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Shroud Tension

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Mike013
1st Mate

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USA
64 Posts

Initially Posted - 05/01/2007 : 20:56:54

“Ariel” finally made the 375 mile trip from San Diego Bay to her new home on Millerton Lake, north of Fresno. We finally decided to have her hoisted out of the water and placed on her trailer. It was a good thing too, because the trailer pads had to be adjusted to fit the hull. We never would have been able to place her on the trailer without the hoist. I can’t say enough good things about the good folks at Driscoll Shipyard who help us so much.

We were able to launch her with no problems using just the tongue extender that came with the Trail Rite trailer. The ramps at Millerton Lake are long and steep. We put the trailer in the water next to a small dock and I was able to pull her off the trailer and tie her up.

The only snag came when we raised the mast for the first time. In spite of all the warnings on this site, we managed to bend some of the upper shroud hardware during the process.

So I motored “Ariel” over to her new slip and then ordered a new set of upper shrouds from Catalina Direct in Sacramento. We installed the new shrouds with “Ariel” floating in her slip. It took three burly guys to handle the safety lines and we used the mast crutch and mast raising shrouds and mast strap to drop and the raise the mast again.

My question now is just how tight do you rig the shrouds. I tightened them to the specs in my Owner’s Manual but according to my Loos Tension gauge, that only puts about 300 lbs. of tension on the shrouds and the Loos instructions seem to imply that 700 to 800 lbs. is better.

I want to make sure the mast is secured properly before I load the mast with a lot of sail. What is the proper tension for a Catalina 250 upper and lower shrouds and the backstay?

Mike
"Ariel"
2006 C250 WK #859
Central California

Edited by - on

CaptRon400
1st Mate

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USA
90 Posts

Response Posted - 05/03/2007 : 07:17:59

In general, for most sailboats with wire stays and shrouds, 10 to 15 percent of breaking strength is a good starting point. You need a lot of reserve for heavy load conditions, so I would NOT go above 18 to 20 percent. Going below 10 percent may not keep the rig straight at all times. Final tuning should be done on the water in 10 to 15 knots of wind, by "feeling" the tension on both sides. Windward side very taught, leeward slightly slack (but not loose). You should be able to measure and write down these final numbers and then re-use them next year (for a better starting point).

Also, remember that new wire will stretch more than old, so re-meeasure everything in a few months.

Edited by - on

rwbragdon
Deckhand

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USA
20 Posts

Response Posted - 05/04/2007 : 10:44:34

Mike:

Check out this string on tuning the rigging: http://www.catalina-capri-25s.org/forum/topic.asp?ARCHIVE=true&TOPIC_ID=9989&SearchTerms=tune

Edited by - on

Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 05/05/2007 : 10:10:33

Throw away the loose gauge numbers from web sites, books, riggers or any other place they can be found because the 250 isn't typical and those numbers are not suitable to her.

I'm not saying that the guage is worthless... just the numbers you will see out there as applying to the 250.

Here is the deal... the 250 has a very different rig than most of those numbers apply to. The 250 has a modified form of a B&R rig and has no forward lowers. It also has lighter rigging as it is a lightly keeled boat. It is also an open hull without interior bulkheads. The available numbers just don't fit.

The 250 should be tuned firm but not hard, with the upper shrouds (the aft shrouds that go to the spreaders and then on to the mast head) a good bit firmer than the forward (those just below the spreaders).

I know it would be easier if someone could just yield some numbers but first thing to understand is that the loose guages often read very different and there are several differing guages making things even worse. It is better to understand the dynamics of the rig tuning.

What is wanted is a settup that doesn't allow the foresail too much power. To get that the aft lowers should be tuned firm as they are the opposing force to the headstay (though you may be saying...this guy is whacko, the backstay is the opposing force to the headstay... trust me, I'm right about this on the 250.) Tighten them firm but loose enough to allow an inch of deflection when pulling the shroud after grasping it with two fingers at the last finger joints and curling the fingers inward. I know there are those who are thinking this ain't scientific enough... but trust me you will get a feel for it.

