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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?
 
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#2 ·
I do the rig on my Catalina 309. Start by tensioning everything to 15% of breaking strength, followed by tweeking it under sail. Not super nit-picky about it, but like the idea of it being done right.

How important is it? From a safety standpoint, it's good to know that the rig is going to be at its max for strength. From a performance standpoint, it sure makes her point, as compared to the slack job that the dealer did.
 
#3 ·
I have raced OD keelboats for a very long time and never heard of dynamic tuning - some of the Boats I raced were exceedingly finicky about rig tuning, but we always just called it tuning the rig.

Can anyone define dynamic tuning ?
 
#4 ·
I'm guessing that this is referring to the tuning adjustments made under sail after initially putting the mast in column and setting prebend.. but I've not heard that specific term before either. A google search does not turn up any direct references to such a term.

All we've done is set up the mast reasonably at the dock, then go sailing and observe any sag or lift in the column of the spar when hard on the wind.. observe both tacks, make some judgements on whether the top is sagging off excessively or if the mast is being 'held high' or allowed to sag at the spreaders and then adjust the respective shrouds accordingly. We always made the adjustments on the unloaded (lee) side and then tacked back to recheck.
 
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#6 ·
I'm waiting for Doug to weigh in as he mentioned that the tuning of of his last boat, or lack their off caused a lot of trouble.
 
#7 · (Edited)
I highly recommend a little book "Sail & Rig Tuning" by Ivan Dedekam. Think it will cover all you questions. He shows how to tune your rig and fine tune it under sail which he cleverly calls "Tuning under sail". In addition, Dedekam writes simply and concisely. I've picked up the book "Riggers Apprentice" a couple of times and put it down promptly when my head started hurting! Tunning is certainly important, but is not Rocket Science IMHO!
BTW, this thread probably should be posted in Gear and Maintenance, not Seamanship.
 
#13 · (Edited)
I highly recommend a little book "Sail & Rig Tuning" by Ivan Dedekam.
Since I have every book on sailing I'll just go look that one up.:)
Thanks

It is illustrated with pictures on every page.

I'm still waiting to hear from Doug as to why he figures rig tuning caused him to loose his boat assuming I understood his post correctly.
 
#8 ·
The same is done seasonaly when we step our mast, first it is snug into place followed by a tune up sail, A quick look up the mast to look for any undesireable bends, the stays are then tweeked on the leeward side and locked into place for the season. Ive tried to use the stay tention tool but the results I got did not seem right. so now its done by eye,feel and experiance.
 
#9 ·
I have tuned many boats the exact same way Faster has by tacking back and forth, but once the shrouds are tensioned thats it.
I think the term dynamic tuning is referring to a backstay tensioner or a jackstay, as you can make substantial adjustments easily while on the fly.
If not then I have no idea.
 
#10 ·
Just by the denotation of the term, dynamic, I would expect that dynamic tuning would be adjusting the rig differently as conditions change; however, the earlier posts suggests that this is just referring to tuning under sail and not sitting at the dock.
 
#11 ·
I think David is using the word "dynamic" in it's ordinary usage, and not as a term of art. The definition of "dynamics" is "a branch of mechanics that deals with forces and their relation primarily to the motion but sometimes also to the equilibrium of bodies." Adjusting something dynamically means that you are adjusting it while it's in motion, as opposed to when it is static. When you balance an automobile tire statically, you find where it's center of gravity should be, and then add weights to it until it appears to be balanced. When you balance a tire dynamically, you spin it, and add weights until it spins smoothly, without vibrating.

Using that definition, dynamic tuning just means tuning the rig while it is in motion and under load. Tuning the rig at the dock is, to a certain extent, educated guesswork. From experience, the person tuning the rig knows the mast should generally be erect and symmetrical, with a certain amount of tension on the stays and a certain amount of rake and other characteristics, but you don't know for sure how it will behave until you sail it, with the rig in motion and under load. I always tune my rig in the slip first, and then sail it and make sure that it behaves the way it should when the boat is in motion and the rig is under load.

I think most sailors make too much of rig tuning. For the average sailor (casual cruiser and occasional beer can racer), it's enough if the rig is straight and erect, with enough tension on all the stays to prevent the rig from moving around in a seaway, and with enough rake to produce a comfortable amount of weather helm. You can find lots of books and other sources with clear instructions on how to achieve those basic objectives, and most people don't need to pay someone $100. an hour to do it, if they just don't allow themselves to be intimidated by the thought of it. Fine tuning the rig for optimal performance in light air or big winds requires a little more knowledge, but it's the kind of thing most people can learn with experience and a little reading.

