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Standing Rigging Tuning

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Derek Crawford
Master Marine Consultant

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USA
3321 Posts

Response Posted - 08/04/2003 : 22:43:52

Steve - thank you very much for your kind thoughts on my Sis-in-Law she is still critical and not showing improvement so we can but hope...
Derek

<img src="http://im1.shutterfly.com/procserv/47b3dc30b3127cce942c608d6f1e0000001010" border=0>
TRFK#2262"This Side Up"

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Shawn
1st Mate

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USA
62 Posts

Response Posted - 08/07/2003 : 22:23:24

Steve,
Thanks for the explanation on rig tuning. I have been setting mine up with the fore and back stays equally tensioned (as close as I can get them by feel) then the upper shrouds with slightly less tension, followed by the forward lowers looser than the uppers, but tighter than the aft lowers. Your explanation makes a lot of sense, and I will give it a try. One question. As I said, my order of tension goes, back stay and fore stay taut, upper shrouds, forward lowers, aft lowers. With your set up, where would the upper shrouds fall in order of tension? Also, I do have a backstay adjuster. With it slack, How much deflection do you give the fore stay (ballpark guess)?
Thanks for the advice.

Shawn
1980 C25 tr/fk #1960

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Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 08/08/2003 : 09:20:54

Shawn,

When this subject came up awhile ago, I wrote the following:

Tuning the Rig of a C-25

Before we discuss the processes that should be used in tuning your rig, let’s think about how each stay functions. Each stay has a specific purpose, to provide support from a specific direction, and to prevent the mast from bending in an improper direction or to an excessive extent. If your rig is properly tuned, the tightened backstay will pull the top of the mast aft. The headstay will limit the distance that the top of the mast can tilt or bend aft. The forward lowers will resist the pull of the backstay and prevent the lower part of the mast from moving aft. At the same time, the forward lowers will provide lateral support to the lower portion of the mast, to keep the lower part of the mast from sagging to leeward. The uppers will provide lateral support to the top of the mast, to keep it from sagging off to leeward. As the tension on the backstay adjuster increases, it will exert a downward force on the mast. The mast step and keel will resist the downward force on the mast. Since the mast can't move downward, to release the pressure, the mast will bow in the middle. Because the forward lowers are adjusted snugly, and the aft lowers are adjusted loosely, the lower part of the mast can only bend one way, i.e. forward. As the lower part of the mast bows forward, the aft lowers will become taut, and prevent the mast from bending so far out of column as to damage the mast. In order for the backstay adjuster to work properly, the stays have to be adjusted with differing tensions, so that they allow the mast to bend in the proper direction. If all the upper and lower mast stays are snugged down to more or less the same tension in all directions, when you pull on the backstay adjuster, the mast won’t bend, because the stays will prevent any part of the mast from moving in any direction.

Boat Without Adjustable Backstay

Begin tuning your rig by alternately tightening the headstay and backstay turnbuckles until the headstay and backstay have little or no sag, but so that they are not bar-tight.

Next, loosen all your lower stays just enough to take the tension off them. Then, tighten the upper stays snugly by an equal number of turns on each side. Next, take your jib halyard, and use it as a measuring device (you might need to tie a piece of line onto it, to lengthen it), to make sure that the distance from the top of your mast to the chainplate for the upper stay on the starboard side of your boat is the same as the distance from the top of your mast to the chainplate for the upper stay on the port side of your boat. If the distance is not equal, adjust your upper stays until the distance is equal on both sides. That will ensure that your mast does not lean more to one side than the other.

Now, adjust your forward lower stays until the slack is just taken out of them. Then continue tightening them, alternately by an equal number of turns, until they are as tight as you can comfortably get them by hand. Then do the same with your aft lowers. Lie down on the coach roof, and sight up the mainsail track, to see if the mast is straight. If so, then use tools to tighten each lower stay a little more, alternately by an equal number of turns, until the tension of the lower stays is snug, and equal all around. Sight up the mast again to be sure it is still straight. If it is not, then make such adjustments to the lower stays as are necessary to make it so.

Tighten the locknuts on all your turnbuckles, including the uppers, lowers, headstay and backstay. With these adjustments, your mast will not be perfectly adjusted, but it should be "in the neighborhood." Sail the boat, and observe whether it has excessive weather helm or lee helm. It will probably have excessive weather helm. If the boat has excessive weather helm, readjust all the stays so that the entire mast is tilted further forward. If the boat has excessive lee helm, readjust all the stays so that the entire mast is tilted further aft. If you do not have an adjustable backstay, you are done.

