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mast pre bend #160632
11/17/08 05:40 PM
11/17/08 05:40 PM
Joined: Nov 2008
Posts: 6
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ready Offline OP
stranger
ready  Offline OP
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g'day im jerry first time user sail A CLASS MK4 at kingston s.e south australia water is generally flat average wind varies between 10kts to 20kts .could anyone advise me on mast set up as im still playing around with prebend and chain plate settings . cheers jerry


Jerry
A class sail no. 763
mk.4
-- Have You Seen This? --
Re: mast pre bend [Re: ready] #161029
11/20/08 11:11 PM
11/20/08 11:11 PM

C
cattail
Unregistered
cattail
Unregistered
C



Hi Jerry, I also have a Mk IV and other than the downhaul adjustment I have not changed anything on the diamond wire setup. On windy days the mast will start to slap from side to side after hoisting the sail easing the downhaul until launch keeps that to a minimum. Have you asked the guys over at www.ahpc.com.au yet? It might be a local call for you and Im sure they will know the answer. Keep intouch I'm learning more about cats on this site than anywhere else. Great group here!

Re: mast pre bend [Re: ] #161099
11/21/08 05:46 PM
11/21/08 05:46 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
Carpal Tunnel
Jake  Offline
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South Carolina
Jerry,

I've got a decent light air setup on my boat and as soon as I get a chance to extract my notebook from the trailer, I'll list them here.

Jake


Jake Kohl
Re: mast pre bend [Re: Jake] #161102
11/21/08 06:01 PM
11/21/08 06:01 PM
Joined: Sep 2002
Posts: 3,224
Roanoke Island ,N.C.
Team_Cat_Fever Offline
Carpal Tunnel
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Roanoke Island ,N.C.
Originally Posted by Jake
Jerry,

I've got a decent light air setup on my boat and as soon as I get a chance to extract my notebook from the trailer, I'll list them here.

Jake


Sure ya will, I've heard that before.


"I said, now, I said ,pay attention boy!"

The cure for anything is salt water - sweat, tears, or the sea
Isak Dinesen
If a man is to be obsessed by something.... I suppose a boat is as good as anything... perhaps a bit better than most.
E. B. White
Re: mast pre bend [Re: ] #161619
11/30/08 05:16 AM
11/30/08 05:16 AM
Joined: Nov 2008
Posts: 6
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ready Offline OP
stranger
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thanks every one for replying to my to my questions .sorry about the delay at getting back to you.any imformation on mast rake ,pre bend ,or general set up's is appreciated.


thanks ready


Jerry
A class sail no. 763
mk.4
Re: mast pre bend [Re: ready] #161621
11/30/08 09:23 AM
11/30/08 09:23 AM
Joined: Jun 2001
Posts: 1,911
South Florida & the Keys
arbo06 Offline
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Rake in general, less wind, set up stright, more wind, more rake. As far as prebend goes, I think you will need info from the manufacturer or other owners.


Eric Arbogast
ARC 2101
Miami Yacht Club
Re: mast pre bend [Re: ready] #161624
11/30/08 11:50 AM
11/30/08 11:50 AM
Joined: Jan 2004
Posts: 196
Arkansas, USA
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CaptainKirt Offline
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Arkansas, USA
Jerry-
I'm sure you'll love the "A" cat! Very hard to give specifics on these boats as the masts can be different (the older Mk IV's even had aluminum masts though most have upgraded to CF- but could be Saarberg, Hall, Fiberfoam, etc. CF mast) and the sails can be very different materials (Dacron, Pentex, etc.) built by different sailmakers (Goodall, Ashby, Danger, Landenberger, Glaser, Ullman, etc.). Best thing to do in your particular case is to note type of mast (if possible), year of boat (if can't ID mast will at least give a clue), sailmaker and year of sail (if possible) and E-mail the sailmaker for suggestions as to prebend, rake, spreader length, etc.

Enjoy!

Kirt


Kirt Simmons
Taipan, Flyer
Re: mast pre bend [Re: CaptainKirt] #161650
12/01/08 09:37 AM
12/01/08 09:37 AM
Joined: Nov 2008
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AUS Offline
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Posts: 29
Jerry,
You are in the right place. Call either Glenn at Ashby Sailcraft or Greg at Australian High performance. Both are very intimate with all of the Boyer and Flyer A cat designs. They will be able to give you basic mast set ups and give you a base rake setting.