If your first thought is to read about how to do it and then try it yourself, the likelihood is that you'll achieve a satisfactory result, and never again be intimidated by the thought of it. If, however, your first thought is to hire someone to do it for you, you'll never get beyond the mystery of it.

If you have a trailerable boat, and have to rely on a pro to tune your rig, you'll be reluctant to trailer it anywhere, because you'll have to hire someone to rig it for you when you get there, and then hire someone to re-rig it when you get it home. It's well worth the effort to learn how to do it yourself.
 
#12 · (Edited)
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.
Dedekam stresses that tuning under sail must take place in winds that will heel the boat 20 to 25 degrees before the seas build up. Tough to coordinate that with a Rigger! In addition to saving money, it's good to DIY so that you understand the principals involved. He also covers Sail tunning which is probably the "dynamic" aspect you are referring to. Being a Windsurfer (where efficiency can mean the difference between sailing and swimming home!), I was shocked at how clueless some Skippers are to proper sail shape in general, much less in changing conditions! For example: there are several options before reefing a Main. I think most racers know this (they certainly should!), but many recreational sailors don't. I sailed with one skipper who's Main was screaming "Tune me, Tune me!", but all he did was look at his GPS and adjust his point of sail to get the (relatively) fastest speed! Not only is this not efficient, it's hard on the boat and crew. Anyway...I digress. The book covers all in short order.
 
#14 ·
First, you replace your turnbuckles with electrohydraulic actuators and strain gauges. Then you have your sails bar coded, which is not as bad as it seems since the bar arrays are only located in a couple of dozen discrete positions. Now we add eight cameras (typically) to monitor the sail shape (like a facial recognition system) and a small computer system to control the actuators. The entire rig is then dynamically tuned under load, to keep all the rigging within design parameters for tension but also to optimize the sail shape.
Of course the professional version requires installing computer controlled winches as well, and tension guages on all halyards and sheets, so that the sails can also be properly tensioned. It's really all old technology, just never made mass market because, well, even at today's cheap hardware prices most recreational sailors can't afford it.

Back on the other planet...
Yeah, even 30 years ago you'd find J/24 sailors retuning their rigs before every race to match the expected wind conditions. Mast rake, tension, they'd have a little card and change everything just a little bit to match the expected wind range. But on cruising boats with "ain't-gonna-bendy-me" masts? Nuh-uh. Kinda sounds like the riggers have found a way to finesse the ultimate in rig tuning--and book a *hitload more billable hours in the process. The kind of stuff that a local rock start from the local sailing loft used to do for free when you bought new sails.
 
#61 · (Edited)
Hugh?

First, you replace ..... INSERT CONDESCENDING SARCASM......market because, well, even at today's cheap hardware prices most recreational sailors can't afford it.

Back on the other planet...
Yeah, even 30 years ago you'd find J/24 sailors retuning their rigs before every race to match the expected wind conditions. Mast rake, tension, they'd have a little card and change everything just a little bit to match the expected wind range. But on cruising boats with "ain't-gonna-bendy-me" masts? Nuh-uh. Kinda sounds like the riggers have found a way to finesse the ultimate in rig tuning--and book a *hitload more billable hours in the process. The kind of stuff that a local rock start from the local sailing loft used to do for free when you bought new sails.
I assume you are referring to the book I recommended. I purchased it because my boat had excessive Weather Helm on Port Tack. It not only allowed me to cure that problem, it taught me MANY other things in the process.
As I recall, it set me back all of $15 Dollars. Yeah....I'm sure the author is sitting in a big house on a hill, counting his wealth!
I honestly suspect he has forgotten more about sailing than I will ever know, and I thank him for sharing some of that knowledge!
BTW I can certainly effect the efficiency of my Main using the back stay. Do I use it for Bay Sailing? No. Would I use it if I was racing seriously with a crew or cruising on the same tack for extended periods when it would be beneficial and worth the effort? Yes.
 
#15 ·
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.


The way I understand it, nothing HAS to be done if you don't want to do it. As for "dynamically"(under load and conditions) tuning one's rigging depends on varying factors. Type, size, condition, use and age of ones standing rigging. But the stepping of the mast doesn't require dynamic tuning.

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.
This is quite true on all levels. If you have the money go for it, but self tuning can be done with a little knowledge, the right tool(s) and help from somebody who knows what they're doing.
I'm not sure what everybody else does, but we check the rigging (with a gauge) once a month or if there's a big temperature change, especially the backstay antenna. As our boat has an adjustable mizzen/main backstays through the triadic so I'm always keeping an eye on the shrouds and their adjustment(s) and tune them periodically depending on our sailing conditions. One thing's for sure, if you find them rattling away in their chain plates while at dock, you might want to attend to your rigging.
 