The forward lowers should deflect about twice as much as the aft given the same test. If the forwards are tightened too much (equal to the uppers), it will induce reverse (aft) mast bend that is not desirable.

The light rig of the 250 cannot sustain the numbers given for a boat with bulkheads and having a heavy keel and a rig needed to handle a heavy keel.

The last stay to tune is the backstay...tighten it only enough to pull it straight where it won't sag into the sail roach. Do not overtighten the backstay as to do so will release some of the tension on the aft lowers. It is the aft lowers that leverage against the raked spreaders that hold the center of the mast forward so overtightening the backstay reduces the ability of the uppers to hold the center of the mast forward... this is why the 250 is not a candidate for an adjustable backstay tensioner.

If after tuning, one feels that in a breeze the headsail has too much power because of a loose forestay and is sagging off too much...then tighten the uppers a bit more.

A simple test is when running hard to windward in a breeze, the leeward upper shouldn't be shaking but the leeward lower should have some slack. If there isn't any slack... then the lowers may be too tight. If the rig is too tight... light air performance will suffer and if it is too loose, then it can be overpowered in a breeze and suffer too much heel and helm pressure.

Of course it goes without saying when adjusting shrouds to observe symmetry. Once the mast head has been centered using a halyard to the rub rail on each side and the mast column straightness has been set by the lowers... any further adjustment of a shroud has to be countered by an equal adjustment on the other side.

Now...once a settup has been achieved that seems good...then one can use a loose guage and write down those numbers and use them to compare further adjustments and possibly even use them against other similar 250's... but not other boat designs. Keep in mind however that even with the same boat and loose guage... the guages may not read the same.

One final point... the 250 is not typical to heavily keeled boats that need a firm tough rig to handle the sailplan opposing the keel. Those boats will groan and strain under a broach whereas the 250 heels over and rounds up and shakes a broach off like it was no big thing. Many a tradional boat skipper will scoff at the light rigging of the 250 thinking it is dangerous... but it's not true... the rigging is very adequate to the boat design.

I've yet to hear reported to this forum an instance of rig failure from overload on a 250. There have been a couple of failures reported but do to snagging the shrouds on other boats or objects.

Edited by - on

Derek Crawford
Master Marine Consultant

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USA
3312 Posts

Response Posted - 05/05/2007 : 11:15:21

Follow Arlyn's advice guys! He probably knows more about sailing the C250 than Frank Butler himself!

Edited by - on

Bubba
Admiral

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USA
542 Posts

Response Posted - 05/05/2007 : 18:51:26

<blockquote id="quote">quote:<hr height="1" noshade id="quote">To get that the aft lowers should be tuned firm ...
The forward lowers should deflect about twice as much as the aft given the same test.<hr height="1" noshade id="quote"></blockquote id="quote">
I think you mean upper and lower shrouds respectively.
I wish the 250 had split lowers, then maybe we could tune on the fly.

Edited by - on

Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 05/05/2007 : 20:09:25

You're right...that is what I meant to say and I agree that the rig could stand some redesign to enable on the fly rig tuning between light and heavy air. I'm not sure however that a set of forward lowers is the way to go as it is quite beneficial to sheet further inboard and doing away with the forward lowers allows that.

The answer might be diamond uppers where the upper shrouds terminate back to the mast just above the base rather than on the deck. Many designs have used this technique with success and if I'm not mistaken, the new Hunter 25 employs it.

They would set the mast prebend independent of the position of the mast truck so if a backstay adjuster was used to harden the forestay and depower the jib, then the prebend would not be compromised.

Because on such a rig, a backstay tensioner would only depower the foresail, the diamond shrouds could even be fitted with hardening mechanisms to depower the main by adding more prebend.

Edited by - Arlyn Stewart on 05/05/2007 20:12:48

Bubba
Admiral

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USA
542 Posts

Response Posted - 05/06/2007 : 09:26:39

That would be an interesting rig to see, but as you point out, a bit tedious to depower both the headsail and main.

