Hybrid standing rigging

[DumnMad]

Originally Posted by wingssail

Yes, we did

So less than a third the cross section and more elastic. A very unusual move.

[wingssail]

Originally Posted by DumnMad

So less than a third the cross section and more elastic. A very unusual move.

1/3 the cross section? No, I don't think that is the case, 1/4 inch (the steel we replaced) would be 6.35 mm. We replace it with 4mm. It is 63% of the cross section, but cross section size is not the issue.

The real issue is the strength (and the weight, more on that later).

We have found that elasticity is an issue, but not insurmountable.

Strength:
The wire we previously used had a breaking strength of 8200lbs. The dyneema we chose (amsteel blue, 3/16, sold as 4mm) had a breaking strength of 5400lbs. So that is less, obviously. But the calculated max load on our halyards was roughly 3000lbs (in maximum wind strength for the largest sails, with a safety factor).

At any rate we felt it was within safe limits. We could have been wrong.

Weight:
However, weight is also a factor in the decision. We are a racing boat, so we do not wish to carry unnecessary weight aloft. Changing from wire to dyneema for halyards and other running rigging, as well as lifelines, saved us about 150lbs aloft. It was worth it to us to go for the lightest practical line size and increase as needed. We feel that the weight reduction aloft has made us faster, which wss the goal.

We broke some halyards, but it seems that it was a splicing error. Since we corrected that we have not had any further issues (three seasons).

While cruising we do not load the boat to anywhere near the same extant, and we feel safe with the dyneema we have now. (BTW, we increased the mainsail halyard to 8mm, there are no spare mainsail halyards on our boat).

Our decision may be interesting, but it was calculated

[DumnMad]

3/16 may be 4mm after being stretched ?

Cross section is proportional to the square of the diameter. Therefore 0.63 x 0.63 =0.4
Dyneema has some 3 times the stainless elongation at breaking.

Therefore in the order of 3 x 0.4 = 7.5 times more stretch at breaking.
Somewhat less at working loads I guess.

I still think it's a big change in elasticity from stainless.

Now 8mm, that seems a fair exchange.

[RaymondR]

Have to agree on the 8mm.

Not sure I'd even hoist a flag on 4mm.

[GILow]

Originally Posted by merrydolphin

I had a KP 44 for nearly ten years. And tens of thousands of miles. Great boat!



I replace the standing rigging once. Did it myself with traditional SS wire, swagged aloft and Sta-locks on deck.



I would not want to experiment with this. Yes, very tempting but still a think a bit early to get into it for a cruising boat. A hi-tech racer with professional hi-tech maintenance maybe, but not a KP44 with Joe Cruiser.

I say this in the nicest possible way… but WTF is with the ultra conservative KP44 sailors out there?

Seriously, there’s some kind of weird sh-t going on where they all treat the boat as some kind of bl—dy shrine.

THOU SHALT NOT CHANGE AN.YTHING ABOUT A KP44!

I honestly believe Doug Peterson is up there in the good place, sipping a Mai Tai and shaking his head, wondering why nobody is willing to fiddle with his boat. If I was Doug I’d be banging me head on the nearest celestial wall with frustration.

Look, it’s a good boat, ok. But times have moved on and I’d bet Doug would be THRILLED to reduce weight aloft on the rigging.

I’d also bet he’d love to reduce the weight of that horrendous Jack Kelly fitout, all that faux teak, all those monstrous iron tanks. Two outrageously heavy bathrooms, ponderous hot water system, monolithic and over sized engine.

The poor boat was destroyed by mass.

I left the KP44 forum in disgust because they all treat the boat as some kind of sacred cow, utterly unwilling to accept that there are countless new and better ways of doing things.

Synthetic rigging is NOT the bl—dy mark of the devil, it’s a very good way of making an old cruising boat sail better. It is NOT too f—-ing early to get into this stuff for a cruising boat, it’s the right f—-ing time,

Sorry mate, you hit a nerve.

I’m over the weird reluctance to embrace change.

[wingssail]

Originally Posted by DumnMad

3/16 may be 4mm after being stretched ?

Cross section is proportional to the square of the diameter. Therefore 0.63 x 0.63 =0.4
Dyneema has some 3 times the stainless elongation at breaking.

Therefore in the order of 3 x 0.4 = 7.5 times more stretch at breaking.
Somewhat less at working loads I guess.

I still think it's a big change in elasticity from stainless.

Now 8mm, that seems a fair exchange.

To be honest I am not sure I follow the entirety of your calculation.

We have not observed elongation in our headsail halyards (4mm) or reduction of diameter under load but keep in mind that our halyard loads are below 2000lbs (determined at the winch), which is far below the SWL or breaking strength of 4mm Amsteel. Samson, who make Amsteel, claim that elongation is less than .5% at 10% of breaking strength which is closer to the tension we put on our halyards. At any rate elongation (stretch) which we see as slack on the hoist of the sails is easily observable, if present. We tension the halyard until the sail looks right and that includes taking up any stretch, and it stays there. The mainsail is different. For some unknown reason the luff of that sail goes slack by about 4" even after it has been sufficiently tensioned, after a couple of minutes, and that is the one with 8mm on it.