#16 · (Edited)
Doug and I discussed this the other night in the chat. He was claiming that his chainplates had failed because a lack of "dynamic tuning" had caused excessive forces which exceeded the strength of the chainplates. However, by the very design and nature of chainplates, if they are intact, they essentially can not fail. Firstly, a chainplate needs to be built AT LEAST strong enough to handle the maximum righting moment of the boat. That is to say, there is no force that the wind could exert on a sail that could cause the chainplate to fail. Secondly, the chainplate should be made more strong than the shroud. While these are both "zero-tolerance failure" components, in an excessive event, you want the shroud to give before the chainplate, as that will reduce any likelihood of damage to the hull. Add in large safety factors, and it is impossible for the wind to cause a chainplate failure.

"But, that's ridiculous!" you shout while throwing empty beer bottles at me. "Chainplates fail all the time!" Well, yes, they do, and it's because they're a limited-lifespan part. You see, stainless steel has a big, and rather undetectable problem from crevice corrosion. Dave's chainplates in question were from 1975, and as I explained above, if they hadn't been corroded, they couldn't have failed. The problem is, chainplates aren't considered the same way as shrouds are as having a limited lifespan before replacement. This is problematic since crevice corrosion doesn't necessarily show outward signs of weakening before it fails. What would be a good decision, if one is set on the use of stainless as a chainplate material, is to replace it at the same time as the rest of the standing rigging. Two alternatives would be to use bronze or titanium (or some of the more advanced integral chainplate options, but I don't understand the engineering considerations behind them well enough to explain.)

The bottom line: Dynamic rig tuning might give you an extra couple of knots per day, or an extra bit of weatherliness, but it would not have prevented the failure of S/V Triumph's chainplates. Chainplates made from stainless are a limited lifespan part, and there have been a number of failures to prove this out, either replace them on a schedule, or change them out to a material with a longer service life. It's doubtful that this extra cost of replacement would even be as great as the extra cost of a dynamic tuning job, but it would provide much more security in knowing you have a "bulletproof" part.
 
#19 ·
Doug and I discussed this the other night in the chat. He was claiming that his chainplates had failed because a lack of "dynamic tuning" had caused excessive forces which exceeded the strength of the chainplates. However, by the very design and nature of chainplates, if they are intact, they essentially can not fail. Firstly, a chainplate needs to be built AT LEAST strong enough to handle the maximum righting moment of the boat. That is to say, there is no force that the wind could exert on a sail that could cause the chainplate to fail. Secondly, the chainplate should be made more strong than the shroud. While these are both "zero-tolerance failure" components, in an excessive event, you want the shroud to give before the chainplate, as that will reduce any likelihood of damage to the hull. Add in large safety factors, and it is impossible for the wind to cause a chainplate failure.
I agree, you could tune your rigging to play Stairway to Heaven in a 30 knot blow, but if your chain plate(s) fail it's because you're singing a different tune. Failure of the the chain plate has nothing to do with with how in tune your have your rigging.
 
#20 ·
If you don't know the numbers, then get the mast in column. If the leeward shrouds go slack in less then 15 true, tighten them 1/2 turn at a time. That'll get you close, and keep the stick up.

If you want more info, look into a tuning guide from a sailmaker or go out and do some testing yourself. Less tension for lighter air, and more for heavy air, keep a log of tuning settings, conditions, and results. It honestly doesn't take more than a few trips out.

Buy a good gage. It makes a big difference on almost all boats. Cruisers probably won't notice any difference.

As far as dynamic, in most racing you can't change the rig tune while racing. That would truly be dynamic. You can change rig tune on most OD boats between races, and it frequently gets done. Especially in the J24s and Bene 367s.
 
#21 ·
In some OD classes, you can't even change certain parameters of the rig between races.

Dynamic Tuning ? - so that is like when we are late to the start, rushing to get out there in sloppy chop, and I have my mainsheet trimmer drive while 3 of us try not to lose any tools overboard while fiddling around with with the leeward shrouds

is it getting looser or tighter ?
Where the ring ding go ?
NO you cant tack - wait !
 
#22 ·
What about backstay adjusters? When you round the weather mark and ease a backstay adjuster, or, when you start to become overpowered on a windward leg and you increase the tension on the backstay adjuster, bending the mast on a fractional rig, or reducing headstay sag on a masthead rigged boat, doesn't that make a radical change in rig tuning on the fly? It seems to me that using a backstay adjuster is the essence of dynamic rig-tuning.
 
