SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Dynamic tuning of rig

16K views 106 replies 26 participants last post by  casey1999 
#1 ·
DougSeabag mentioned that a major lesson he learned from his last boat was the importance of dynamic tuning of the rig.

Welcome back Doug
"2. Tune your rig. :) What I had no knowledge of was that it HAS to be "dynamically tuned". When we stepped our main mast about 10 months before we headed East, without having dynamically tuned it after that, in effect, I did a lot more damage to our boat than if I hadn't stepped it at all.

We had 2 completely different rigger "companies" providing our out and in needs, but neither one mentioned the need to dynamically tune the rig.
One rigger was from West Marine, and the other was the best one in Fort Lauderdale: Nance & Underwood. Both had / have decades of experience and seemed to know their stuff. Which I still don't question; but, perhaps I didn't ask the right question, or something, but now I know, and am therefore sharing the mantra: Dynamically tune your rig."


The way I understand it dynamic tuning is done under sail in varying conditions. If so at $100 per hour this could easily cost one or two thousand dollars. I believe most sailors even racers do their own dynamic tuning.

Doug I would like to hear from you on this subject. Specifically why you now see this as so important and if you believe you could have done it yourself or would you get professional help?

Who dynamically tunes their rig? How do they do it and how important is it?
 
See less See more
#42 ·
Ohhhh, OK, yes, now that I see this, we did have those. Nevertheless, will these really absorb all the wrenching, for and aft, (pumping), if your mast is not tuned well enough?

According to the "rigging experts" who have listened to our story, that pumping action is what caused the metal fatigue which broke 2 chainplates at their tabs, just above the ribs, and just under the decking.

It is rather frustrating that some "experts" will provide a very reasonable explantion that fits with all the history and facts, and then some experts seem to be in denial of that, and point to pitting and corrosion as the culprit.

I feel more like I am in a room full of lawyers than reasonable men. :)
 
#38 ·
"Casey.... this was what I did not do after the main mast stepping 10 months prior to my rig "failure":
"Then you take the boat for a sail in a stiff wind and basically tune the rig so that the lee shrouds do not go slack..."

Assuming that the lee (downwind) shrouds / stays do go slack, and you adjust those to be, oh lets say 65 lbs of tension, then wouldn't the mast be bent toward that recently adjusted side when you come about?

Or how do you do this dynamic tuning, without pulling the mast to one side or the other, if you're adjusting it while she is heeled over?

Please pardon my ignorance, but what the hell, I am ignorant. :)"


Take half of the slack from lee shrouds, tack and tension the new lee shrouds as much as the old ones.
 
#39 ·
Dynamic tuning – Yes you need to make sure both sides have equal tension. If not, your mast will no longer be in column (not good!) and, you will be slower on one tack than the other. I use my Loos gauge to check for equal tension. You can do this without a gauge by counting the number of new turns you are putting on the turnbuckle and doing the same to the other side after you tack. Properly tuned, your wire shouldn’t stretch for a very long time so dynamic tuning is something done very infrequently like after a re-wiring. I actually have two sets of tune, one for light days and the other for our (normal) heavy air days. A boat tuned for heavy air will be a little too stiff and not perform as well on light days. Probably more important for the racer types than the cruisers. On a mast head rigged boat, the backstay adjuster pulls out the stretch in the headstay, stiffening up the boat and causing it to heel less. Next time you are sailing in heavy air site your headstay along the mast. If you see it bowing out to leeward, chances are you need to tighten headstay tension or would benefit from a backstay adjuster. On fractional rigged boats, you are pulling a curve into the mast using the headstay as a fulcrum. This reshapes the main.
 
#44 ·
So if conventional tuning (and cable sizing) depends on the leeward side going slack, and that constnatly cycles the load causing cyclic stressing which in turn weakens the cables...

Does that mean it would be better for the working life of the shrouds, to spec shroud cables that could be tensioned down enough so that the leeward side never went slack? Keeping a uniform tension, or a more uniform tension, on the shrouds all the time?
 
#45 ·
I would tend to agree with this statement. Even the Loos gage manual previously posted tends to contridict itself. On one hand it says if a lee shroud goes slack (0 lbs load) then the strength of mast and spreader is reduced by factor of 2, yet the tight tension diagram shows 0 lbs on the lee shroud, I would think you would want say 5% load.

I have in fact measured my lee shroud while sailing in a stiff wind and I do infact have 5% load on the lee shroud and 8% on windward.
 
