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Catalina/Capri 25/250 Sailor's Forums

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Lwr shrouds tension

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Esteban
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139 Posts

Initially Posted - 01/10/2006 : 20:15:10

Question on lwr shroud tension:

I've noticed that with a 20-25 degree list, the leeward lwr shourds will slacken just a bit (still look straight as an arrow) but you can visibly note it. Mind you, they are not flopping in the wind - you can just see them loose a little stiffness. The upper shroud stays completely still.

Some folks tell me this is normal and that I actually have a bit of a stiffly tuned rig.

I had the marina tune the rigging one year and saw the same thing. I haven't measured shroud tension - mostly because I don't have a numbers to compare this too.

I witnessed an Island Packet limp back into the marina this fall with half a mast and a big mess. It really got my attention.

Asking for some thoughts on this. Thanks.

Esteban

Esteban Diaz
Tally Ho!

Edited by - on

ClamBeach
Master Marine Consultant

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Response Posted - 01/10/2006 : 21:04:50

Sounds ballpark right to me. Leewards should go slightly loose when the sails are under 'pressure'... aft lowers are usually set a little looser than the forward lowers so you can tweak a little mast bend in with the adjustable backstay.

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 01/10/2006 : 21:35:34

If it takes 20 degrees of heel and they still don't wave in the wind, you are indeed on the tight side, which is fine if they behave the same on both tacks. That's a "cruising tune." Any Island Packet is rigged so much more heavily than a C-25 that whatever happened is probably not relevant to you--maybe he hit a bridge.

Edited by - on

Frank Hopper
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Pitcairn Island
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Response Posted - 01/10/2006 : 21:44:23

I fly a tight rig, heavy wind makes me more comfortable that way.

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Champipple
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Response Posted - 01/10/2006 : 23:09:09

You should be okay, especially with the lowers. When your close hauled, get someone else to take the tiller and take a look up the mast. The slack is normal, but even with it, the tip of the mast should still be straight and the center shouldn't flex out or sag in.

Duane

Edited by - on

Ben
Master Marine Consultant

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1234 Posts

Response Posted - 01/11/2006 : 07:27:10

My situation is the opposite. My leeward shrouds are slack as I'm sailing. Have I been operating in an unsafe manner?

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Frank Hopper
Past Commodore

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Pitcairn Island
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Response Posted - 01/11/2006 : 07:33:23

Several issues Ben,
Have you swagged your uppers to the spreader caps? If so then you are protected from the slack letting the upper move off the spreader which would probably bring down your rig when you tacked. What is your typical wind range? If I ran a loose rig in my typical wind ranges I would see back slap of my mast as I pound through the chop. The Loos people believe that tight rigs spread the load to more points and it reduces the odds of a hardware failure.

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atgep
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Response Posted - 01/11/2006 : 07:57:53

Don't forget the design of our boats. It is only possible to get so much tension on the lowers before the deck starts to flex as there are no bulkhead to spread the load.

Tom.

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Steve Milby
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Response Posted - 01/11/2006 : 08:17:38

The manner in which you should tune your rig depends on whether or not you have a backstay adjuster.

If you don't have a backstay adjuster, then generally, you want all the shrouds to be tensioned so that the leeward ones relax very slightly when the boat is beating to windward in about 12-15 kt. winds.

If you have a backstay adjuster, and tension the rig in the manner described above, then the backstay adjuster won't work. The purpose of the adjuster is to bend the mast when you put tension on it, and adjusting the rig in the manner described above will prevent the backstay adjuster from bending the mast. Bending the mast pulls the fabric in the middle of the mainsail forward and flattens the sail. It also increases the tension on the headstay, depowering the jib and helping the boat point to windward. When sailing downwind, you can release the tension on the backstay adjuster, allowing the headstay to go slack. A slack headstay powers up the rig when you're sailing off the wind. In order for the backstay adjuster to work, the aft lowers need to be loose enough so that they allow the mast to bend, but tight enough so that they prevent it from bending too far.

You can find instructions for tuning both types of rigs in an article I wrote that is posted in the racing section of the home page. Rig tuning is discussed on the eighth page of the article.

Edited by - on

Ben
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Response Posted - 01/11/2006 : 11:01:50

Thanks ya'll.

Answering Frank first, by swagged do you mean tied off to the spreaders? If so, then yes. My shrouds are made fast (proper terminology?) to the spreaders with wire.

Answering Steve, while I now have a backstay adjuster, last season I did not. I will be sure to print out and take on the boat the article you wrote.

Thanks so much everyone. I'm glad my rig didn't come down this year!

Edited by - on

Esteban
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139 Posts

Response Posted - 01/11/2006 : 12:07:08

Thank you one and all - it sounds like doing okay. Guess I should start playing with the split backstay adjuster. Thanks again!