Boat with Adjustable Backstay

If you have an adjustable backstay, you have a little more adjustment to do. Make sure that the tension on the backstay adjuster is completely released. Then loosen the turnbuckle on the headstay until the headstay is slack. Next, adjust the aft lowers until they are slack. Then apply strong tension to the backstay adjuster. Adjust the headstay so that the mast tip bends aft about 8-9 inches when the backstay adjuster is tensioned. When the backstay adjuster is eased, the headstay should be quite slack. Adjust the aft lowers so that they become tight when the backstay is tensioned. The way to do that is to apply the maximum tension on the backstay adjuster. Then adjust the aft lowers until they just become taut. When you release the tension on the backstay adjuster, the aft lowers will become slack. When you re-apply the backstay tension, the aft lowers will become taut again. To increase the amount of mast bend, loosen the headstay and the aft lowers, but do not allow your eagerness for speed to cloud your judgment.

Sail the boat again, and observe whether it has excessive weather helm when the backstay adjuster is fully tensioned. If the boat has excessive weather helm, then readjust all the stays so that the entire mast is tilted further forward.

Using a Loos Gauge to Tune the Rig

I don’t own a Loos gauge, and have never used one to tune my rig. I make sure that the mast is vertical, adjust the stays so that they are generally snug, and adjust the rig to allow the mast to bend within safe parameters, and no more. Then I test-sail the boat after tuning the rig, to see if it is performing to my expectations.

Having said that, I believe that most sailors would benefit from using a Loos gauge. Once you have tuned your rig so that the boat is very fast, a Loos gauge can help you accurately reproduce that same setting, after working on your mast or shrouds, or after lowering and raising the mast.

Derek Crawford is one of the most knowledgeable C-25 racers that I know, and he uses the Loos gauge to tune his rig. With his permission, I am reproducing his recommendations for tuning with a Loos gauge.

"I've just re-tuned 'This Side Up' for light to moderate air. The Loos gauge reads (just using the FRONT of it - don't bother converting to the back side numbers), aft lowers - 10" of slack (just registers on the gauge), uppers 30, forward lowers 25. The forestay has 10" sag and the backstay a good 6" (when not tensioned). All these are taken with mainsheet, vang and cunningham loose.

The most important parameter of all is to have the mast in column (straight up & down and from side to side) and make doubly sure that the masthead doesn't hook slightly to one side or the other (sight up the mast track to best check this).

With these dialed in you'll be fast to weather and even faster downwind. When the wind kicks up past 15k I put an extra turn on all the shrouds."

Shawn, you asked how much deflection there should be in the headstay. Derek's recommendations are in the first paragraph of his above-quoted discussion. My headstay is so loose that it sways quite freely. I haven't measured the amount of deflection, because I'm still experimenting with it. Derek recommends such large deflections in his headstay and backstay that it takes my breath away, but there's no arguing with success. He's probably right. I just haven't been able to screw up my courage to do it yet. <img src=icon_smile_shock.gif border=0 align=middle> The more deflection, the more the mast can bend. (gulp!)

Steve Milby "Captiva Wind" C-25 T/FK #2554

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Shawn
1st Mate

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USA
62 Posts

Response Posted - 08/10/2003 : 00:22:25

Steve and Dereck,
Thanks for sharing your info. I will try tuning my rig per your specs. I will go in baby steps, as I tend to be very cautious when it comes to keeping my rig upright. But, as I said earlier in this thread, the Cal 227 had their rig unbeleivably loose (to me), so my willingness to play with things has gone way up. Silmarillion is hunkered down for the next couple of months in a hurricane hole (hopefully unneccisairily). When sailing season kicks into high gear again I will try to let you know how things go.
Thanks again for the tips.

Shawn
1980 C25 tr/fk #1960

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Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 08/10/2003 : 12:07:52

Hey shawn,
I was wondering, how did your 25 get to St John's in the first place? Was it sailed there? Come in a container? Beamed down by Scotty?

Are there any other 25's down there?

Frank Gloss
89WK/TR

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Shawn
1st Mate

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USA
62 Posts

Response Posted - 08/13/2003 : 21:41:07

Frank,
I don't know how it got here. I bought her 5 years ago on St. Thomas from a broker. I never met the previous owners. She was in pretty sad shape when I got her, and from studying this site I found out I paid to much for her. But, five years of hard work and more $$'s than I care to think about, she is coming around. She is still probably only worth about as much as I bought her for. But that isn't what it's all about anyway, is it? The times spent sailing with family and friends are priceless. It also gives me a place to be alone with my thoughts and my boat, as well as something to tinker with. Which for me is nearly as fun as sailing her. I hope most sailors think the same way.

Shawn
1980 C25 tr/fk #1960

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