Author Topic: Rigging tension & mast bend  (Read 30271 times)

S/V Laelia

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Rigging tension & mast bend
« on: August 19, 2012, 03:30:40 PM »
Operating on the theory that my roller furling problems are due to sag in the forestay, I got a rigging tension gauge and put it on my backstay. I would like to be able to measure forestay tension directly but the roller furling setup with the grooved foil headstay prevents that.

When I put the gauge on the backstay, it barely registers on the gauge. Since it is a split backstay, it seems like it ought to be tensioned to about 5% of safe working load of the headstay to get to the recommended 10% of SWL on the headstay.

I understand that the headstay tension is not adjustable with the roller furling installed. Is that correct?

I sighted up the aft side of the mast and it looks to me like it bends slightly toward the stern. Is that normal? I've always thought that it should be straight both for structural reasons and sail shape. I'm reluctant to tighten up the backstays any farther and cause more bend.

Any thoughts or experience with this?

Thank you,
Ralph
On my way back to SF Bay.

Ralph Lewis
S/V Laelia, Hull 206
Somewhere between La Paz, BCS, Mexico and SF Bay

graemek

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Re: Rigging tension & mast bend
« Reply #1 on: August 20, 2012, 01:18:41 AM »
if the top of the mast is bent backwords the lower shrouds are to tight forwards,slacken the lower shrouds off first then sight up the mast,most roller furling systems are adjustable,most have a bottle screw under the drum,you might have to remove a grub screw to raise the drum to get access,
the foil on mine has about a 1 in sag in the mid point,
i moved the top of the mast forward on the bottle screw as hard as possable then tensioned the rear rigging lines up as i found this got rid of a lot of the weather helm

S/V Laelia

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Re: Rigging tension & mast bend
« Reply #2 on: August 20, 2012, 10:08:52 AM »
Since my post, I have read that some masts are built with a bit of curature at the top. I didn't see anything about it in my edition of the owner's manual - but it is pretty sketchy. Do any other owners have this bend? If so, how much should it bend.

Gramek's post makes a lot of sense about tension in the shrouds. Thanks for the tip about the roller furling adjustment.
On my way back to SF Bay.

Ralph Lewis
S/V Laelia, Hull 206
Somewhere between La Paz, BCS, Mexico and SF Bay

Dale Tanski

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Re: Rigging tension & mast bend
« Reply #3 on: August 20, 2012, 04:27:46 PM »
Ralph,

1) Forestay Adjustment - almost all furlers have an internal adjustment for tensioning the forestay.  Typically there is a internal threaded portion that allows some degree of movement without disassembly of the furler housing. Check your owners manual for the furler or the web if you are like me and don't have a manual.

2) Mast bend - your boat did not ship from the factory with any mast bend.  In boats that carry mast bend the spar is straight and bend is induced using the standing rigging.  Boats that are designed to carry any degree of bend are typically fractional rigs (the headstay only goes up 3/4's to 7/8th of the way to the masthead).  The top portion of the mast is physically tapered becoming increasingly smaller at the top allowing the sail trimmers to bend the mast primarily using the backstay.  Swept back spreaders are also another method used to induce mast bend.  The chainplate attachment points to the hull are located behind the mast base and the spreaders are pointed backward slightly to accommodate this arrangement.  As tension is applied to the shrouds, tension pulls down as well as aft to pull the masthead aft.  The reason for mast bend is the greater the mast bend the more mainsail twist along the leach.  This accomplishes several things.  In heavy air the "opening" of the leach allows air to spill and depower the rig.  In race boats the main is depowered by tensioning the backstay often with every puff to maintain proper heel and mainsail loading.  By spilling the leach it also allows the upper portion of the main to twist off.  This twist is beneficial in chop while beating to weather by minimizing turbulence when the air disconnects from the sail as the mast pivots fore and aft with every wave. The short answer is you should have no mast bend fore or aft or port to startboard on your boat.  Graemek's answer is only partially correct in that the lowers could be inducing mastbend but they also could be perfectly fine and are holding the mast nice and straight up to your spreaders and from that point on your headstay/backstay could be causing the bend.  This would be my bet.  Your headstay is too loose and to apply some tension you are over tensioning the backstay pulling the masthead aft.  By tensioning your headstay, you should minimize your headstay sag and supposed problems with your furler, while at the same time straightening up your mast.  The real question is what type of problems are you having with your furler and who made it?

Dale

"Maruska"
Pearson 365 Cutter Ketch
1976 Hull #40
Buffalo, N.Y.

S/V Laelia

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Re: Rigging tension & mast bend
« Reply #4 on: August 20, 2012, 11:26:46 PM »
Dale,

Thanks for the info. I would be surprised to find that the backstay is over tensioned. It barely registers on my tension gauge. Obviously I don't want to tighten the backstay any farther. I think what I want to do is tighten the headstay until I've got about a 5% of SWL indication on the backstay. If the mast isn't straight at that point, it is time to adjust the lowers.

