How much to tension the lower shrouds?

[Neptune's Gear]

Oh yeah, when you are done, a Loos gauge is great for measuring and recording the settings for your boat, so next time you don't have to go through this all again!

[daletournier]

Originally Posted by Revelations

Talking about bending the boat, this was the main reason why we build the boat with epoxy, S Glass/Carbon cloth and Balsa. She is stiff - damn stiff! There is no wear on the step or mast butt - at least nothing yet. However, the lower shrouds are much loser than prior to her cross Atlantic voyage voyage.

Getting a qualified person - this type of work seems to be a bit of voodoo science mixed with experience and gut feel. This is what concerns me more than anything else.

The "voodoo science, gut feel" comment is right on the money in m opinion , that was my take away from doing my own rigging.

[UNCIVILIZED]

Originally Posted by Revelations

Talking about bending the boat, this was the main reason why we build the boat with epoxy, S Glass/Carbon cloth and Balsa. She is stiff - damn stiff! There is no wear on the step or mast butt - at least nothing yet. However, the lower shrouds are much loser than prior to her cross Atlantic voyage voyage.

Getting a qualified person - this type of work seems to be a bit of voodoo science mixed with experience and gut feel. This is what concerns me more than anything else.

Given that it's easy to see the mast base visibly moving, coupled with the fact that your lowers are noticably looser than they were recently, then you need to get the rig sorted out sooner rather than later. Since either some of your rigging has stretched quite a bit, perhaps more than is normal or safe. Or the mast step/the structure supporting it may have been compressed, thus resulting in the loose wires & slop at the mast butt.

Also, I can't see how there wouldn't be some wear in the step & mast butt, since typically, mast steps are designed to prevent any movement of the mast's butt. Plus, with downward loadings on the spar from the rigging probably tallying up to more than the boat's weight, there's going to be some wear in that area if there's movement.
Best to sort it out ASAP.

On the tuning thing, & riggers not measuring tension. Most of us know how much torque to apply to a nut or bolt based on it's size, without needing to use a torque wrench. So my thought is that a rigger, who tune's rigs almost daily, will develop much the same feel for tensioning different size wires by feel, or sound. Yes, measuring things surely can't hurt, & it' something I aim for. But when I asked the team rigger how he tensioned the shrouds on the IACC boat. He told me that it was primarily by sound, as in similar to a musician tuning their instrument. And I believed him. Especially given what was at stake.

[Neptune's Gear]

Yep, that's old school. Pretty much all load cell data with modern race teams...

[svrevelations]

Originally Posted by 44'cruisingcat

......... If the front of the mast is moving, but not the back, it would suggest to me that the mast may be raked aft too far, and isn't sitting flat in the mast step. How's the forestay tension?

You are right. The mast is not sitting flat on the mast step. I took pictures and measurements of this and emailed it to Sparcraft. They replied that it is right and nothing wrong. So is it right or not??? (If not, who the hell can one trust?)

I am unable to measure the upper shrouds tension - but it certainly feels like serious tension. Therefore the fore stay is also under serious tension.

[svrevelations]

Originally Posted by Neptune's Gear

IMO any rigger that does not actually measure the rig tension should be avoided! Otherwise it's a guess. Guessing on expensive structures is not professional. There is a great book available for this - Ivan Dedekam's Sail and rig tuning. If the rig is non rotating, like this one, and a cruising boat, here are some basics, if there is no tuning guide for the model concerned.
Forestay length sets mast rake. Start with 3 degrees. Now, with all shrouds hand tight on clean threads: Make sure mast is vertical - measure Masthead to chainplates on each side. Do it again to the toe rails - is the boat symmetrical?
Now, 15% of break load for the wire. Measure the elongation over a 2m length, elongation reflects load, and can be found online, from the wire manufacturer, or in Ivar's book. Use a steel tape measure, 2m above the swage on each cap. Then, tighten each one evenly till the desired elongation is reached. Check the mast bend - on this rig induced by spreader angle. It should never exceed 1.5 x D ( mast dia, or depth fore/aft). Sight up the sail track on the mast - if it's not in column, it's quite easy to see looking up the track. Tighten the lowers to 10%, ensuring the mast stays in column. Now go for a sail. With the boat fully powered up, the mast should remain in column. Adjust lowers to keep it there, remember same number of turns each side! It's ok if the leeward cap shroud is unloaded when fully powered, just before you'd have to reef, but it should never be loose and flopping around. Loose shrouds can shock load, with dire consequences!
Finally, some mast twist is normal - high end sailing instruments have compensation for this.
There is a great bit in the back of Ivar's book about preload on the rig, and why it actually reduces rig load when sailing. Unloaded rigging just means you have used up the preload.
A proviso here - it can also mean the mast step structure and attachment is flexing - not unusual in a multi.
All just my opinion and experience. Use this info at your own risk. :-)

Thanks Matt!
A lot of info to work through here - but certainly sounds a lot better than this voodoo gut feel thing.