Esteban

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Dave Bristle
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Djibouti
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Response Posted - 01/11/2006 : 22:27:08

I'm suspicious there's one slight misunderstanding here... IMHO, the leeward upper shroud should be tight at all times, and does not affect bending the mast since it essentially follows the bend via the unraked spreaders. The aft lowers indeed should be a little loose in order to use the backstay to bend the mast. If Ben's leeward upper is loose, I'd tighten the upper shrouds. But I could be all wrong.......

BTW, I've been told that if a boat is regularly on a mooring (rocking back and forth), the rig should be relatively tight so that it doesn't create shock loads on the chainplates and swages.

Edited by - Dave Bristle on 01/11/2006 22:32:38

Steve Milby
Past Commodore

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5853 Posts

Response Posted - 01/12/2006 : 07:38:09

The loosest shrouds I've ever seen were on the boats used for teaching at Annapolis Sailing School in St. Petersburg, FL. years ago. They were so loose that they were all waving freely, even at the docks, with no load. If they're that loose, they can fall out of the spreader caps, unless they're held in the spreaders with wire. If they come out when the rig is under high load, the mast will come down. The uppers were wired in at Annapolis SS.

I like to see them adjusted so that the tension on the leeward uppers just begins to relax when beating to windward in 10-15 kt. winds. If the leeward uppers relax very slightly, that tells you that they aren't overly tight. If you tighten them so that they never relax at all, then you can't tell if they're overly tight by a little or by a lot. If they're overly tight by a lot, you can damage the boat structurally. They should never be so loose that the rig slaps back and forth as the boat tacks. When they're that loose, just imagine the stresses on the chainplates when the whole rig repeatedly slaps back and forth, and is jerked to a sudden stop by the steel shrouds. When I say the leeward uppers should relax slightly, that doesn't mean that they should wave freely. You should just be able to see the tension on them relax, even though the shroud still looks straight.

Edited by - on

ClamBeach
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Response Posted - 01/12/2006 : 22:53:57

>"I like to see them adjusted so that the tension on the leeward uppers just begins to relax >when beating to windward in 10-15 kt. winds"

I'm with Steve on this one... I look for slightly loose on the leeward side when the rig is being moderately loaded.

Edited by - on

JimB517
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Response Posted - 01/13/2006 : 19:31:31

my leeward shrouds flap like overcooked spagetti when beating to windward at 15 knots of wind. This has not been a problem. Gary Norgans are much looser than mine.

Hauling on the backstay adjuster tightens them up a little. I've tried to follow Steve Milby's tuning guide, it's not easy. I can bend the mast quite a bit, though. Gary and I just re-tuned using his Loos gage. With backstay tension in the middle, my forestay is 50, uppers are 30 and both lowers are 25. He is about 10 lower on everything. My mast has a slight bow at the spreaders. Hauling tight on the backstay, I can move the masthead back about 6 inches.

Don't worry about it, you are rigged tight and sounds just about right for a non-racer.

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Steve Milby
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Response Posted - 01/13/2006 : 21:19:03

Jim, you sail your boat in all conditions and, more than most of us, you really need your rig to be tuned just right.

For years, I allowed my leeward stays to be loose in medium winds, and eventually realized that it's best to adjust almost all of that slack out of the stays. I first realized it when I was sailing in choppy seas and strong winds, and heard a loud metallic banging in the boat. I eventually figured out that the noise was from the whole rig slamming back and forth, and I believe the rig would even jump occasionally, when the boat suddenly dropped out from under the mast, into a trough. If the stays are snugged down, the rig won't move around like that.

Also, the forward lowers need to be snugged down the most. When you put tension on the backstay adjuster, you don't want the whole mast to tilt aft. You only want the upper half of it to bend back. The chainplates for the forward lowers are forward of the base of the mast. When you pull on the backstay adjuster, the forward lowers resist that pull, and hold the lower half of the mast in place, so that it can't lean back. If the forward lowers are too loose, then the whole mast tilts back instead of just bending back the part of the mast above the spreaders. If you tilt the whole mast aft, you do the exact opposite of what you want to do. Tilting the mast aft increases weather helm at a time when you need to reduce it. If, instead, you bend back only the upper half of the mast, that pulls the headstay taut, pulls the fabric in the middle of the mainsail forward, and flattens both the jib and the mainsail, all of which help reduce weather helm.

Why don't you try snugging up the stays all around, but especially the forward lowers, so that the mast can't move around so much when the boat is pitching and rolling. Then loosen the aft lowers completely. (Do this while you're at the dock.) Then pull down your backstay adjuster until the top of the mast bends aft about 6-8". Then adjust the aft lowers so that they are just snug. When you release the backstay adjuster, the aft lowers should become slightly looser. The purpose of the aft lowers is to prevent the mast from being bent any farther than that 6-8". By adjusting the aft lowers looser or tighter, you can increase or decrease the amount of bend in the mast. The looser they are, the more the mast will bend. Some racers keep them very loose all the time so they can really bend the mast, but that defeats the purpose of the aft lowers, to protect your mast from bending too far.