#36 ·
You're right "using a backstay adjuster is the essence of dynamic rig-tuning", but Pythagoras' rule comes into play; tighten the backstay, the forestay lengthens (or rather the distance between the top of the mast and the furler gets longer). Furthermore, that's why the shrouds should be toggled (and that they're functional, not seized). You're better off being a bit sloppy than overtightened.
 
#23 ·
Hello! Sorry that I took awhile to comment on this thread! I made that big claim and then left it to you guys to fill in the details; not on purpose, but that's how it happened.

Anyway, since the concurrent breaks of 2 starboard main chainplates, while crossing the Atlantic last summer, I've had numerous opportunities to discuss this with people.

What seems to make the most sense, besides the suspect underlying condition of the chainplates themselves, is that without having tuned the rig while under way after the stepping of that mast, the mast in question was most likely vibrating / wrenching forward and backward in relation to the boat.

This "fits" with what I saw of the broken chainplates; i.e., they broke at the point where the chainplates were sticking up from the ribs of the hull where they were thru bolted to.
These "tabs" were perpendicular to the boat. Lets say they were 4 inches wide; well the plane of those 4 inches was perpendicular to the plane of the hull. Such that the portion of the chainplates sticking up, above the ribs, sticking up and through the deck was like a tab of metal.

Those tabs broke, just below the deck. And it appeared as though they broke from being bent, forward and backward, repeatedly, until the bending caused the infamous metal fatigue which will break any metal.

Now, many people will claim that using titanium or perhaps bronze chainplates, and ideally bran new ones, wouldn't have sufferred this breakage. But, shy of actually testing new ones vs. old ones, with and without the tuning which should keep that mast vibration / wrenching from occurring, I can not agree that it is OK to not fully tune your rig if you have new / titanium / bronze chainplates.

Without properly tuning the rig, you are abusing the chainplates / metal, with an eventually disasterous result, regardless of the intitial strength of the metal.
What will be effected by the quality / age of the chainplates, is how long they will last given this abuse. But, it is abuse, nevertheless.

For me, I would choose to sail across the Atlantic with old chainplates, as long as the rig was properly tuned, as opposed to with new chainplates without properly tuning the rig.

Now, what is this "dynamic tuning"? Well, as was described to me, by more than one source, is basically what a few of you did describe here already.

After installing your mast, and adjusting all the turnbuckles to provide a similar / tight tension of the stays / cables at the dock, per your specific boats' rigs' pounds of tension requirements, you are then supposed to take her out under full sail, and adjust the downwind turnbuckles again.

Yes, this would include all the shrouds / stays, i.e., the backstays, etc., all of them.

Now, as for the exact amount of tension to set these to, I am pretty sure this varies by boat and rig.

Many of you apparently already know this, so this isn't anything new to you! For you, fair winds, and have a great day!

But, for the poor saps like me, especially those who are stepping their mast(s), I highly suggest asking your rigger about the final / dynamic / "tuning under sail", and, or, read that book suggested earlier! Because, as was quoted, 2 riggers who were hired by us for our main mast stepping process in Fort Lauderdale never mentioned a thing about this, and it didn't take all that long for the repurcussions of not doing this to become my worst night mare.

Without having read that book, I would greatly appreciate, as many others might, any specific inflormation about how to dynamically tune your rig, per these experts, or any other information about these specifics.

Because all I have heard is to "tune the downwind stays / shrouds" while underway".
And that still leaves much to the imagination about the details.... :)
 
#24 ·
Sailormon, yes it is. Some classes even let you adjust mask rake on the fly, but it all depends on the class rules. OD, handicaped, IRC, ORC, MORC, IOR, etc.

Usually the class will limit the puchase of the backstay, or state that it must be 'fixed' and not adjusted during the race.
 
#27 ·
I keep hearing things like: If you have titanium chainplates, or, things like the prior comment: If the standing rigging is toggled correctly.... then what? You don't need to tune your rig correctly?

I really think it's more like having oil in an engine.... without it, it is just a matter of time, no matter what kind of engine, or how things are adjusted; you don't want to abuse metal if you want to get the full "life" from those parts.

As far as how much a mast has to "pump" to cause metal fatigue to ruin / break a chainplate, well, from what I understand, you really don't want any pumping at all.

Sure, there will be some flexing from wind changes, but when it gets to the point of having a vibration / pumping action, something is really wrong.
 