[44'cruisingcat]

Originally Posted by Revelations

You are right. The mast is not sitting flat on the mast step. I took pictures and measurements of this and emailed it to Sparcraft. They replied that it is right and nothing wrong. So is it right or not??? (If not, who the hell can one trust?)

I am unable to measure the upper shrouds tension - but it certainly feels like serious tension. Therefore the fore stay is also under serious tension.

Well, being a DIYer, (I built our boat and built and fitted the rig to it) I'd be inclined to loosen the upper shrouds a little (a turn or two) and tighten the forestay, moving the masthead forward.

This would improve the seating on the mast step, and tighten the lowers at the same time.

But I fully understand if you'd prefer to leave that kind of thing to professional riggers.

[44'cruisingcat]

While they may feel loose, if the middle of the mast isn't pumping at any time, the lowers are as tight as they need to be.

[Neptune's Gear]

No way it's right that most of the load is on the mast heel! This will point load the mast base, and could easily lead to the loss of the rig. If your not confident to fix it, then get a rigger who is happy for you to watch and learn. Until then slacken the caps, and lowers if required to get the mast to sit properly on the step, and don't go sailing!

[UNCIVILIZED]

Originally Posted by Revelations

You are right. The mast is not sitting flat on the mast step. I took pictures and measurements of this and emailed it to Sparcraft. They replied that it is right and nothing wrong. So is it right or not??? (If not, who the hell can one trust?)

I am unable to measure the upper shrouds tension - but it certainly feels like serious tension. Therefore the fore stay is also under serious tension.

Think about what happens when you press down on just one edge of a beer can with a lot of force. The wall buckles & it collapses, right?
A mast isn't all that different, it's base needs to be in contact with the step for a full 360 deg. in order to properly distribute the loads. Especially when you consider that each shroud & stay is pressing it downwards with several tons of force.

Pass on sailing until you both have the boat undergo a structural survey, especially all of the components which combine to support the step. And that you have the rig properly evaluated & rebuilt.

Also, while it's painful to contemplate, you need to start vetting riggers in preperation for the overhaul. Local & possibly otherwise. As with these kinds of problems, plus 7yrs of sailing under her keel, the rig really should have most of her components evaluated.


EDIT: FWIW you can build a DIY "Loos gauge", although it won't give you numbers figures for the shroud tension. But you most certainly can put a scale with hash marks where the pointer is, so that you can compare & repeat shroud tensions.
A Loos Gauge is just a calibrated tool for measuring deflection, & converting that deflection into wire tension measurements.

[svrevelations]

Gentlemen, thank you all for your help, advice and suggestions!
I now have a much better understanding of the issues.

[44'cruisingcat]

JMHO, but when considering having a "professional" rigger look at it, remember the advice you recently received from some "professionals".

I'd feel more confident fixing it myself.

[svrevelations]

Originally Posted by 44'cruisingcat

JMHO, but when considering having a "professional" rigger look at it, remember the advice you recently received from some "professionals".

I'd feel more confident fixing it myself.

Quite! Trust is becoming an issue.

[daletournier]

Originally Posted by 44'cruisingcat

JMHO, but when considering having a "professional" rigger look at it, remember the advice you recently received from some "professionals".

I'd feel more confident fixing it myself.

I lean this way more and more. Often its easier to believe a "professional", im more skeptical than I used to be due to experience. Know one cares like you do. Can be hard to distinguish between the good professionals and the not so good.

[rognvald]

Revelations,
There is no black magic in tuning a sailboat rig as there is not black magic in tuning a violin, cello or classical guitar. However, since your rig will not have a starting point: A 440 Hz like a string instrument, you must find a baseline in order to arrive at your goal. There has been some good advice so far but the basics are: a mast in straight column with no athwartship deviation, fore/aft perpendicularity with a designed mast bend at the top and reasonable tension on your lowers to keep the mast in column. Now, you must take your boat for a sail and observe the mast under the different points of sail being careful to note any deviances or excessive flutter in the rigging. After establishing your initial baseline, take the boat out again and tweak any inconsistencies on each point of sail until a general stability function is established. Now record these parameters with a tension gauge and continue tweaking your rigging--especially in higher wind conditions. After a week or so, you should have a good baseline to record and repeat in the future. This will be a reliable and efficient way to establish your tune but you will find that as you become more involved in the process, you will continue to improve your rig's overall posture until you arrive at YOUR boat's ultimate sweet spot. Don't be afraid to experiment. It's not rocket science and it's your boat. Hope this helps. Good luck and safe sailing.