Edited by - on

Mike013
1st Mate

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USA
64 Posts

Response Posted - 05/06/2007 : 10:08:44

Arlyn,

Thanks for the good advice. It was worth waiting for. I'm printing out your reply and placing it in my owner's manual.

Thanks again

Edited by - on

MartinJW
Navigator

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USA
241 Posts

Response Posted - 07/19/2008 : 12:38:19

My dealer set up the rigging tension when we first launched the boat nearly a month ago, but the rigging has naturally stretched and the hull has undergone normal deflection, so the rig needed to be re-tuned.

To do this, I've been following the tuning information from Catalina / U.S. Spars that I received in April 2008. I think that I have the standing rigging tension completely screwed up, and I intend to relieve all the tension and start over using Arlyn Stewart's approach.

However, for whatever it may be worth, here's the most up to date information from Catalina in terms of setting up and tuning the standing rigging for a C-250. (I've attempted to report this verbatim, including possible typos, spelling errors, and incorrect punctuation.)

Rig Set Up and Tuning Guide for U.S. Spars Rig on Catalina 250
...
Once the forestay is attached go around and tighten the other 5 turnbuckles by hand.
...
The mast need a very little rake of 2". You check this using the boom lift halyard with a weight tied to the end and measure at the boom height from the back of the mast to the boom lift halyard. To increase rake you will need to loosen the forestay; to reduce rake you will need to tighten the forestay. If you find that adjusting the forestay is not affecting the rake then you may have the side shrouds too tight which will not allow the mast to move.

Once the rake is set, the mast's pre-bend is now induced. We recommend no more than 1-2" of Pre-bend, this is important to stabilize the center of the mast. The bend is induced by tensioning the cap shrouds and backstay, as the mast bends you may need to loosen the lower shrouds to allow the mast to bend. You use the boom lift in the same way as you did with rake but hold it against the mast at the gooseneck height and look up to the center of the mast and it is here that you are looking for the distance from the back of the mast to the halyard. Without going up the mast, you will have to use sight to establish the bend. Once you have the correct bend, you can take up some tension in the lowers to lock the bend in place. We have made up a simple guide using the Loos gauge that will assist you in tuning the rig.

Rigging tension using the Loos gauge:

Forestay 17%
Cap shroud 15%
lower shroud 15%
Backstay 16%

These numbers are a guide to correct set up, but it is advisable to re-check all of your rigging regularly as tuning is not a one time deal.
...


I'm using the Loos Model PT-1, which - after some linear interpolation between values - converts the listed percentage values as follows:

Forestay (3/16" dia.) 17% = 800 lb (n/a to PT-1 model)

Upper Shroud (5/32" dia.) 15% = 510 lb = 35.8 PT-1 scale value
Lower Shroud (5/32" dia.) 15% = 510 lb = 35.8 PT-1 scale value
Backstay (5/32" dia.) 16% = 550 lb = 36.5 PT-1 scale value

I hope that this information is, somehow, helpful.

Edited by - MartinJW on 07/19/2008 15:47:29

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 07/19/2008 : 13:47:36

I noticed at the Miami Boat show that the 2008 model has different spars (mast and boom) and spreaders from out 2005 model.
The book is quite different particularly near the topping lift end.
The mast is different in profile and the spreaders appear much smaller.

All of these things probably indicate different tensions from those illustrated for the 2008 model.

I like Arlyn's approach.. Logical!

Paul

Edited by - on

MartinJW
Navigator

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USA
241 Posts

Response Posted - 07/19/2008 : 15:51:24

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by britinusa
 I noticed at the Miami Boat show that the 2008 model has different spars (mast and boom) and spreaders from out 2005 model.
The book is quite different particularly near the topping lift end.
The mast is different in profile and the spreaders appear much smaller.

All of these things probably indicate different tensions from those illustrated for the 2008 model.

I like Arlyn's approach.. Logical!

Paul
<hr height="1" noshade id="quote"></blockquote id="quote">

Yes, apparently starting with the 2008 models, the C-250 mast and boom are now being made by U.S. Spars (of Florida).

