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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #11  
Old 01-22-2012
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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.
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  #12  
Old 01-22-2012
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Quote:
Originally Posted by davidpm View Post
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.

Last edited by L124C; 01-22-2012 at 04:26 PM.
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  #13  
Old 01-22-2012
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Quote:
Originally Posted by L124C View Post
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.
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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.

Last edited by davidpm; 01-22-2012 at 05:12 PM.
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Old 01-22-2012
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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.
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Old 01-22-2012
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Quote:
Originally Posted by davidpm View Post
DougSeabag mentioned that a major lesson he learned from his last boat was the importance of dynamic tuning of the rig.
Welcome back Doug
[I]"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.
[I]
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.

Quote:
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.
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Old 01-22-2012
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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.
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Last edited by Landgull; 01-22-2012 at 07:00 PM.
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Old 01-22-2012
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Quote:
Originally Posted by davidpm View Post
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.
Since Doug wrote that a chainplate failed, I would guess that he is attributing at least some of the cause to shock loading from loose shrouds.

When we replace a rig, we do what we call a static or dock tuning. Meaning that we make sure the mast is in column, has the original amount of rake, (unless the customer wants it changed), and that the top of the mast is as close to the middle of the boat as possible.
Then we tension the rigging according to a what we feel is appropriate and instruct the customer to take her sailing and check the tuning in various wind conditions and points of sail.

There is a certain amount of initial stretch with new wire and all new rigs should be re-tensioned after the boat is sailed a few times and then checked once in a while while under sail.

Tuning is something that everyone should be able to do on their own boat if they plan on crossing oceans.
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Old 01-22-2012
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How does one confuse, this new word to me, "dynamic tuning" with chain plate failure?
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Old 01-22-2012
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Quote:
Originally Posted by Landgull View Post
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.
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  #20  
Old 01-23-2012
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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.
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