#28 · (Edited)
I dynamically tune my boats ... but I have a healthy dose of material science, metallurgy, engineering, amateur sailmaking, etc. background; so my reasons may be quite different from anyone else.

I dynamically tune for the following reasons:
1. first and foremost - sail shape ... if the forestay tension (improper sag when windloaded) doesnt precisely match the leading edge shape of the sail as cut/designed, then I readjust (while underway) to get it 'close'.
2. Most rigging is stainless steel and that presents a special problem all by the very nature of 300 series stainless --- vulnerability to fatigue failure. Fatigue is vastly accelerated any time 300 series stainless is cyclically loaded beyond ~30,000 psi (even that the material has a ~90000 psi 'ultimate tensile strength' ... but that applies only to 'ductile failure' & non repetitive load conditions). The all important material characteristic for 'boat rigging' and plates, etc, I adhere to, is that I expect that the material/rigging WILL catastrophically fail when there are more than (estimated) 1 million 'cycles' (about 1 circumnavigation) where the component goes beyond 30K psi. Keep that loading UNDER 30K psi (30% of rig tension, etc.) and the part 'can' last virtually 'forever' (theoretically from a materials science or metallurgical point of view).

So, I do use a tension gage the rigging while getting the boat over 'towards' a 45° heel angle ... as after the 45° heel angle the loads diminish due to 'trigonometry'. If I cant get the boat to 45° I simply measure what I have at the max. angle and then calculate what the loads would be @ 45° over, etc. ... and then assuming that my rig has an appropriate inbuilt design safety factor (probably at least 3X+ for a "perry-boat") I arrive at the max. tension and then reduce the 'static' tensions as needed and still to get the needed mast 'pre-bends', forestay 'shape', etc.
When Im sailing 'hard', I simply dont want any part of the rig tension to (much) 'go over' 30% UTS ... and will apply 'helpers' (runners, etc.) to get what I want ... (hopefully) less than 30% UTS at 'max'. conditions.
When 'sailing' I monitor the backstay tension (gage attached) and if that backstay is going much over 30%, I then reduce/reef of change a sail, head off, etc. etc.
(FWIW I sail a Taiwanese made Ty37 and the Formosans are long noted for their lack of metallurgy expertise ... and I claim so too many 'riggers' also fit in this category but 'graciously understand' and 'accept' this .... as I dont want my cost of maintenance exceeding the cost of the national debt of the USA.).

I didnt do this when I was actively racing my 'sport boat' (dynamic on-the-fly mast raking and 'very' bendable mast, independent forestay tension, etc. and over-design Safety Factor of 1.5X) and did lose a few masts, rigs, etc. overboard - all due to 'catastrophic' fatigue failure.

Thats my 'impression' of dynamic tuning ... for sail 'shaping' and for keeping the rig up without undue fatigue failure 'surprises'.

Ultimately one has to consider that since there ARE noted rig failures, increasingly insurance underwriters demanding (panic, seemingly) a total rigging changeout every 10 years, etc. ... that the 'inherent design and selection' of the these materials ... is quite 'faulty' ... and 'someone' is erroneously designing rigging etc. in accordance to 'ductile' values and not 'fatigue endurance' values. Cant be otherwise.
 
#30 ·
2. Keep that loading UNDER 30K psi (30% of rig tension, etc.) and the part 'can' last virtually 'forever' (theoretically from a materials science or metallurgical point of view).
.
So if I keep loads under 30K psi and inspect for corrosion and cracking (and find none)- can I keep using the standing rigging, or should it still be replaced say every 10 years?
 
#29 · (Edited)
I am also concerned with my rig and truly only feel confident in it after I do the inspection and tune it myself. I purchased a Loos rig tension gage (model PT3-M) so I could determine the tenstion of all shrouds and stays. The tension gage can be used while under sail, so it will give me real time rig tensions.

The instructions that came with the gage say you should tension the rig at the dock (several tension values are given depending on your rig). 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 (dynamic tune?). As long as there is no slop in your rig including mast pumping, and the tensions are close to what is considered typical, rig should be considered well tuned (assuming rake and mast bend are acceptable).
 
#35 ·
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. :)
 
#31 ·
Most insurance carriers now (in the fine print of most of their policies and 'renewals') require rig changeout every ~ten years ... even if the rigging is stored in a box and not used, etc. Or if damage occurs because of rig failure and the rigging wasnt replaced in that time frame ... casualty loss not covered!

You better have previous receipts to prove this if you do have a failure or casualty loss, etc. One really has to actually read the fine print of your policy.
 
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