Re: mast pre bend [Re: AUS] #162251
12/08/08 05:22 PM
12/08/08 05:22 PM
Joined: Nov 2008
Posts: 6
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ready Offline OP
stranger
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thanks guys ill get in touch with boyer or glen ashby
and then start to set things up


Jerry
A class sail no. 763
mk.4
Re: mast pre bend [Re: ready] #162300
12/09/08 07:58 AM
12/09/08 07:58 AM
Joined: Nov 2005
Posts: 246
Kiel, Germany
Baltic Offline
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Baltic  Offline
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Posts: 246
Kiel, Germany
Could you leave a post when you have received reply from Glenn? I mailed him about one week ago with a similar question but haven't received any reply yet. May be my message is stuck in his spam-filter ...

However, I would like to understand the subject in general. Right now, I have an average spreader rake but pretty high diamond tension. I guess, I can achieve the same mast bend with higher spreader rake and less tension on the diamonds. How will this affect the performance of the boat, is one option preferable over the other? If somebody could give me advice on this ...


F18: C2 / A-Cat: Minelli
Re: mast pre bend [Re: Baltic] #162302
12/09/08 08:20 AM
12/09/08 08:20 AM
Joined: Apr 2008
Posts: 921
Alachua, FL
Mugrace72 Offline
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Posts: 921
Alachua, FL
Originally Posted by Baltic


However, I would like to understand the subject in general. Right now, I have an average spreader rake but pretty high diamond tension. I guess, I can achieve the same mast bend with higher spreader rake and less tension on the diamonds. How will this affect the performance of the boat, is one option preferable over the other? If somebody could give me advice on this ...


Me too.

How much pre-bend is too much? This thread is about A-Cat stuff but I think the concept is universal.

I have a new main for my H20 and using Mike Krantz's technique of matching the mast bend to the sail luff curve, I was able to make a perfect match.

However, to do that I ended up with 4" of spreader rake and 800# wire tension.

I can find no reference in the various tuning manuals and posts of anyone using more than 2 1/2" of rake. Have I gone too far?

The sail looks great (we will find out this weekend).


Jack Woehrle
Hobie Wave #100, Tiger Shark III
HCA-NA 5022-1
USSailing 654799E
Alachua FL/Put-In-Bay
Re: mast pre bend [Re: Mugrace72] #162315
12/09/08 09:49 AM
12/09/08 09:49 AM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
Carpal Tunnel
Jake  Offline
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Posts: 12,310
South Carolina
Spreader rake will change how your mast reacts to pressures from wind and control lines. More rake will turn loads into mast bend faster than less rake will. Loads include side forces from wind, compression from trapezing weight (additional leverage), downhaul, and mainsheet tension.

I still treat spreader rake as a method to fine tune the mast reaction based on the weight of the sailors on board. Heavy sailors will want the mast to bend less quickly in response to additional pressure (higher wind) so they will want less spreader rake.

My impression of this is changing a little through conversation with some of the a-cat guys but I haven't completely digested what they're doing with tuning spreader rake.


Jake Kohl
Re: mast pre bend [Re: Jake] #162356
12/10/08 12:57 AM
12/10/08 12:57 AM

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cattail
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cattail
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Mast bend is fine tuned with the Cunningham right? I thought the prebend would only be re-set for a sail change. Watching the racing cats video the sail shape changed a lot as the mast came back the sail got fuller there was a mainsheet trim with every Cunningham adjustment. Have to watch that one again I believe it was a Tornado used in the video they covered rake of the spreaders as well. From my limited experiance on the MK IV every adjustment on the water results in a slowdown before speed increases. I was told by another Boyer owner to set the rake using the trap line as a ruler it should be about the same at the back crossbrace and at the forestays you can adjust for heavy or lite wind only on the beach.

Re: mast pre bend [Re: ] #162361
12/10/08 03:52 AM
12/10/08 03:52 AM
Joined: Nov 2005
Posts: 246
Kiel, Germany
Baltic Offline
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Posts: 246
Kiel, Germany
Jack, you're talking of Mike Krantz's technique - is there a document or a link you can provide? And Jake, do I understand you right that less crew weight results in higher spreader rake and vice versa?
I have to re-adjust all parameters (spreader-rake, diamond tension, mast-rake, and side stay tension) since I put a pretty recent sail (Ashby 2004) on my A-Kat from 1997. There are so many parameters to gamble with - where to start? With the current set-up I have the feeling that my boat is too sensitive to gusts.