#47 ·
My exposure to conditions like these are limited to one week in a Farr 395 with a full crew.
The wear and tear on the boat is impossible to explain. It sounded like someone was beating the hull with a sledge hammer. You could hear the fiberglass crack like it was being destroyed in a giant grinding machine.
The idea that any part could sustain loads that would damage it is very understandable.
The chain-plate however is the last part that should fail. The tangs, swages or wire, turnbuckles, pins even cotter rings I could see failing first by design.
The chain plates should be strong enough that they do not flex under any normal condition to suffer any fatigue.
I have had a few off forum communications with Doug and consider him a friend.
If he is going to do this again, which is is planning I think this is an important enough subject look at carefully.
If the failure of the Gulfstar rig was 99 percent warn out chain-plates and 1 percent rig tuning that will affect his and many others decision making.

As usual I'm open to learning new stuff.
 
#49 ·
I am not capable of tuning under sail simply because I need to keep my hands on the wheel and would probably lose the tensioner over the side, but I do try and balance the rib dockside. My problem is trying to tension the forestay as it has the self furling covering the stay and therefore I cannot connect the tensioner directly. Is there a solution to this?
 
#50 ·
I put boat on auto helm and measure tension. Have a line around my wrist and attached to the Loos gage- cannot loser overboard. As the Loos instructions say, you cannot measure forestay tension if you have a roll furler- you need to measure backstay tension and then you can use trig to calculate forestay tension based on the angle of the forestay and back stay.
 
#51 ·
Then I wonder why in the V70 race a month or so ago, when one of the boats lost a mast, they took off, had to return, along with a quote, that it usually take 2-3 days of sailing as a full crew to tension things correctly! here we as cruisers, some of us as evening/weekend warrior racers trying to set the rigs up in an afternoon? sailing by ourselves? think we will succeed! doubt it. This is a constant you must always do! adjust some, keep a log, adjust some more, see if it works better,by gaining speed, degrees upwind etc.

Along with taking multiple measurements with a "STEEL" tape as usually recomended, as it will not stretch like the typical cloth/plastic tapes will that are long enough for most of our mast hts, ie a 50-100' tape is usually needed.

Then "ONCE" you figure out the where you need to be, you keep it there. Along with figuring out how tight to tighten the backstay, if you have an adjustable mini forestay, I have the mini, not adjustable, you can tweek the tune with either or both. Locally, folks do these adjusts thru out the race, tension back stay upwind, loosen down winds. Same with clew on main, halyard adjusting, boom vang etc.

Marty
 
#54 · (Edited)
I am not sure how the OP meant the term 'dynamic tuning' or if he meant it as a specific form of tuning. My guess is that the intent of the phrase is simply to suggest that you cannot tell whether a rig is properly tuned until you see it loaded under sail.

When I worked with the rigging crew at Derecktors years ago, we would typically measure the rake of the mast before removing the spar. We would also count the threads on the stays. If we we were replacing a stay, we would take measurements of the old stay with the turnbuckle adjusted to the exposed threads count, and with the stay stretched to a specific tension.

All new rigging stretches after being initially put into service. We had a chart which was used to calculate the expected initial stretch, and the new stay was constructed shorter by the amount of anticipated initial stretch. My assumption regarding the VOR70's needing 3 days for tuning is that these are complex rigs, but I also assume that this is so the shrouds can be stretched and re-tuned.

When we restepped the mast, we would set the shrouds loosely with the mast centered, and then set the fore and backstay to the previously measured tensions and the previously measured rake.

From there we re-centered the masthead, and the centered the shrouds so that the mast track sighted straight athwartships and the tensions matched from side to side. As a broad generality, the cap shrouds had the highest tensions, with shroud tensions reducing as you moved down the mast.

Once set up, if any of the shrouds or stays were replaced, the boat was allowed to sit for a day or more to allow some prestretching and the tensions and alignments were rechecked and adjusted accordingly. Then the boat was sailed. Some owners took a rigger along, but most sailed their boat and made their own observations. The critical observation was that when sails were full, and the spar and rigging fully loaded, that the mast was essentially straight and/or that there was there a smooth, fair curvature.

It was assumed that the mast would not stay perfectly straight when loaded, and so shroud tensions were set to achieve a desired curve. There was a fad of cocking the masthead to windward when the lower shrouds were stretched under load, which was supposed to help going upwind. Today, we tend to adjust rigs for some sag at the masthead to leeward in a breeze in order to depower the rig.

In those days, no shroud was ever supposed to go slack, but today the tendancy is to set up rigs with flexible spars so the lee shrouds feel slightly soft when hard on the wind in stronger winds. On most but not all classes they should not be flopping around.

If any rigging was replaced, Owners were advised to check their rigs several times during the first season as the shrouds and stays would continue to stretch most dramatically when first being used and less so over time. At some point they settle in and should not need frequent adjustment.

Now all of that said, on race boats, we typically have different shroud tensions for different wind strengths and will adjust the shrouds for almost every race. And of course, we change backstay tension with almost every long gust.

