up to release tension on one shroud. Instead, before hoisting the main, I took the mainsheet system out of the traveller and attached it with a short line to a rudder pin. Then used the mainsheet to tension a trap wire of the same side. It was pretty effective. First I tried something similar but tensioning the jib halyard but it didn't work nearly as well. But I'm a bit afraid I might have got a bit too far. When I hoisted the main and tensioned the downhaul I noticed that the upper part of the mast curved to one side. I tensioned the opposite diamond wire to straighten the mast (side to side) but the tip of the mast still curves to the side when I rotate the mast (it happens evenly to both sides). The wind seems to compensate that and keep the mast in column, but maybe it's not the way it's supposed to be done. I wonder if I'mm applying too much rig tension or too much diamong wire tension. I hear talking about pre-bending the mast with the diamond wires, which wasn't happening yet. (And I'm not sure if it's the right thing to do, it seems to take lot of tension). I also noticed the mast was quite harder to rotate, so I am guessing I can go back a little bit on the rig tension. Quite confusing for me, so any advice is wellcome, including a good book or a specific tuning guide for this boat, I haven't found one yet.
Thanks again.
Andrés


Re: Nacra 5.5sl jib block position [Re: Andinista] #242085
01/05/12 11:28 AM
01/05/12 11:28 AM
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Jake Offline
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Rick White's book is a good one to get started on these things. I'm sure it's available in the on this site...I think I got mine from Amazon some time ago.

Don't get crazy over rig tension. It doesn't really add that much to the boat performance. The leeward shroud is ALWAYS going to be slack when trapezed and too much tension makes mast rotation difficult (really important to have good rotation on a boomless boat). Downhaul, wind pressure, trapeze weight, etc. all make the mast bend which makes it shorter. The boat flexes too. Rig tensions is the last thing I worry about. I usually hold on to the trap wire off the rear beam and let my crew pin/screw the shroud down at that point - and don't worry about it any more. Diamond wire tension is 20X more important that rig tension.

There are a lot of different ways to set your ideal diamond wire tension...some will advise to lay the boat over on it's side and hoist the main to the top of the mast (pinned at the bottom with the downhaul) without the luff in the groove. Adjust the mast prebend to the shape of the luff. I'm not sure how all that works so I usually go by the tuning guides for my boat and use a wire tension gauge. Diamond wire tension really makes a big difference in the light air speed. In heavy air, correct tension reduces how big the adjustments need to be to respond to puffs...and it does help the boat respond to gusts a little more automatically. (Where legal), I sometimes adjust diamond wire tension between races.

Diamond wires can carry a LOT of tension - up to 800 lbs of tension on each wire in some cases. Depends on the boat/mast, geometrical arrangement, and what the system can withstand.

During this year's Steeplechase, I forgot to address our diamond wire tension that was left on a moderate-light air setting from my last regatta. I noticed on the long upwind 2nd day that our windward diamond wire was getting slightly slack when depowering in the times we had extended pressure and gusts (HARD on the downhaul and mainsheet). We were plenty fast...and it probably gave us a little edge when the pressure was down - but I should have had it a little tighter to make the boat a little more manageable while in the pressure.

On my A-cat - diamond wire tension makes a gigantic difference in the boat speed from 8 to 12 knots of breeze. One day I'll get some time to make a live adjustable diamond wire setup on it.

I like my jib tales about 1/3 down the luff from the head about about 20 - 25% up from the tack.


Jake Kohl
Re: Nacra 5.5sl jib block position [Re: Jake] #242087
01/05/12 11:36 AM
01/05/12 11:36 AM
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Naples, FL
waterbug_wpb Offline
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yeah, I'm still trying to figure out that luff/mast overlay thing you describe... hard to get my head around what the theory is there.

Are we setting the diamonds to match the luff curve of the sail with no downhaul, right? So that diamond tension setting would represent the minimum tension (light air setting)?



Jay

Re: Nacra 5.5sl jib block position [Re: waterbug_wpb] #242088
01/05/12 12:41 PM
01/05/12 12:41 PM
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Jake Offline
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Originally Posted by waterbug_wpb
yeah, I'm still trying to figure out that luff/mast overlay thing you describe... hard to get my head around what the theory is there.

Are we setting the diamonds to match the luff curve of the sail with no downhaul, right? So that diamond tension setting would represent the minimum tension (light air setting)?



You got me...it never made sense to me so it would be better if someone else would explain it.


Jake Kohl
Re: Nacra 5.5sl jib block position [Re: waterbug_wpb] #242097
01/05/12 07:34 PM
01/05/12 07:34 PM
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yurdle Offline
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Originally Posted by waterbug_wpb
yeah, I'm still trying to figure out that luff/mast overlay thing you describe... hard to get my head around what the theory is there.

