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post #11 of 42 Old 07-28-2015
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Re: Rig tension too tight?

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Originally Posted by Holland View Post
I don't know the facts and figures of rigging but my boat is an old CSY cruiser and the problem i've had with riggers is not having them pull it down hard enough. without the option of readily adjusting the rig at sea i have been hove to protecting my sails with a trisail hoisted and watching the forestay flogging with a furled headsail. much prefer a constant pressure.
not sure what constant pressure means.
if the forestay is to loose then you need more back stay tension . you adjust the length of the forestay for mast rake and then adjust the forestay tension by tightening the backstay

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post #12 of 42 Old 07-28-2015
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Re: Rig tension too tight?

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Originally Posted by overbored View Post
the 15% is a starting point. the rig will require tuning after you sail the boat and determine the mast bend and how the mast is in column. the shrouds should be adjusted to give the mast the correct shape required by the rig designer and this may require that some sets of wires are at very different % settings when static. you can not just set them to 15% and say thats good, you need to sail the boat and check. the riggers know how the set up certain types of boats so the owners do not have to do as much adjusting after the initial set up.
The loads on the rigging while sailing are way more then the static loads when you are at the dock. most production rigging is set to be 50 to 60 % load during a knock down. the wire does stretch at these loads but does not permanently yield until just before it breaks.
rigging steps would be to:
set up at 15% making sure the mast is straight in column
go sailing in the average breeze for your area
check mast for bend and shape in column
makes notes of needed adjustments
adjust rigging at the dock
sail again and check mast and sail shape
after you are happy with the mast shape check with loos gauge and record the numbers for future reference.
adjust mast rake to set amount of weather helm
with straight spreaders the shroud tension should not change much but could effect the lower shrouds
with swept spreaders every thing could change so check mast shape and shroud tension for new reference numbers
15% is normal, especially for the forestay/backstay ... as the sailmaker depends on the amount of predictable sag in the forestay wire when designing the luff shape of your wind loaded genoa/jib at near it's designed maximum wind range.
What you dont want to have is when the boat is heeled over at a ~45 angle is that the rigging exceeds ~30%, or when sailing that the forestay/backstay exceeds 30% ... which is / can be the 'yield' for some of the rigging components
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post #13 of 42 Old 07-28-2015
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Re: Rig tension too tight?

This is a good source for rigging information (go to page 28 and keep reading):

http://www.riggingandsails.com/pdf/selden-tuning.pdf

Note: that selden sometimes recommends going to 40% of breaking strength of the wire, which in my opinion is too high, and as RichH posted above, anything above 30% can yield a stainless part or wire. There fore I would keep loads at 15% or below.

Here is specs for 304 ss. Note that even if the stainless is 304, it can vary in strength as far as breaking and yield. Basically once a material has yielded, it should be considered as failed, as it has stretched and will not return to same dimensions. When that happens, the area of the part restraining the force has gotten smaller, and thus the associated stress lbs/in2 has gone up for the same loads- this leads to higher stresses on the part for equivalent loads. Here are stainless specs:

ASM Material Data Sheet

Yield over break strength = 31.2 ksi/73.2 ksi =42.6 %

So if you hit 43% of breaking strength on a 304 ss wire, the wire will yield and should be considered failed (now the cross section dimension of the wired is smaller than as new and will not return to its original dimension. More loads to 43% will rapidly breaking the wire, especially considering the rig wire will start to go slack (even at the dock) and the associated shock loading will eventually break the rig. Now if you keep rig loads down to 20% of breaking wire strength, even fatigue failure will be significantly reduced, and 15-20% load should be more than enough to keep your rig "tight" which will reduce shock loads.

Here are Loos instructions for tuning (recommending 15% as a max forestay tension):
http://loosnaples.com/how-to-use-pt-...tension-gauges

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Last edited by casey1999; 07-28-2015 at 06:14 PM.
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post #14 of 42 Old 08-03-2015 Thread Starter
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Re: Rig tension too tight?

Emailed the rigger with the backstay tension. Here is his response:

"We were trying to get head stay tension within the realm of reasonable. If you want to ease off the back stay turnbuckle, feel free to do so but keep an eye on your head stay tension. It is direct correlation."

Seems like he should have made the headstay (roller furler) shorter doesn't it?

I haven't adjusted the backstay yet, but hope my options are not between excessive backstay tension or a floppy headstay!
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Re: Rig tension too tight?

head stay is adjusted to length not tension this sets the amount a mast rake to control the amount of weather helm. the back stay is adjusted to set the headstay tension which controls the amount of headstay sag. head stay sag needs to match the amount designed into the headsail.
Sail the boat first and see how it sails it does seem the rigger knows what he is doing.

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Last edited by overbored; 08-03-2015 at 01:07 PM.
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post #16 of 42 Old 08-03-2015
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Re: Rig tension too tight?

I have a slightly off course question: I have a B&R rig with a backstay (84 Hunter 31). Are the diamond stays tensioned to 15% as seems to be the standard for rigging wire or do they differ due to their kind of unique situation?

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Re: Rig tension too tight?

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Originally Posted by SloopJonB View Post
I have a slightly off course question: I have a B&R rig with a backstay (84 Hunter 31). Are the diamond stays tensioned to 15% as seems to be the standard for rigging wire or do they differ due to their kind of unique situation?
diamond stays are set to length. When the rest of the rigging is set they will have a tension but are set to control the amount the mast bend in the section where the spreaders are located on the mast. you should measure the mast bend of that section while sailing

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Re: Rig tension too tight?

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Originally Posted by SloopJonB View Post
I have a slightly off course question: I have a B&R rig with a backstay (84 Hunter 31). Are the diamond stays tensioned to 15% as seems to be the standard for rigging wire or do they differ due to their kind of unique situation?
I think this is the tuning manual for your rig (takes a while to down load- give it time):

http://www.marlow-hunter.com/export/...US%20Spars.pdf

Looks like tension is 6% of breaking- but read through the manual as I just skimmed it.
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Re: Rig tension too tight?

Cheers - that's just what I needed. I have an Isomat spar with a link plate split backstay so I suspect that info may be for the new model 31. Even if so the tensions are so close to what I figured that I can't see there being enough difference to matter.

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Re: Rig tension too tight?

The point i was trying to make is if you have a rigger check the rig prior to a long voyage and your rig is not readily adjusted at sea then the rig should be set for the worst weather you may encounter, unless you are ready to go on the poop deck with spanner and screwdriver in a strong gale.
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