F18: C2 / A-Cat: Minelli
Re: mast pre bend [Re: Baltic] #162386
12/10/08 11:07 AM
12/10/08 11:07 AM
Joined: Apr 2008
Posts: 921
Alachua, FL
Mugrace72 Offline
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Mugrace72  Offline
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Alachua, FL
Originally Posted by Baltic
Jack, you're talking of Mike Krantz's technique - is there a document or a link you can provide?


A few years back, Mitch Booth showed Dave and I how to tune our Tiger mast to match the luff curve of the main. He had us flip the boat on it's side, connect the main on the halyard hook, connect the downhaul, and mainsheet and sheet in hard as though you were going up wind. Note - the main is not in the luff track, it is outside the mast. Look at the luff curve of the sail, and compare it to the curve of the mast track. Adjust your diamonds and spreader rake accordingly to get them to match. That is your new "base setting". We found that we were carrying anywhere from 800 to 1,000 lbs of diamond tension to get some mainsails dialed in.

Mike Krantz quote




Jack Woehrle
Hobie Wave #100, Tiger Shark III
HCA-NA 5022-1
USSailing 654799E
Alachua FL/Put-In-Bay
Re: mast pre bend [Re: Mugrace72] #162437
12/11/08 02:41 AM
12/11/08 02:41 AM
Joined: Nov 2005
Posts: 246
Kiel, Germany
Baltic Offline
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Baltic  Offline
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Posts: 246
Kiel, Germany
... do I understand this right: 800 - 1000lbs diamond tension? This converts to 360 - 450 kg - this is enormously much! Currently I have 270kg (= 600lbs) and feel already uncomfortably with it. But again, with more spreader rake and less tension I should be able to achieve the same results ...


F18: C2 / A-Cat: Minelli
Re: mast pre bend [Re: Baltic] #162438
12/11/08 02:51 AM
12/11/08 02:51 AM
Joined: Nov 2005
Posts: 246
Kiel, Germany
Baltic Offline
enthusiast
Baltic  Offline
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Joined: Nov 2005
Posts: 246
Kiel, Germany
Jack, you tuned your mast according to Mike Kratz's technique and want to make a try upcoming weekend? Please let me know how it has worked!


F18: C2 / A-Cat: Minelli
Re: mast pre bend [Re: Baltic] #162440
12/11/08 03:57 AM
12/11/08 03:57 AM
Joined: Jun 2002
Posts: 1,658
Florida Suncoast, Dunedin Caus...
catman Offline
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Florida Suncoast, Dunedin Caus...
We found that we were carrying anywhere from 800 to 1,000 lbs of diamond tension to get some mainsails dialed in.


Seems to me if it takes that much to make it happen you might want to look at having the sail re-cut.


Have Fun
Re: mast pre bend [Re: Mugrace72] #162443
12/11/08 06:21 AM
12/11/08 06:21 AM
Joined: Nov 2005
Posts: 1,203
uk
TEAMVMG Offline
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TEAMVMG  Offline
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Posts: 1,203
uk
Originally Posted by Mugrace72
Originally Posted by Baltic
Jack, you're talking of Mike Krantz's technique - is there a document or a link you can provide?


A few years back, Mitch Booth showed Dave and I how to tune our Tiger mast to match the luff curve of the main. He had us flip the boat on it's side, connect the main on the halyard hook, connect the downhaul, and mainsheet and sheet in hard as though you were going up wind. Note - the main is not in the luff track, it is outside the mast. Look at the luff curve of the sail, and compare it to the curve of the mast track. Adjust your diamonds and spreader rake accordingly to get them to match. That is your new "base setting". We found that we were carrying anywhere from 800 to 1,000 lbs of diamond tension to get some mainsails dialed in.

Mike Krantz quote



i think that you have mis-understood what the boss was saying. That curve is the MAX mast bend that you want with full down-haul, you just need enough prebend to allow the downhaul to get you to this point.



Last edited by TEAMVMG; 12/11/08 06:22 AM.

Paul

teamvmg.weebly.com
Re: mast pre bend [Re: TEAMVMG] #162447
12/11/08 09:31 AM
12/11/08 09:31 AM

A
andrewscott
Unregistered
andrewscott
Unregistered
A



Question:
If you "overset" your pre-bend so when you max downhauled... you went past "fully flat" ... would that put more draft in your sail and power you up?

Last edited by andrewscott; 12/11/08 09:32 AM.
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