The furler is a Harken 2 - as near as I can tell. I found the user's manual on the Harken site but my installation looks a bit different.



The user's manual shows a turnbuckle - as one might expect. I don't see one here. I looked inside the reel housing and I don't see an obvious way to adjust it. I'm thinking I will pull the sail off this coming weekend (if I'm not buried in the engine  :) )  and see what I find.

The problem I am having is that it is difficult to furl the sail in anything but the lightest breeze. The unit turns freely when I'm in my slip with no wind. From all I've read and been told, it is most likely because the forestay is so loose. It looks like it bows out a good 6" or more on a beam reach.
On my way back to SF Bay.

Ralph Lewis
S/V Laelia, Hull 206
Somewhere between La Paz, BCS, Mexico and SF Bay

graemek

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Re: Rigging tension & mast bend
« Reply #5 on: August 21, 2012, 02:32:32 AM »
thank you MARUSKA i know what i mean but not very good at writing it,
the nut under the drum is the adjuster,
the way i adjusted mine was to slacken of the rear wires to the top of the mast put a rope around the mast just above the spreaders and pull the mast forward till i had a lot of slack in the fore stay then loosen the nut under the drum,then remove the split pin from the connector lower down and remove the toggle,screw up the threaded part in to the drum by the sounds of it you will need to go a lot maybe 2" ..reassemble the tighten up the rear rigging then sight up the mast
forgot to ask is yours a ketch' if so don't for get the top wire will need to be adjusted

Dale Tanski

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Re: Rigging tension & mast bend
« Reply #6 on: August 21, 2012, 08:51:37 AM »
Ralph,

Why all the toggles????  Can't imagine that the drum would interfere with the pullpit if it was lower.  Perhaps who ever installed the furler measured incorrectly and cut the forestay a bit short, thus the toggles.  Maybe you just need to remove one of those to shorten your forestay.  Each toggle is also a possible fitting to fail down the road. 

The threaded portion under your furler is indeed the adjustment as Graemek has explained.  It is not a turnbuckle rather a one screw adjustment. Screw it in to shorten and out to lengthen.  Be very careful to leave enough threads screwed into the furler so they do not part company.  Theoretically you would be screwing the parts together, but if you choose to remove a toggle you may need to extend slightly.

Graemek also brought up a good point, your backstay (while the boat is at rest and not loaded) may not be carring the load.  It could be your triasic stay (mast to mast) and your mizzen backstays. 

I would recommend that you loosen what you need to loosen to get you mast straight fore and aft.  Then determine how loose your forestay actually is.  Shorten the forestay preferably by removing a toggle or two, and then tighten the main mast backstay to achieve the desired headstay tension.  Sight the mast to make sure it is still straight, if not repeat the procedure. Once the main is straight and true, then you would adjust your mizzen so it is parallel with the main.  You don't need to measure the parallelism with a ruler, just eyeball the rigs from a nearby dock.  If it looks parallel it probably is. 

As far as headstay tension, this one is a tricky subject.  As a rule of thumb, I tension my headstay with the sail installed so that at the dock there is not any noticeable sag.  You can deflect it slightly when it bounces if you push and pull aggressively but all in all it looks straight to the eye while rolled and unloaded. 

You could also do the math by using your mizzen halyard.  Measure the vertical height of the mizzen mast from a horizontal line extending from the butt of the main mast and then the distance from mast to mast along the cabin top and calculate the hypotenuse.  Then use the halyard to hoist a tape measure and adjust the mizzen mast rake to the correct hypotenuse number. The eyeball method is all we use.

One other thought came to mind.  Even though your backstay is split and the load on each lower leg is 50% of the total load, the lower wire size is smaller than the upper section of backstay because it only has to carry 50% of the load.  So make sure you take the wire diameter into account with your tension gage if you go that route.

I would agree, the most typical reason a roller furler is resistant to rolling is insufficient forestay tension.

Dale
"Maruska"
Pearson 365 Cutter Ketch
1976 Hull #40
Buffalo, N.Y.

S/V Laelia

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Re: Rigging tension & mast bend
« Reply #7 on: August 21, 2012, 09:55:58 AM »
Thank you both for the information and ideas.

The reason for all the toggles is that they were there when I bought the boat. I've been scratching my head ever since over the reason for them. Given the amount of bend in the mast, it seems to me that one of the lower toggles could come out. I will see if that works.

In any event, the headstay (and the rest of the standing rigging) is all going to be replaced before I head south. The previous owners had the boat for 15 years and had never replaced it. The surveyor recommended replacement every 7 years for boats operating from Sausalito because of the frequent fresh breezes and rigging vibration, etc.

Which brings to mind another question. When I am in my slip and there is more than about 5 knots wind from some directions, the whole boat vibrates. I have been standing next to tne mizzen when this happened and the mizzen mast is at least part of the reason - it vibrates like a clarinet reed. Do your boats do that or is it yet another sign of poor rigging setup?
On my way back to SF Bay.