Are we setting the diamonds to match the luff curve of the sail with no downhaul, right? So that diamond tension setting would represent the minimum tension (light air setting)?



I'm no expert (basically the opposite), but No.

If the mast is straighter than the luff curve of the sail, applying downhaul and mainsheet will bring the mast more in line with the luff curve, and the sail will get flatter and flatter, approaching only having as much pocket as is sewn into it.

When the mast is straighter than the sail it puts a little more belly and power into the sail.

If it's curved more than the sail's luff, I think you'd blow out the leech...but maybe that would just depower more.

There's also the issue of less rotation with more bend..
__

Rick White's book has quite a few chapters at the end that are basically written by a few different pros, most of which discuss their telltale placement.

I agree w/ Jake, the 5.5 (and other boomless rigs I assume) doesn't like so much tension that mast rotation gets any resistance.

Re: Nacra 5.5sl jib block position [Re: yurdle] #242099
01/05/12 08:43 PM
01/05/12 08:43 PM
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catandahalf Offline
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Andres, Aloha!

Have you put the plastic/delrin chip in the mast base?

You may check out the photos from our regatta this past Sunday on www.gulfsailing.com - note how tight the jib luff remains as the boats round the windward mark and set chutes. The trick to rig tension is to prevent headstay sag when bearing away.

Spreader rake is the key to mast bend and diamond tension, and that path takes you to the sailmaker.

Re: Nacra 5.5sl jib block position [Re: Andinista] #242103
01/05/12 11:03 PM
01/05/12 11:03 PM
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erice Offline
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for jib tell-tales you basically want a set at 1/3 height and another set at 2/3 height of the luff, about 60cm back from the luff

for rig tension probably leave you side-stays and go up 1 hole in the front stay chainplate

you do have swept spreaders right?

diamond wire tension is completely different for straight spreaders


eric e
1982 nacra 5.2 - 2158
2009 weta tri - 294
Re: Nacra 5.5sl jib block position [Re: Andinista] #242111
01/06/12 08:58 AM
01/06/12 08:58 AM
Joined: Aug 2003
Posts: 351
Santiago, Chile
Andinista Offline OP
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Andinista  Offline OP
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Bert, good pictures, thanks. I haven't lowered the mast yet. I'll move the boat for vacations by the end of the month so I'll put something on the mast base when I rig it again.

Eric, yes, swept spreaders. I have always tensioned the rig from the front but I was surprised how more effective it is to do it from the side. I found an easy way too, I'll just slide the mainsheet traveller out, fix it there somehow (tie it somewhere, easy to figure out) and use it to tighten a trap wire.

Jake and all, thanks a lot for all the advice, I got a bunch of tips and pointers to focus on, now it's time for me to study and practice. The good thing is that I realize that I know much less than I thouhgt I knew, which means new challenges and renewed interest with this change of boat.

I found these videos quite useful too:
http://www.youtube.com/watch?v=3ydpO5aPltk
http://www.youtube.com/watch?v=CZ16VSLJk1U&list
http://www.youtube.com/watch?v=aVn0gQ3bke4&list
And the other parts too, of course

Cheers!

Last edited by Andinista; 01/06/12 09:08 AM.
Re: Nacra 5.5sl jib block position [Re: Andinista] #242113
01/06/12 09:31 AM
01/06/12 09:31 AM

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Originally Posted by Andinista
I found an easy way too, I'll just slide the mainsheet traveller out, fix it there somehow (tie it somewhere, easy to figure out) and use it to tighten a trap wire.
Cheers!

On my TheMightyHobie18, i would turn the boat slightly off the wind (while on beach wheels or on the shore line), travel all the way out to one side... then crank on the main.. this would lock the boom/mast over and i could then get in my trap harness... slack the side stay and lower the pin.

Re: Nacra 5.5sl jib block position [Re: Andinista] #242114
01/06/12 09:57 AM
01/06/12 09:57 AM
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Santiago, Chile
Andinista Offline OP
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I'm a bit reluctant to do that solo. One day I'll try.

Re: Nacra 5.5sl jib block position [Re: Andinista] #242130
01/06/12 03:29 PM
01/06/12 03:29 PM
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Jake Offline
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Originally Posted by Andinista
I'm a bit reluctant to do that solo. One day I'll try.


I've done that a fair bit solo with my A-cat or F18...but I've overtensioned it that way too so I go back to the full body weight trapezing off the rear beam and it makes for a good tension I'm happy with (pulling at the rear beam gives a little more force too). As long as you keep the mainsheet with you and with a little tension on it, the traveler stays put pretty well....granted, if you're doing this with the sail, you need to watch the wind direction.


Jake Kohl
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