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Old 03-06-2017, 08:24   #1
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Shroud tension on a cat

Beginner sailor here. We were sailing a 38 foot cat (2008 lagoon) on a close reach in 15-18 kts winds & small waves. We tried full sail and 1 reef on the main, in both cases the leeward shroud was completely loose (tripod rig). The ASA 114 book talks about signs of the a cat being overpowered, one of them being leeward shroud loose, the others being more wake behind leeward hull and weather helm. We didn't have weather helm but we did have more wake behind the leeward hull. Given the conditions I wouldn't think this was the case, but I was surprised how loose the shroud was. Should we have been looking to depower the sails? We were getting about 6-7 kts (GPS), so nothing wild.
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Old 03-06-2017, 09:07   #2
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Re: Shroud tension on a cat

You perhaps should have been thinking about depowering, but no you weren't overpowered. And any time you're saiing to weather at more than a few knots, you'll have more wake from the leeward hull. So, yes, the rig's a bit loose.
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Old 03-06-2017, 18:57   #3
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Re: Shroud tension on a cat

What is completely loose? Do you mean it was not tensioned slightly or very slack?

Before two years ago, in high winds and stress, my leeward shroud would pump. I had a lot of word done to the standing rigging and afterwards it is tighter, but still slack in heavy winds. I think if you tighten it too much you risk putting the foot of your mast through the bottom of the boat.
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Old 05-06-2017, 15:13   #4
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Re: Shroud tension on a cat

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What is completely loose? Do you mean it was not tensioned slightly or very slack?
It was very slack - like a loose wire, it was just flopping in the wind. It looked like it had a foot or more of slack.
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Old 05-06-2017, 15:46   #5
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Re: Shroud tension on a cat

That sounds way to loose. I'd suggest having it tightened. I'm not a professional at this so can't tell you how. Maybe you should ask a moderator to move this thread to the Lagoon or catamaran forum.

Welcome to the forum btw.
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Old 05-06-2017, 15:58   #6
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Re: Shroud tension on a cat

A tripod rig is completely different from a mono in terms of rig tension. Yes, at rest and in light winds the lee shroud should have some tension on it, but it is completely normal for the shroud to go slack when pressed. Unlike a mono, the mast does not depend on shroud tension to stay in column--that is what the diamond wires and other braces are for. What Palaran said; do NOT over tension.

Additionally, a mono depends on the backstay for forestay tension when beating. On a tripod-rigged cat, forestay tension comes from mainsheet tension, not backstay tension, so the rules for driving to windward are a little different. This article should give you some tips:

Sail Delmarva: Driving to Windward...

As for how to sail a cat, the best way to learn is on a beach cat, but I guess we missed that opportunity. The reason is that you can explore the edge of the develop and learn the feel of the wind and boat. That is hard to develop on a big cat.

Yes, one indication of when you are over powered is when the windward wake becomes less. But it is normal for there to be some difference. Angle of lean is a factor (not a lot of lean, but some), but this is affected by waves as well. The final rule for a beginner (and for rest of us as well) is to be VERY mindfull of sailing downwind with more sail than you can carry to windward. Remember also that cats reef for the gusts. This means that the best strategy, for now, is to drop all sail around squalls, because you don't know whether they are holding a good breeze or a hurricane-force down draft.

I'd get some books on sailing beach cats and read those. The rules, regarding being over powered, are the same.
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Old 05-06-2017, 16:20   #7
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Re: Shroud tension on a cat

Get yourself a GOOD rigger..

If you can't, then get yourself a loos guage for your wire size. Use the guage on the front to tighten to the correct values.


After we replaced our rigging and were dropped in the water we needed to retighten our rigging. On one passage (before tuning) with big waves (12ft) and biggish wind (25knot) our inner and outer shrouds almost slapped each other on the lee side. We got a loos guage and retuned (tightened and made sure the mast was straight and raked properly). After that we have never had a problem. They get a little looser on the lee side on a good beam reach but not sloppy! Just loose enough you can feel the difference between the 2 sides (If that helps).
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Old 05-06-2017, 17:48   #8
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Re: Shroud tension on a cat

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Get yourself a GOOD rigger..

If you can't, then get yourself a loos guage for your wire size. Use the gauge on the front to tighten to the correct values.
Given the variable flexibility of catamarans, Don't put too much faith in a number. Tuning a tripod rig is COMPLETELY different than tuning a typical fore-aft rig on a monohull. Even if you hit the numbers, when a cat torques in the waves, the values will change. It's nice if they don't get loose, since impact loads are less, but most will when the boat is really powered up. In 10 knots, maybe not. But it has at LEAST as much to do with the hull design as the rig, so you MUST consult the boat designer as well as the rigger.