Ralph Lewis
S/V Laelia, Hull 206
Somewhere between La Paz, BCS, Mexico and SF Bay

graemek

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Re: Rigging tension & mast bend
« Reply #8 on: August 21, 2012, 10:50:33 AM »
yes mine vibrates as well don't know if this is good or bad I'll await some brains to answer that one

slokat

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Re: Rigging tension & mast bend
« Reply #9 on: August 21, 2012, 12:16:46 PM »
I would bet that the two lower toggles shouldn't be there, whoever worked on that setup didn't loosen the backstays enough (including the Mizzen backstays) to be able to connect the top shackle to the tang.

Dale Tanski

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Re: Rigging tension & mast bend
« Reply #10 on: August 21, 2012, 12:42:42 PM »
Ralph,

Mizzen oscillation - Two years ago my mizzen hardly went into the dance.  If it did, the wind was well into the 20's.  Last year it seemed to dance more often, again from say around 15 and up.  This year nothing!  Keep in mind because I take my boat home every year I have to drop the rigs, so every year the are "re-tuned" so to speak.  For the heck of it, I will throw our Loos gage from the J-22 on the shrouds and see what they are set at.

Do you hang your main boom of off the short section of cable from the mizzen mast to support it?  I hang mine off of the topping lift figuring it was redundant, but last year I began to wonder if hanging it on the short cable would stabilize the mizzen.  Perhaps that is what that short cable was designed to do.

Dale
"Maruska"
Pearson 365 Cutter Ketch
1976 Hull #40
Buffalo, N.Y.

S/V Deo Volente

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Re: Rigging tension & mast bend
« Reply #11 on: August 21, 2012, 09:42:01 PM »
I would bet that the two lower toggles shouldn't be there, whoever worked on that setup didn't loosen the backstays enough (including the Mizzen backstays) to be able to connect the top shackle to the tang.
I would bet this is the case, it can be difficult pulling the furler straight to connect it. I still have the old Stearns Dynafurl which isn't adjustable. I release the backstay to connect mine, it's easier since I added a solent stay some years ago, it enables me to tilt the mast forward while making the connection.
Does your sail go to the top of the headstay? The swivel needs to be close to the top to work.
"S/V Deo Volente"
Pearson 365 Pilothouse
Hull #17 1980
Duluth Minnesota
Bob

S/V Laelia

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Re: Rigging tension & mast bend
« Reply #12 on: August 21, 2012, 10:34:22 PM »
My mizzen doesn't have a cable to hold up the main. I'll bet that what that mysterious tang a little over half way to the spreaders is for. I use the main topping lift. The extra cable does seem redundant. What I would really like is a boom gallows but it isn't real high on my priority list.

It doesn't seem like the vibration would be a good thing. Vibration causes extra stress at all of the attachment points. I think I will set the mizzen lowers and shrouds a bit tighter when I retune the rigging.

---

If they had to put on two toggles to make up the slack, I would say it was a very bad measuring job - or the main is raked farther back than I think - or some of both. We will see.
On my way back to SF Bay.

Ralph Lewis
S/V Laelia, Hull 206
Somewhere between La Paz, BCS, Mexico and SF Bay

S/V Laelia

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Re: Rigging tension & mast bend
« Reply #13 on: September 22, 2012, 09:29:35 PM »
I got my new headstay in place and adjusted the tension to a little over 10% SWL. I spent the better part of two days wrestling with the Norseman fittings. After rereading the instructions for the hundredth time I realized that I was only supposed to unlay the outer 12 strands of my 1x19 wire. The cone goes over remaining 7 strands. After that, it was about 30/fitting counting the time to cut the wire, put on the fitting, unscrew it and fill it with Boatcaulk and put it back together. The stay is just barely long enough. I had to do some juggling of headstay and backstay tension to be able to tighten up the rigging screw far enough to put cotter pins in place. Now the mast is very nearly straight and the tension is in the range I was aiming for.

Unfortunately, the boat now vibrates worse than before when I am sitting at the dock with a light beam wind. I can feel it and see it in the main mast as well as the mizzen. It is a fore and aft pumping motion. When I'm below deck, it is like living in a giant bass violin. I've read several articles on-line that say it is not an unusual thing to happen. It has to do with air flow separation around the mast and rigging and also the natural resonant frequency of the masts and rigging, Karman effect, etc, etc, blah, blah. I just want it to stop.

The first step recommended is to tighten the lower stays, then the shrouds. It is not guaranteed to work. There are a bunch of other things people have done that worked for their particular situation. Do an online search for "mast vibration" if you want more ideas.

It looks like there is no shortage of ideas about how to fix it. It needs fixing - the whole boat vibrates and it gets loud enough to get really annoying.
On my way back to SF Bay.

Ralph Lewis
S/V Laelia, Hull 206
Somewhere between La Paz, BCS, Mexico and SF Bay

graemek

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Re: Rigging tension & mast bend
« Reply #14 on: September 23, 2012, 01:56:54 AM »
had the same thing,I cured mine by tighteng up the lower rear stays and loosening the front stays a little,not by the book but it worked