But none of this is germane. We selected 4mm (3/16) based on its strength, not its size under load. We had failures initially (though none after we changed our splicing technique) and for that reason, and the cost of periodic replacement, would not consider it for standing rigging.

Originally Posted by RaymondR

Have to agree on the 8mm.

Not sure I'd even hoist a flag on 4mm.

RaymondR, I am sure that 4mm dyneema is sufficient for many applications on a sailboat the size of yours, and with an approach of over spec'ing things you would make your boat heavier and slower than it needs to be. (thick rope aloft is windage).

[Cheechako]

Originally Posted by GILow

Hi all,

I'm replacing the standing rigging on my Kelly Peterson 44. She is currently rigged with Sta-Lok terminals in a combination of 10mm and 8 mm wires where appropriate.

After a lot of reading on the subject I have lots of ideas, but one idea is a little hard to evaluate.

I would like to reduce weight aloft by using as much synthetic rigging as possible, but I do like the idea of having the lower shrouds made from stainless to deal with my concerns about chafing. Likewise the forestay and staysail stay, as they have furlers.

So this would leave me with synthetic rigging for everything else above the lower spreaders, plus the backstay, plus the fore and aft lower stays.

Has anybody tried a similar approach or are you aware of any pitfalls to this approach?

Matt

I would worry a bit about the difference in stretch/modulus of elasticity with a hybrid mix. You dont want your rig tension going awry under heavy load. Just saying.... you better compare the two for elastic stretch characteristics...

[GILow]

Originally Posted by Cheechako

I would worry a bit about the difference in stretch/modulus of elasticity with a hybrid mix. You dont want your rig tension going awry under heavy load. Just saying.... you better compare the two for elastic stretch characteristics...

There’s plenty of good documentation on the issue. A few of the major riggers publish charts to make it easier.

And there would be no mismatch around the vertical plane, which is where you’d have problems with uneven stretch.

If both upper diagonals stretch at a different rate to the lower verticals it won’t put the mast out of true. It may slightly change the angle of the spreaders, but it would be almost too small a change to measure.

Actually, from a total purist point of view, the fact that the synthetic stuff elongates in the cold is good, as it would offset the very slight contraction of the stainless rigging. And vice versa for hot weather.

[RaymondR]

Not sure about that reasoning GIlow.

My understanding of how things work laterally is that the lowers keep the section between the stepping point and the mast attachment point vertical and then the uppers, and intermediates keep each section above vertical.

If the lowers serve to do so and then the upper sections are supported by stretchier shrouds a bending moment will be generated in the mast at the point of attachment of the lower and/or intermediate attachment points.

The difference in lengths of the shrouds also have to be taken into consideration, since a longer bit of string stretches more than a shorter even though the stretchines is the same.
You could probably compensate by varying the pretensioning but all in all it sounds like a trick business.

[GILow]

Originally Posted by RaymondR

Not sure about that reasoning GIlow.

My understanding of how things work laterally is that the lowers keep the section between the stepping point and the mast attachment point vertical and then the uppers, and intermediates keep each section above vertical.

If the lowers serve to do so and then the upper sections are supported by stretchier shrouds a bending moment will be generated in the mast at the point of attachment of the lower and/or intermediate attachment points.

The difference in lengths of the shrouds also have to be taken into consideration, since a longer bit of string stretches more than a shorter even though the stretchines is the same.
You could probably compensate by varying the pretensioning but all in all it sounds like a trick business.

Well, that got me reaching for a pen and paper…

Ok, my logic was to make all of the lower stuff stainless, and everything above the first set of spreaders synthetic.(Let’s ignore the fore and aft stays for the moment.)

I already have discontinuous rigging, which is not standard for this boat, but the mast is still vertical… so far so good.

So, for the bit up to the first spreaders, I can’t see any difficulties. The stainless is pretty darn stable stuff and we all know it well by now.

Now, let’s assume for a moment my navigation skills are even worse than I suspect, I miss Tassie altogether on my next jaunt and find myself down in Antartica wondering why all the locals look like penguins.

In this case, everything above the first set of spreaders is now a little loose. Everything. So there’s no imbalance of forces. The lower spreaders are now drooping slightly because the stainless lower section has not lengthened the way the upper section of rigging has, but we are talking an absolutely tiny amount.

As for the fore and aft stays, this is where I do have a dilemma.

I am going to stay stainless on both the forestay and the staysail stay, as those have furlers.

I would have liked to go synthetic for the aft stay but I AM a little worried about the different rates of stretch maybe causing problems, plus I’m uncertain about chafe on the aft stay, so on balance I suspect I will stick to stainless there too.