When the backstay adjuster is eased, the headstay should be very slack. When the backstay adjuster is fully tensioned, the headstay should have no sag. The amount of sag in the headstay also limits the amount that the mast will bend. If there's a lot of sag, then when you put tension on the backstay adjuster, the mast will bend back farther before the headstay becomes taut.

Edited by - Steve Milby on 01/13/2006 21:27:50

JimB517
Past Commodore

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USA
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Response Posted - 01/15/2006 : 21:49:13

I'll try it Steve, I also want to post a photo of the bow in the mast. I'm worried about it. May be an optical illusion. Tomorrow is my day off (Monday). I'm sailing and also I'll take the photo.

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Esteban
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Response Posted - 01/15/2006 : 22:02:37

This I gotta see Jim!

I've never played much with my backstay adjuster. From the sounds of everyone's input maybe my rig is well tunned.

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Esteban
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Response Posted - 01/15/2006 : 22:04:23

Another question just popped up - how do I measure forestay tension with a furler? No can do?

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Steve Milby
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Response Posted - 01/17/2006 : 12:36:23

<blockquote id="quote">quote:<hr height="1" noshade id="quote"> Another question just popped up - how do I measure forestay tension with a furler? No can do?<hr height="1" noshade id="quote"></blockquote id="quote">
Whether you have a furler or hanked-on sails, generally there’s no reason why most of us should measure headstay tension at all. There is no specific amount of tension that is right for all boats in all conditions. If you sail in strong winds, like on San Francisco Bay, then you should put a little extra tension on your headstay. If you sail on the Chesapeake Bay, which tends to have lighter winds on average, then you should ease the headstay tension slightly. If someone tells you what tension they use on SF Bay in winter, and you use it on your boat on the Chesapeake in mid-summer, it will probably be all wrong. That’s why I have little use for a Loos gauge, unless you’re a very high-level racer, or unless you sail a popular race boat, for which someone has worked out a whole range of recommended tensions for a variety of conditions. I don’t know of anyone who has done that for a C25. Many one-design racers just set the shroud tensions on their boats at the tensions recommended on their website, and leave them at that setting all year around. The recommended tensions that come with a Loos gauge aren’t even specific to our boats. They’re just ball-park estimates that someone thinks are okay for most boats in average conditions.

Instead of thinking about Loos gauge tensions, you should be thinking about sail shape and boat performance. If you don’t have a backstay adjuster, the headstay should not be bar-tight, but it should have very little sag. If you sail in an especially windy venue, you should probably put an extra turn or two on the headstay turnbuckle. In a light-air venue, you should back the turnbuckle off a turn or two. After you tune the rig, sail the boat and look at the sail shape. If the jib is too baggy or if the headstay sags too much under sail, then adjust the headstay turnbuckle accordingly. If you can find another C25 to act as a tuning partner, you can find out whether you can point at least as high and maintain at least the same speed as he. If not, you might be able to improve it by making some adjustments. In short, tune the rig so that the boat performs the way you think it should. Performance is what really matters, and not an arbitrary number of pounds of tension.

An adjustable backstay allows you to tighten up the headstay while you're underway when you sail to windward in moderate or stronger winds, and to loosen your headstay and make it sag when you want to sail in lighter air or off the wind. Thus, a well-tuned rig with an adjustable backstay will have a shocking amount of headstay sag when the tension is completely released, but it will have very little sag when it is fully tensioned. Accordingly, there’s no specific amount of headstay tension recommended for a boat with an adjustable backstay. The whole point is to be able to make big adjustments in its tension.

Whether you have a furler, or hanked-on sails, just tune the rig for good sail shape and peak performance.

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Esteban
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Response Posted - 01/17/2006 : 21:58:29

Thanks Steve - that makes good sense and rids that nagging question in the back of my head.

My first year sailing was without a furler, and I got very used feeling the headstay tension by hand on my little pre-sail inspection. My second year I sailed with a furler and having that extrusion on the headstay kind of threw off my feel for the tension. Off course, as I got braver at sailing in bigger winds 20-25 and started to get more fussy about sail shape and trim I've gotten a little more critical about the movement on lwr leeway shourds when really healing over.

From the sounds of everyone's advice it looks like I'm not far off the mark and I can play a little bit with the tunning to see what works best. The insight on using the backstay adjuster for wind conditions makes a great deal of sense - probably more so than what it will do to the main sail shape. Just seeing that demasted Island Packet that really got me thinking... Thanks.

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