Respectfully,
Jeff
 
  • Like
Reactions: casey1999
#55 ·
Jeff,

Yes it could be possible that it takes 2-4 days of 6-8 hr days to stretch the rigging if you will on a V70, hence the quote I am remembering. But being as there was not explanation.....one does have to swag on the reasons why. Stretching of the rig is probably #1, along with getting things adjusted length wise to the 1/16" vs as one fellow I know that races on these, ie a sailmaker, for a cruiser, 1/8-1/4" difference per shroud etc per side is ample.

My boat when I bought her from the initial owner, the mast was almost an inch or two out of center, wires were in the 3-5% of breaking strength. Probably works well for the light wind days overall here in puget sound, but still, i find about 15% is a better overall tightness for my boat, then adjust the back stay while sailing. Even then not sure I have things absolute perfect all the time. I'm trying to get things with in 1/8" per side. Took some rake out, got better helm feeling etc.

Not sure frankly, that setting a rig up, then leaving alone per say is the way to do things. Constant checking is the way to go. This will also allow one to hopefully look at and find issues that may cause total failure. Then again....one never knows.

Marty
 
#57 · (Edited)
Doug
I just got off the phone with my son. Stephen is a rigger at one of the busiest shops in Annapolis and has been doing this for quite a few years.
i asked about your situation and got some more information for you.
1. He mentioned the same thing one of our SailNet posters did about the designs. Some chainplate designs have curves and bends so during heavy use they flex and after thousands of cycles can become damaged and fail faster than more robust designs. If you have a boat like that you have to consider your chainplates to be even more disposable than usual.
2. The older a boat is the more likely it has been hit by lighting. This can damage the metal of chain plates.
3. Many boats include the chainplates in the grounding system. This can be a good thing but if something goes wrong you can loose some metal.
4. A temporary failure of a shroud can cause extream loading on the remaining shroud and chainplate causing it to fail prematurely. Sort of like the 30% rule on the wire.
5. Shock loading by poor tuning of the rig can cause extreme load of one chainplate causing pre-mature failure.

So at the end of the day the whole boat is a system. Neglect or failure of any component can cause wear and failure on any related component.

Another item I just remembered that we discussed last summer. I don't know if this could possibly apply to your Gulfstar but some lighter boats are currently a lot more flexible than they were designed to be. A boat that that has been ridden hard may have some damage to the hull laminates that will cause the boat "banana" more than specified when the full back-stay tension is put on it. In heavy weather conditions the weak boat would transmit some of the extra loading forces to the chainplates.
So this just goes to show it is a system where the design, quality, maintenance and loading of every component can easily combine to cause the failure of one part.

In your case it appears as if all of your experts are partially right.
The lessen is however that chainplates should be considered a consumable item just like:
running rigging, zincs, standing rigging, sails, impeller etc.
They may not be consumed as fast as the zinc but they may not last the life of the boat either.

This is especially true in off-shore sailing where the rig can be subject to repetitive shock loads for days at a time. In fact a rig inspection is probably prudent after every storm.
You can and should do it yourself.


That being the case the design and accessibility of the chainplates is probably as important as the location of the oil dip stick and stuffing box. This may affect the choice of boat.
 
#63 ·
Doug
I just got off the phone with my son.
As far as replacing standing rigging how far should one go? Should I replace all bolts that hold tangs and the spreaders? Should the spreader fittings be removed to inspect for mast corrosion (my fittings wraps 3/4 of the mast circumference)? Should all fittings that are rivited be removed and new rivets installed?
 
#70 ·
The thing I find interesting about failure of sail boat rigs is that there seems to be this big unkown about if the rig is good or not. Because of this unkown, we are told best to replace say every 10 years.

Now where I work I have just be assigned to be weight handling (lifting) inspector. I have started some training on inspecting weight lifting equipment- cranes, hoist, shackels, lifting cables, slings. This is for lifting things that failure is not an option. It just seems like a simple inspection is good enough for these items, and if they pass they rarely fail. But with sailboats, seems even with good inspection, they still, and regulary do fail.
 
#71 · (Edited)
Are you sure about that. I was under the impression that if you had a crane cable that was in service for 30 years someone would think about replacing it.:)

Don't you keep records of replacement and inspections for all were parts? How old are the oldest parts?
Also is shock loading much of an issue?
What is the safety factor engineered in?
Are your parts stainless? The old time riggers say that super heavy iron rigging brushed with tar and oil every day lasts for almost ever and is easy to see if it is rusted and needs to be replaced.
Stainless is much cleaner for sails and decks and can be ignored for months but hides its impending failure better than plain steel that is continually greased.

