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Old 25-02-2006, 19:13   #1
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Mast Bend

HELP! I have a little dilema with my main mast. It has this lovely S shape to it. I have played around with all sorts of scenarios to try and get the thing right.
I may have to take a photo, but I will try and describe this as closely as I can.
Rig is Ketch. Main mast is deck stepped.
The mast shape has a slight positive bend in the lower area of the mast and what I would consider to be just right. This bend is controlled by the inner stays. of course. From the top of where those stays attach to the mast, the mast takes a negative bend.
I have a small amount of aft rake. Adjusting rake from straight up and down to an extreme rake angle makes no difference. So I have taken it back to where all my reading and studying has suggested a good angle of rake. This is where I think the issue lies. I maybe wrong, so suggestions are all welcome. At the mast head, the forestay attaches to the mast cap about 6" out and about 2-3" higher than the head. (Is head the right word?) The twin aft stays attach to the head almost right at the mast say an 1" out and are 3"-4" below the terminal height of the forestay. So as I tension the aft stays, I think the forestay levers the mast out of align creating this bend. Do you think I am on the right track??
So I decided to try a little adjuster today to see if I am on the right track. I extended the aft stay terminals out. I could not raise the hight, but I did take them 4" out from the original terminal position. I thesion everything up and to much disgust, nothing changed. Now that maybe because I am simply not getting the terminals out far enough and level enough. I can make a better attachment this week when I have time. But what are thoughts here?
Now I have had all sorts of people comment, but none are pro's. One comment was a babystay to pull the mast forward. But I have big issues with my Genoa getting wraped around the shrouds now, without more stays in the road.
But one recent comment was, I may have to fit a "Diamond stay". Can someone, anyone, tell me what is a Diamond stay, where is it attached and will it get annoying and is this the right approach and and and....
Thanks all,
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Old 25-02-2006, 19:19   #2
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Is there any possibility you have the rig too tight?
At the very least, you may want to start by backing off all of the rigging and re-tensioning the whole rig. Also, do you have a triadic between your main and mizzen? this can also help adjust the upper half of the main mast.
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Old 25-02-2006, 19:28   #3
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Yes it is possible it's too tight. I have wondered that. But I have had issues with the furling headsail being too loose and pumping. So one guy said I needed to make it much tighter.
Yes there is a Triadic, but the aft stays on the mizzen are running stays, controlled by 4:1 purchase set of blocks and I simply don't have the purchase to tighten these by hand. They are running stays so as in theory, I can let the mizzen right out. But then in practice, I have found I don't really need to let it out. I simply leave it to self tack fairly well centre and pull it down when wind is behind us.
Sooooo, should I make the Mizzen aft stays more permanent and tension them more. I could imagine tension on the Triadic would certainly solve the issue. At the moment, there is almost no tension on it, it hangs limp, cause I can't get the tension on the mizzen stays.
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Old 25-02-2006, 19:35   #4
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I am no fan of running backs, but they do serve thier purpose. Although making the backstays permenant and adding tension will probably solve the symptom, but will definitely not be the cure. Start with releasing all tension on the rig, and if you do not have a rigging scale, get one. It is a worthwhile investment. I am not sure about ferro, but wood boats require less tension than fiberglass boats, and over tensioning has caused quite a few leaks over the years.
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Old 25-02-2006, 19:37   #5
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So how does a rigging scale work?
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Old 25-02-2006, 19:39   #6
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I should have added, And what's the cost ruffly.
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Old 25-02-2006, 19:47   #7
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West Marine says....$179.99 for the big one. This will handle up to 3/8" wire. There are bigger scales out there, but I am not sure of the source. Never needed any bigger. They usually come with a chart that shows breaking strength of each wire size, and Toss's book will tell you the proper tension. If I remember right, shrouds are 20% standard, and the forestay is 25-30%, but verify that. It has been about a year since I have done any major rigging. The forestay should bend a bit under load, and on some rigs it seems like too muc, but that is just the nature of the design.
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Old 25-02-2006, 20:53   #8
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Hmmm, 3/8 would be too small for me. I am running 1/2". Forstay is SST and the rest is Galv. The only stays that would be 3/8 are the inners.
I will have to ask around and see if anyone will lend me something. That is just tooo expensive. It equates to about NZ$300 for me.
Thanks for the help though. I am thinking more about the Mizzen stays and finding a better way to tension them. Maybe I will make them permanent instead of running. This will allow me to tension that Triadic which I think will solve the Main Mast issue.
I also think I need to fit chain plates for the Mizzen backstays. At present, the stays attach to the aft samson posts. So they sit each side, a good foot or more inside the boat. Fitting Chain plates will allow me to get the stays outside the hull. Thus it will also allow me to get just a little more tack on that mizzen sail before the sail is against the stays.
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Old 25-02-2006, 21:12   #9
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Rigging stuff is a bit pricy if you don't use it much, but I have changed the gang on several of my boats, so it made sense for me. For your purpose, it might be cost effective to hire a rigger to come tune the rig. It shouldn't cost much, and once it's done, it is not something you have to so very often on a cruising boat.
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Old 25-02-2006, 21:27   #10
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Rigging