Just sayin'. All I've sailed for 35 years is cats, all types.
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Old 06-06-2017, 10:01   #9
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Re: Shroud tension on a cat

What thinwater said. (Both Times)

I never understand it when people suggest that a leeward stay is too loose on a cat, why does it need to be tight? It ain't doing anything. Having said that I do have some shock cord straps on all my boats to stop some of the annoying slapping
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Old 06-06-2017, 11:01   #10
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Re: Shroud tension on a cat

Why not add a set of runners to aide in tensioning the forestay? It's commonly done/the norm on fractionally rigged mono's. And the force vector that they create would be more in line with the headstay then the one from the fixed shrouds.
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Old 06-06-2017, 11:41   #11
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Re: Shroud tension on a cat

Cause the main provides that tension particularly with the appropriately bendy mast and appropriate mast rake. Look up the mast from the base, It should be a slight banana shape and their should be maybe 4 degrees of rake dependant on design and application. A dead straight stick has no place on a decent multi
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Old 06-06-2017, 11:55   #12
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Re: Shroud tension on a cat

Runners allow you to tune headstay tension independent from main sail trim. At least on many designs. And while yes, the whole sail plan needs to be tuned to work together synergistically, this can at times best (or only) be achieved by seperate tuning controls.


Since if/when you depower the main by easing the traveler & sheet, if leech tension is what was providing headstay tension, you've now just powered up the jib via slackening the headstay. Non? As the jib's draft will now be much, much fuller. Increasing your heeling moment, leeway, & drag (from the sail). Which, when the jib is quite full, often one has to overtrim the main a bit in order to compensate for this. And then you wind up going in a bit of a circle trying to sort out which is the most important/where the correct balance lays. Causing a lot of compromise that might be removed by adding runners.
Just a think.
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Old 06-06-2017, 11:56   #13
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Re: Shroud tension on a cat

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Why not add a set of runners to aide in tensioning the forestay? It's commonly done/the norm on fractionally rigged mono's. And the force vector that they create would be more in line with the headstay then the one from the fixed shrouds.
The difficulty is that the main carries so much roach that runners that are angled back far enough to do any good at all are in the way as soon as the main twists at all. If I raced I would add Dyneema runners. For the reason you suggested.

That said, runners are used to support the upper portion of the mast if the cat is fractionally rigged and has a masthead reacher. But the purpose is not to tension the working forestay.

The answer is mainsheet tension. This is also one of the reasons the boats often carry a smaller jib; it's difficult to carry enough forestay tension for a masthead genoa.

Every rig has trade offs. The main reasons cats got away from masthead, conventional rigs are:
  • No keel to tension the backstay against. The strain on the main crossbeam is already major.
  • For beach cats, the ability to finely control healing force. They are fastest when sailed with one hull just out. OF course, this does not really apply to larger cats... much.
  • The ability to control heel by feathering. Even a "cruising cat" if driven hard, needs to bleed power by feathering in the gusts. This works best with a large main and full battens. Remember that a cat cannot allow anything like a knock-down.
There are cats that carry more conventional rigs. The PDQ 36 is one, with inboard shrouds, a genoa, and runners to the transoms. As a result, the rig tunes more like a conventional masthead rig. This can make a lot of sense, depending on the design of the cat.



The point is that a different rig design requires different tuning, not because it is a cat, but because the rig is different.
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Old 06-06-2017, 12:13   #14
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Re: Shroud tension on a cat

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The difficulty is that the main carries so much roach that runners that are angled back far enough to do any good at all are in the way as soon as the main twists at all. If I raced I would add Dyneema runners. For the reason you suggested.
How do runners get in the way of mainsail twist? They're on the weather side of the sail when tensioned.

That said, runners are used to support the upper portion of the mast if the cat is fractionally rigged and has a masthead reacher. But the purpose is not to tension the working forestay.
Understand. And yes, what will work (or work best) depends entirely on the design of the rig. Albeit some boats (racers usually) have runners both for tensioning the headstay (jib), & a way to tension the masthead for use with reachers (acting as masthead backstays).

The answer is mainsheet tension. This is also one of the reasons the boats often carry a smaller jib; it's difficult to carry enough forestay tension for a masthead genoa.
True enough.

Every rig has trade offs. The main reasons cats got away from masthead, conventional rigs are:

No keel to tension the backstay against. The strain on the main crossbeam is already major.

- For beach cats, the ability to finely control healing force. They are fastest when sailed with one hull just out. OF course, this does not really apply to larger cats... much.

- The ability to control heel by feathering. Even a "cruising cat" if driven hard, needs to bleed power by feathering in the gusts. This works best with a large main and full battens. Remember that a cat cannot allow anything like a knock-down.
This kind of goes without saying regarding knockdowns. And full battens allow for a lot more "gears" when it comes to trimming than do conventional length battens. That's been apparent for me at least, since I started racing in the early 80's.

There are cats that carry more conventional rigs. The PDQ 36 is one, with inboard shrouds, a genoa, and runners to the transoms. As a result, the rig tunes more like a conventional masthead rig. This can make a lot of sense, depending on the design of the cat.


The point is that a different rig design requires different tuning, not because it is a cat, but because the rig is different.
Just trying to point out other options. And it's good to discuss them like this in order to clarify things.
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Old 06-06-2017, 12:32   #15
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Re: Shroud tension on a cat

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Just trying to point out other options. And it's good to discuss them like this in order to clarify things.
The windward runner is not in the way, but the leeward one needs to be released. If left too loose they catch on batten tips. They are also in the way around the transom, since all boarding on most cats is via the sugar scoops.

Just one more thing, that's all. I've considered them on my current boat, but never did. I had them on my last cat, and they helped.
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