Edited by - on

Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 07/19/2008 : 16:30:38

My advice. Put away the Loos gauge (I did mine) and go with Arlyn's tuning recommendation. I set my uppers to be very tight and with a two-finger pull at shoulder height (the fingers, inside of first knuckle, not your arm pulling) the deflection is 1". Lowers are looser and deflect 2"-3" inches. My leeward lowers are often loose when sailing. I am very happy with the performance of this setup. The backstay does almost nothing on our rigs.

Edited by - Nautiduck on 07/19/2008 16:31:45

MartinJW
Navigator

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USA
241 Posts

Response Posted - 07/19/2008 : 17:43:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Nautiduck
 My advice. Put away the Loos gauge (I did mine) and go with Arlyn's tuning recommendation. I set my uppers to be very tight and with a two-finger pull at shoulder height (the fingers, inside of first knuckle, not your arm pulling) the deflection is 1". Lowers are looser and deflect 2"-3" inches. My leeward lowers are often loose when sailing. I am very happy with the performance of this setup. The backstay does almost nothing on our rigs.
<hr height="1" noshade id="quote"></blockquote id="quote">

Randy,

Are you getting about 2" of rake and about 1-2" of mast bend?

(I'm cranking the upper shrouds and backstay to no avail - I think that I have NO mast bend right now.)

Thanks,
Martin

Edited by - on

Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 07/20/2008 : 10:47:35

I have about 3" of mast rake.

Forgot another point. Forget pre-bend (mast bend). With our rigging/tuning, pre-bend is a myth IMHO. The shrouds control it, not the backstay. If you get the uppers tight enough to bend then the lowers are too loose. Tighten the lowers up and bye bye to the pre-bend. The lowers pull the middle of the mast back. That is the challenge of our rigs, all of the shrouds (and the backstay) pull back. The point of keeping the lowers looser than the uppers is to actually prevent reverse-bend (not a good thing). Your mast being straight is fine.

My advice to tuning the rig is:

Get the boat level on her lines
Loosen all shrouds.
Using the forestay and backstay induce 3-4" of mast rake.
Using the uppers, get the mast in column port-to-starboard (firm, not tight).
Get all shrouds firm, staying in column. (from now on adjust both sides evenly)
Tighten the uppers so that you can deflect the shrouds 1" with two fingers at shoulder height.
Tighten the lowers so that you can deflect the shrouds 2-3" with two fingers at shoulder height.
Go sailing.

You can make yourself crazy tuning this rig because every time you tighten a shroud it changes the relationship of the other shrouds. Keep it simple. Follow Arlyn's advice. I will post in the next Reply the text I found from Arlyn in the archives. It is the basis for how I tune my rig.

Edited by - Nautiduck on 07/20/2008 10:56:52

Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 07/20/2008 : 10:52:34

Here is the text from an Arlyn post on tuning. Note when he says "aft lowers" that is what I call the "uppers." For Arlyn, the uppers end at the spreaders and then become the "aft lowers." When he says "forward lowers" that is what I call "lowers"

"The 250 has a very different rig than most. The 250 have a modified form of a B&R rig and have no forward lowers. It also has lighter rigging, as it is a lightly keeled boat. It is also an open hull without interior bulkheads. The available numbers just don't fit.

The 250 should be tuned firm but not hard, with the upper shrouds (the aft shrouds that go to the spreaders and then on to the mast head) a good bit firmer than the forward (those just below the spreaders).

I know it would be easier if someone could just yield some numbers but first thing to understand is that the loose gauges often read very different and there are several differing gauges making things even worse. It is better to understand the dynamics of the rig tuning.

What is wanted is a setup that doesn't allow the foresail too much power. To get that the aft lowers should be tuned firm as they are the opposing force to the headstay (though you may be saying...this guy is whacko, the backstay is the opposing force to the headstay... trust me, I'm right about this on the 250.) Tighten them firm but loose enough to allow an inch of deflection when pulling the shroud after grasping it with two fingers at the last finger joints and curling the fingers inward. I know there are those who are thinking this ain't scientific enough... but trust me you will get a feel for it.

