plenamar

Slack leeward shrouds

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Leeward shrouds on my 30 ft half-tonner show substantial "slackness" when sailing upwind in a 15-18 (apparent) windspeed. Is this normal? Shoud shrouds be adjusted tighter? 

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Depends, the book says they should be tight. OTOH, mine are so slack that they need a bungee cord to the lowers to stop them banging around, at least .5m movement. The rationale is to allow the top to fall off in the puffs like a dinghy. 

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General rules: mast must be in column at the dock, tension uppers first, then lowers, shroud tension no more than 15% of wire breaking stress, leeward shrouds should be just tight.

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comparing to a racing tune,  upwind in 15-18 you would want just slight looseness,  say 1-2" deflection, on the leeward cap shrouds.

 tune the lowers to straighten the mast.

 We would only want to see large deflection in the leeward caps in <7kts and slop...

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18 hours ago, Gutterblack said:

Depends, the book says they should be tight. OTOH, mine are so slack that they need a bungee cord to the lowers to stop them banging around, at least .5m movement. The rationale is to allow the top to fall off in the puffs like a dinghy. 

0.5 mt movement? That is 50 cms? 

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On 6/11/2018 at 7:49 AM, Feisty! said:

Why uppers first ?

I  believe it is ensure that the mast is centered port-to-starboard. 

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2 hours ago, Bull City said:

I  believe it is ensure that the mast is centered port-to-starboard. 

I keep hearing that, but it assumes that the spreaders are centered to start with or that the mast is straight when no tension on shrouds.

If subsequent tweaking of lowers moves spreaders laterally, the masthead will go with it.

I center the hounds with the lowers then straighten the mast with the uppers ...

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Because it's the uppers that hold up the main part of the mast, the lowers are mainly there to keep the spreaders from moving around. This is considering full sail, reefed the situation can change.

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59 minutes ago, Feisty! said:

I keep hearing that, but it assumes that the spreaders are centered to start with or that the mast is straight when no tension on shrouds. The spreaders should be such that the angle made by the upper shroud and the spreader is the same above and below the spreader. This is usually not a problem if the spreader mounting bracket is correctly done.

If subsequent tweaking of lowers moves spreaders laterally, the masthead will go with it. Hmmm... I don't follow this.

I center the hounds with the lowers then straighten the mast with the uppers ... This is the reverse of what I have read in tuning guides and what I picked up on SA forum recently, and from the Loos Gauge guide.

You can check whether the mast is centered by using the main halyard, provided it's not too stretchy in which case haul a metal tape to the top, to measure to the port & starboard chain plates. Use the uppers to get it centered, and then tension to the proper % of breaking strength or Loos Gauge setting. Then sight up the mast groove, and use the lowers to address any bend, and then tension them to the proper % of breaking strength. 

I think the problem with loose leeward shrouds is the possible shock load on the hounds when you tack.

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The upper shrouds, from the spreaders up, form a triangle, which is geometrically rigid; from the spreaders down, they form a rectangle, which is not.

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22 hours ago, Bull City said:

You can check whether the mast is centered by using the main halyard, provided it's not too stretchy in which case haul a metal tape to the top, to measure to the port & starboard chain plates. Use the uppers to get it centered, and then tension to the proper % of breaking strength or Loos Gauge setting. Then sight up the mast groove, and use the lowers to address any bend, and then tension them to the proper % of breaking strength. 

I think the problem with loose leeward shrouds is the possible shock load on the hounds when you tack.

don't forget to take the boom off...

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22 hours ago, Bull City said:

You can check whether the mast is centered by using the main halyard, provided it's not too stretchy

I do it with a fish scale on the end of the main halyard taken down to the chainplates. Adjust until scale reads the same on both sides.

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3 minutes ago, fucket said:

I do it with a fish scale on the end of the main halyard taken down to the chainplates. Adjust until scale reads the same on both sides.

Very ingenious.

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5 hours ago, fucket said:

I do it with a fish scale on the end of the main halyard taken down to the chainplates. Adjust until scale reads the same on both sides.

I put a weight on the end of the halyard, as even with a dyneema halyard how hard I pull on it clearly makes a difference a the low level of tension I can put on it by hand whilst trying to measure.  But the scale is even better.

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51 minutes ago, xyzzy said:

 

I put a weight on the end of the halyard, as even with a dyneema halyard how hard I pull on it clearly makes a difference a the low level of tension I can put on it by hand whilst trying to measure.  But the scale is even better.

Yeah, it's awesome. I stole the idea from my sailmaker.

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An inch at the chainplates is a foot at the masthead. And then you are relying on those loose boatyard tolerances for chainplates, decks and hulls. Knock yourself out, but consider squaring the mast with the shear, floors or keel if you think precise masthead position matters.

I gave up with precision when I noticed I could see the backstay with my eye at the forestay...

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Before the "race" last night, we "snugged up"  the rig.....

We "snugged" to the point of having forward  mast bend.....

We promptly reversed our experiment in sailboat physics....

And the race was abandoned for lack of wind..

Nevermind, carry on............

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As rushman says, slack caps on a mh rig are fine. My old boat probably had even slacker caps than his. Used to open the slot on a narrow boat with a lot of shape in the main. Flopped around for nearly 50 years with no dramas. Stewart 34 if you all didn't guess. 

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On 6/13/2018 at 2:08 PM, fucket said:

I do it with a fish scale on the end of the main halyard taken down to the chainplates. Adjust until scale reads the same on both sides.

but what happens if the tension is the same , but one side is 2" shorter than the other?

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17 hours ago, Grande Mastere Dreade said:

but what happens if the tension is the same , but one side is 2" shorter than the other?

I'm not quite sure what you are asking here. If your uppers have the same tension but one is short, then your mast won't be in the center of the boat.

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On 6/16/2018 at 2:31 PM, fucket said:

I'm not quite sure what you are asking here. If your uppers have the same tension but one is short, then your mast won't be in the center of the boat.

 

ok, i see how you're using the fish scale..  rig tension... . doh..   i though it was being attached to the halyard and used at each chain plate..

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41 minutes ago, Grande Mastere Dreade said:

 

ok, i see how you're using the fish scale..  rig tension... . doh..   i though it was being attached to the halyard and used at each chain plate..

No, you had it right, I'm attaching it to the halyard and taking the scale down to each chain plate. Your question just doesn't make much sense in that context.

I use this scale:

61HzGpFHyUL._SL1300_.jpg

I put the hook on the halyard and take the end of the tube down to the same spot on each side. The length of the halyard is adjusted to get the results to fall on the scale of the scale. If the distance from the halyard sheave to the chainplate is longer on one side, the scale will read a higher number on that side than on the other.

It's the same idea as taking a halyard down to the same spot on both sides but controlling for how much tension is applied to the halyard.

 

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