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Shroud tension query

kbgunn

.
Sep 19, 2017
145
2006 Hunter 38 4410 Lake Lewisville, TX
I've been working on getting the rig tuned and have made some good progress but I still have one issue. I have a Catalina 30 Tall rig with bowsprit. I have the mast in column and centered, no significant prebend for the masthead rig.

I've tightened the upper and lower shrouds port and starboard to the following.
Uppers with 1/4" 304 1x19 stainless cable with breaking strength assumed 8200#- adjusted to 1100# or 16% BS (36 on the Loos gage)

Lowers with 3/16" 304 1x19 stainless cable with breaking strength assumed 4700# -
adjusted to 770# or 16% BS (23 on the Loos gage)

Went out in about 9kts with full main and 135% genoa. On port tack, windward and leeward shrouds all look good with no slop. On starboard tack, the leeward lowers are visible slack and floppy.

My question is, do I continue to crank the port shroud turnbuckles? Is there some other interplay going on which I'm not familiar with? it's curious starboard is fine with only port slack on a starboard tack.

Thanks,
KBG
 
May 12, 2004
1,320
Hunter Cherubini 30 New Port Richey
It think it may be easier to tuna fish then to tuna rig. Over the 21+ years I've owned Fraulein II, I've been tinkering with the shroud tension. A half turn here, a half turn there.:banghead: Maybe one day I will get it perfect. But most days I just wanna sail.
 
Oct 26, 2010
1,405
Hunter 40.5 Beaufort, SC
Is your mast a Selden? Google the Selden rig tuning guide. If you can't find it pm me with your email and I will send you a PDF file. I have a swept back fractional rig with backstay and they say to tension the cap shroud to 25% initially :yikes:. Seems tight to me but that is the spec.
 
Feb 26, 2004
21,892
Catalina 34 224 Maple Bay, BC, Canada
The C30 boat manual has a great tuning guide. All masthead Catalinas do.
 
Oct 19, 2017
6,875
O'Day 19 Littleton, NH
Tell a little about your boat. New, late model, older? This is your first time sailing her? It sounds like you might have aging stays and one side, either the uppers (cap shrouds), or the less react to tension unevenly. Is it possible one side is shorter than the other? You checked for plumb using the halyard with a weight at the gooseneck?
Your spreaders are even and at the same angle?

-Will (Dragonfly)
 

MitchK

.
Sep 22, 2017
102
Capital Yachts Newport 28 Burbank, WA
I don't have very much experience with tuning the rigging on a sailboat. I have been working on tuning the rigging on my Newport 28, so I have some understanding. Before I took my mast down for overhaul, I used a Loos gauge to measure the tension. Now this tension was set up by the previous owners, so I do not know if it is correct or not. I do have substantial experience in erecting guyed towers. I have lost track of how many I have worked on over the years. Now in that type of rigging which is very similar in function to a sailboats rigging, pretty much all guyed tower manufactures specify 10% of the guy wire rating. So if your shrouds are tensioned at 16%, I would think that they are too tight, and should be relaxed. When I measured the rigging on my boat before I took it down, all of the rigging except the fore and aft stays were right at 8%-10% of the wire diameter rating. Now that is my limited experience, so take it with a grain of salt. So if it were me, I would start around the 10% range and adjust from there.
 

Joe

.
Jun 1, 2004
7,409
Catalina 27 Mission Bay, San Diego
Tune it with out the gauge, using one of the many mast tuning guides out there. There's a good one on the C&C owner's site. www.cncphotoalbum.com. After it's set up correctly, use your Loos gauge to record the settings.
Use the settings as reference when occasionally checking the rig tension.
 
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Likes: Will Gilmore
Oct 26, 2010
1,405
Hunter 40.5 Beaufort, SC
:plus:
Get it all in alignment, plumb, with desired rake, and straight. Relying on gauges ignores that goal.

-Will (Dragonfly)
+1 on the Will's statement and I assume he means that condition when sailing in a stiff breeze. I wouldn't go buy a guage to rely on it soley for tuning but if you have one, why not use it? Agree with Will, the goal is desired rake, straight, and plumb with enough tension to hold the mast that way in sailing condition. For me with a backstay, fractional rig and two swept back spreaders the tension is surprisingly taught per the Selden tuning guide. In fact it says the thing to do is set the rake, the bend, and get it plumb and straight with only a little tension. Then tension to the specs, keeping it plumb going back and forth from side to side and making sure its plumb and straight. Then you untension the backstay and make sure the cap shroud tension doesn't go above 25%. (For 3/8 inch wire that's pretty tight!) then re-tension the back stay. THEN go out in a stiff breeze to be able to get to a 20 degree heel and visually make sure the mast is still plumb and straight and that the leeward cap shroud never goes slack plus some other factors and the mast does not take a negative mast prebend. I now have a Loos gauge and was really surprised at how tight the cap shroud tension was in the spec. However, tensioning by feel (maybe I don't have a good feel :wink3:) my leeward shrouds where flopping in the wind when close hauled in a stiff breeze.
 