Okay here goes. May not be applicable but: Assuming this is a mast head rig, You need four wyres going to the top of the mast and four wyres going to the spreader. The wyres going to the top come from the pointy ends and to the sides either opposite or just aft of the mast. Two lowers go about 2 or 3 feet forward of the uppers and two go the same distance aft. If you only have two lowers attached next to the upper shrouds on the deck the mast may pump. You fix that with a baby stay at spreader height on the mast and 3 feet or more forward of the mast on the deck. Good idea to have aft lowers if you do this. You do not need running backstays with a mast head rig, unless you put on an inner forestay for a stay sail. Your mast section will determine if you need running back stays. When tightening the rig make the mast stand almost vertical using a level and then move the top back about 4 inches, maybe six. Rake is a nebulous concept that some folks think is a good idea. Don't listen. Tighten the forestay and backstay to the appropriate amount. Check with the rigging shop for the correct tension. Tighten the upper shrouds, make sure they have the same tension. The center of the mast will bend away from the upper shroud that is too tight. Tighten the uppers to the correct tension. The mast should be straight. It may bend a bit forward in the middle due to its years of service. Tighten the forward lowers a bit tighter than the aft lowers. The forward lowers have less tension than the uppers. With the lowers snug you may have a teansy bit more forward bend in the mast. One or two inches is enough. If you do not induce a small bend then you will be just trying to drive the mast through the boat. A mast that is held captive with rigging that is too tight, and kept in a straight line is trying to buckle, as in break a few feet above the spreaders. Do not look at the mast while sailing, it is never pretty.
Let me know if you have multiple spreaders or a fractional rig or whatever.
A diamond stay is to support a piece of mast that is free standing, like the top of a fractional rig. They use a diamond strut to to the top bending back and sometimes to stop the top falling off ( bending to leward ) Some boats alow this to happen to spill wind.
Michael
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Old 26-02-2006, 03:16   #11
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http://www.loosco.com/index2.htm

How To Use Tension Gauges (Loos & Co. Inc.)
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i don't know what tension gauge you'd use on larger wire sizes (over 3/8").

FWIW:
Sorry, donít know where I copied the following advice from.

First, you'll probably need 2 tuning gauges, because the shrouds and stays are diverse in size.
Next, make sure your spreaders are angled to bisect the angle created when the shrouds pass through the retainers atthe ends. This will not be level to the deck. (My understanding is thata primary reason for rig failure is collapse of a spreader).
Then, starting with the main mast, adjust the lower shrouds to make the mast perpendicular to the deck. Don't tune yet, just make the shrouds taut.
Do the same to the mizzen. Adjust the forestay to keep the mast nearly vertical (there will be maybe 5 degrees rake aft when you're done tuning).
Adjust the main backstays (probably split) so that they are taut, not yet tuned.
Then, adjust the upper shrouds, first on the main, then the mizzen, so they are taut, and so they do not bend the mast, as observed by sighting up each mast from deck level. Check the recommended loading to be tuned according to the Loos instructions.
Tune each lower shroud gradually, working around several times, something like
tightening the bolts on a head gasket.
When you have achieved the proper loading, Do the same to the uppers and stays, working around several times. Keep checking that the mast is straight by observing from deck level.
Take an occasional peek at the triatic, if you have one. It shouldn't be holding too much. If it get's too tight, it's possible to fail a lower aft mizzen shroud, or bend one of the masts. When you are satisfied that all shrouds and stays except the triatic are properly loaded, and everything is in alignment, including the aforementioned spreaders, then you can tune the triatic stay to hand-tight, not anything more. Don't try to tune the triatic to a working load recommendation.
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Old 26-02-2006, 09:42   #12
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Very clear and consice GORD. One other general rule of thumb, if tuning without a scale, the leeward shrouds should be just tight enough not to be slack while underway, and no tighter. I will take a photo of the scale in a while and post it to show haw it works.
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Old 26-02-2006, 09:57   #13
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OK, here it is. The lower wheels put a bend in the wire, and the upper indicater shows how much force it took to put a bend in the wire. There is a scale posted on the tool that translates this into percentage of breaking strength.
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Old 26-02-2006, 11:21   #14
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Scale

There is also a cheaper version made by Loos. It needs to be attached each time you take a reading and you pull a line.
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Old 26-02-2006, 11:33   #15
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If you do loosen your rigging, check to see that your mast is straight while free-standing.

If it's bent to start with, especially between the shroud connections, you'll never get it straight without de-masting and having it straightened.

A bent rig will just get worse under tension....................._/)
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