The forward lowers should deflect about twice as much as the aft given the same test. If the forwards are tightened too much (equal to the uppers), it will induce reverse (aft) mast bend that is not desirable.

The last stay to tune is the backstay...tighten it only enough to pull it straight where it won't sag into the sail roach. Do not over tighten the backstay as to do so will release some of the tension on the aft lowers. It is the aft lowers that leverage against the raked spreaders that hold the center of the mast forward so over tightening the backstay reduces the ability of the uppers to hold the center of the mast forward... this is why the 250 is not a candidate for an adjustable backstay tensioner.

If after tuning, one feels that in a breeze the headsail has too much power because of a loose forestay and is sagging off too much...then tighten the uppers a bit more.

A simple test is when running hard to windward in a breeze, the leeward upper shouldn't be shaking but the leeward lower should have some slack. If there isn't any slack... then the lowers may be too tight. If the rig is too tight... light air performance will suffer and if it is too loose, then it can be overpowered in a breeze and suffer too much heel and helm pressure.

Of course it goes without saying when adjusting shrouds to observe symmetry. Once the masthead has been centered using a halyard to the rub rail on each side and the mast column straightness has been set by the lowers... any further adjustment of a shroud has to be countered by an equal adjustment on the other side.

Now...once a setup has been achieved that seems good...then one can use a loose gauge and write down those numbers and use them to compare further adjustments and possibly even use them against other similar 250's... but not other boat designs. Keep in mind however that even with the same boat and loose gauge... the gauges may not read the same.

One final point... the 250 is not typical to heavily keeled boats that need a firm tough rig to handle the sail plan opposing the keel. Those boats will groan and strain under a broach whereas the 250 heels over and rounds up and shakes a broach off like it was no big thing. Many a traditional boat skipper will scoff at the light rigging of the 250 thinking it is dangerous... but it's not true... the rigging is very adequate to the boat design.

I've yet to hear reported to this forum an instance of rig failure from overload on a 250. There have been a couple of failures reported but do to snagging the shrouds on other boats or objects."

Edited by - Nautiduck on 07/20/2008 10:52:57

MartinJW
Navigator

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USA
241 Posts

Response Posted - 07/20/2008 : 19:28:19

So I essentially followed Arlyn's and Randy's procedure, and THEN I checked tensions with the Loos gauge. Here's what I have right now:

Backstay = 20 (Loos PT-1 scale) = 140 lbs
Upper Shroud, Port = 29 = 320 lbs
Lower Shroud, Port = 16 = < 140 lbs
Upper Shroud, Starboard = 30 = 335 lbs
Lower Shroud, Starboard = 24 = 200 lbs

It looks like the lower shrouds need a little adjustment to at least bring them closer to the same values. (I'll probably back off the starboard side.)

Here are the potentially BIG problems, as near as I can tell:

#1. In the water - in which the boat isn't perfectly level, I'm sure - the mast appears to have about 15" (estimated) rake when measured at boom level. I think that this is WAY off.

#2. The mast appears to have a very slight bend FORWARD. That is, the middle of the mast seems to be flexed slightly towards the bow. This may be an optical illusion, but I think this is the case. No amount of loosening of the lower shrouds and/or tightening of the upper shrouds will induce a proper pre-bend.

#3. The tension rods in the cabin (that appear to transmit the tension from the on-deck plate to the hull) are not tight at all. In fact, one can easily wiggle them.

Here are some questions about this situation:

Q1: Is there a turnbuckle on the forestay? (My boat has roller furling, and I can seem to find a way to easily inspect the lower end of the forestay.) It seems like the forestay has to be shortened substantially to correct the excess rake (and then I'll need to re-tune the entire rig).

Q2: Should the tension rods in the cabin be tight when the boat is at rest?

(By the way, the rigging on my Capri 16 and Catalina 18 was the same configuration as the C-250; I'm fairly conversant in getting the right amount of mast rake and mast pre-bend with this setup. Right now, however, I'm stumped.)

Any thoughts, suggestions, comments are welcomed!

Thanks,
Martin

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