Last edited:
Oct 19, 2017
6,875
O'Day 19 Littleton, NH
They shouldn't be flopping, but just shy of loose is what I go for on a beam reach in 15 to 20 knots wind.

-Will (Dragonfly)
 
Oct 26, 2010
1,405
Hunter 40.5 Beaufort, SC
Will, agree. When looking at the Selden Tuning guide I note that my rig (Fractional, two sweptback spreaders, and a backstay) is one of the most difficult to tune and keep in tune and requires more tension in the cap shrouds than most rigs. From looking at the other types of rigs, the tension is more on the order of 15%. The difference in the hand "feel" of the tension from 15% to 20% is remarkable. That's why I got the Loos gauge. The biggest factor is making sure it starts plumb, straight and with the correct pre-bend and stays that way during sailing conditions and does not invert or generate an "S" curve laterally when under load. I am sure the more you get experienced with your particular rig the easier it is to tune by feel. Kind of like "perfect pitch" with just your ear when tuning a piano.
 
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kbgunn

.
Sep 19, 2017
145
2006 Hunter 38 4410 Lake Lewisville, TX
Hi all,
Thanks for the great replies. I should have been more specific in the original post. I've already performed a lot of the measures described such as centering the mast athwartship and straight sighting up the mast slot. My main concern was that the tension on the port side seemed to need a higher adjustment than the starboard side to keep the lowers from flopping around when close hauled. I understood they needed to be just shy of floppy. So on the starboard side that was at 16% of BS. On the port it is more like 18%. So the question is really: is there some other aspect of the rig I have overlooked or is this much variance between port/stbd normal?

My only other experience is with a Cat 22 which was close to the same tension on port/stdb.
 

JRacer

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Aug 9, 2011
1,233
Beneteau 310 Cheney KS (Wichita)
I would double check to be sure that mast is in column and centered. Implication from the tension difference P/S is that the top of that stick is not in column with the bottom and/or it is leaning to one side. Are all the shrouds of the same vintage? Thinking that one side is perhaps stretched more than the other. Presume you are measuring with the Loos with the backstay loose.
 
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Likes: Will Gilmore
Oct 26, 2010
1,405
Hunter 40.5 Beaufort, SC
So on the starboard side that was at 16% of BS. On the port it is more like 18%. So the question is really: is there some other aspect of the rig I have overlooked or is this much variance between port/stbd normal?

My only other experience is with a Cat 22 which was close to the same tension on port/stdb.
My main concern was that the tension on the port side seemed to need a higher adjustment than the starboard side to keep the lowers from flopping around when close hauled. I understood they needed to be just shy of floppy. So on the starboard side that was at 16% of BS. On the port it is more like 18%. So the question is really: is there some other aspect of the rig I have overlooked or is this much variance between port/stbd normal?.
I'm not so sure that the difference is significant between 15% and 18%. The Loos gauge is merely a spring and two "pins" that stress the wire when the spring is pulled and hooked on the shroud. I'm not even sure that if you put it on, take it off, and then put it on in a slightly different height you might get 1% or so difference. The guage isn't that precise. I would also guess that if you delve deeply into the "specs" for a Loos gauge I'd be surprised they will state that the gauge isn't + or - 2%. Maybe less but I'd be highly surprised. Make sure you are taking the readings at the same height on the shroud and try putting it on and then take a reading, take it off and do it again and see if the readings are exactly the same. Just asking.
 
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Likes: justsomeguy
Oct 19, 2017
6,875
O'Day 19 Littleton, NH
The tensions should (will) match on one side or the other. To tighten the starboard side is to tighten the port side at the same time. Pull on the starboard cable and it puts tension across the system to the port side. They should equal out. The only explanation for a turnbuckle that goes loose on one tack while its opposite doesn't go slack under the same but opposite load while of equal lengths are differences in the stretch between cables. This could be the lower or the upper stays. It could also be affected by having your spreaders attached at different angles, such that they are pushed against the mast with different force from one tack to the other. You may be getting a bend from the port spreader that you are not getting from the starboard spreader.

-Will (Dragonfly)