Your the expert but I suspect that in an industrial setting a 5 year part and certainly a 10 year part just wouldn't even be around. On a sailboat we figure hey it's stainless, looks good and is only 30 years old, lets go sailing.
 
#76 ·
"Sail & Rig Tuning" by Ivan Dedekam"
I have this book and was re-reading last night- very good book. One thing Dedekam says is to tension the rig as tight as possible, with forestay (as I remember- going above 30% uts). According to other posters, this could lead to fatigue failure over time.- Thoughts?
 
#91 ·
Do you mean using your formula? I'm looking at the book, and don't see "tight as possible" though I certainly could be missing something. For masthead rigs, he says adjust forestay/backstay to a achive rake, then adjust forestay sag (forestay tension, correct?) by adjusting Backstay. He states that boat designers often choose 30% to 40% of the stays breaking load as Max allowable Backstay tension. He says adjust to 30% and mark as Max., then back off the adjustment to 2/3 of Max. I guess using your formula that does bring the forestay over 30% on your boat. Wonder what "boat designers" would say?
Regarding cap shroud tension he suggests pre tensioning cap shrouds to 150kg, (In one example). "Pre tension acts as a shock absorber in variable wind strengths and the masthead is kept under better control."
 
#81 ·
Dynamic Tuning is explained in Dennis Conner's book, Sail Like a Champion.
First you tune the rig to specs, generally 12-15lbs on upper shrouds, 15lbs on lower shrouds, and 10lbs on foestay. Backstay is used to bend mast to point better, or slack-off downwind.
Take the boat on a 10-15kt day, go from a close reach to a beat. Observe the leeward shrouds for slackness and tighten them just until the slack is gone. Remember how many turns you had to make on each shroud. Change tacks and do the same thing on the leeward side. He then recommends doing the same thing in 15-20kt winds.
When you get back to the dock measure the distance from the top of the mast to each shroud, using your main halyard. Make sure they are all equal. If they are not then you must make them equal by re-checking the tune and making adjustments accordingly.
Take her back out and repeat the process. It is a lot easier and faster if you make your distances equal with proper tune before you go out the first time.
Depending on your rig, you may have to sacrifice tune to get an equal distance, but not by much! Warning: don't overtighten rig to get equal distances. If it comes to that then the mast is not stepped on the c-line of the boat or your shrouds are of different lengths.
 
#98 ·
This is excellent / valuable information! I can't wait to close on our CT 56 in July and utilize all the great information here!

I sure do want to learn how to properly tune my rig. My previous / haphazard methods, were proven to have a down side....

I used to just pull on the shrouds / stays, at the dock, and adjust them to "feel" equally tight. That was all, and surprise, surprise, considering the ramifications, that was not enough.

Thank you very much gentlemen!
 
#101 ·
This is excellent / valuable information! I can't wait to close on our CT 56 in July and utilize all the great information here!

I sure do want to learn how to properly tune my rig. My previous / haphazard methods, were proven to have a down side....

I used to just pull on the shrouds / stays, at the dock, and adjust them to "feel" equally tight. That was all, and surprise, surprise, considering the ramifications, that was not enough.

Thank you very much gentlemen!
Good luck on your new boat. I'm sure the days are dragging while you wait.
Just to reiterate. It seems unlikely that rig tuning even if not perfect would be the major cause of chain plates failing.
The real lesson is that any stainless chain plate that is over 10 years old and certainly over 20 years old could likely be work hardened and even if it looks perfect and polishes beautifully should be considered for replacement.
 
#106 ·
It worked!

Tuned under sail using the method I mentioned in #97. When I returned, I mesured the tensions in Cap shrouds. Both match (980 lbs) and are just below the initial tensions recommended by Loose for 9/32 rigging (1050). While tuning, I thought that I could have eliminated some more slack with another turn on the turnbuckles, but wanted to verify the tensions first. So...the system seems to work nicely.
Here is a link to the same method for J 22's, suggesting they "lose the gauge". In any case, it's nice to know both methods seem to produce similar results.
Thoughts on Tuning - Lose that Tension Gauge!
 
#107 ·
Re: It worked!

Tuned under sail using the method I mentioned in #97. When I returned, I mesured the tensions in Cap shrouds. Both match (980 lbs) and are just below the initial tensions recommended by Loose for 9/32 rigging (1050). While tuning, I thought that I could have eliminated some more slack with another turn on the turnbuckles, but wanted to verify the tensions first. So...the system seems to work nicely.
Here is a link to the same method for J 22's, suggesting they "lose the gauge". In any case, it's nice to know both methods seem to produce similar results.
Thoughts on Tuning - Lose that Tension Gauge!
When I go to the link some of the number (number of turns and tensioin) show up as a square. Do you know why?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top