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Old 12-12-2016, 15:23   #1
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Single braid dyneema sheets?

In the last two years our jib sheets have parted 4 times. They can probably stand to be shortened just one more time. I really ought to replace them -- they have 20k+ nm of use on my watch and an unknown fraction of the PO's 45knm on them too -- so I feel they've had a long life.

The point of failure tends to be where the line passes through the genoa car. I'd prefer to avoid replacing the genoa cars.

Currently we use 16mm doublebraid polyester (I thought it was 18mm, but I measured!). The line is moderately stiff and heavy, and I'd prefer to go to something lighter. If we went to a higher-tech line we might come down a few sizes and still provide the needed strength.

I spoke to my sailmaker (Mack), and they suggested sticking with polyester as, ultimately something needs to stretch, and they feel it is best that it be the sheets. Virtually all of the higher-tech lines of comparable strength (~20k pounds breaking strength) have much lower stretch, though.

If I do switch to a dyneema cored line, I wonder if I really need the polyester cover. The lines are always handled on winches.

And so my questions are these, do other cruisers use high-tech lines for jib sheets? Do you like them? Do you use single-braid lines (Amsteel, Endura-12, etc.) as jib sheets without polyester covers? What are your experiences?

I'm thinking that an Endura-12 type line would have a smaller diameter (11-12mm) thus making the ratio of line diameter to sheave diameter more favorable. Also, the light weight of the line, while probably negligible from a performance perspective, may be easier to handle. There are no clutches on the sheets (as on halyards and downhauls/furling lines) and so I have more flexibility with line size.

BTW, the genoa is about 1100sf. At 30knts apparent, calculators tell me to expect about 4200# sheet load. With a factor of 5:1, that puts the target breaking strength at around 21k#.

I appreciate being able to benefit from your experiences here.
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Old 12-12-2016, 15:42   #2
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Re: single braid dyneema sheets?

Hello,

We use entirely high-tech lines on our boat, all of them with aramid cores and polyester covers.

I do not think that stretch is really desirable in control lines. Racers certainly spend a lot of money trying to avoid it.

I don't think that you will be very happy with a line like amsteel 12 or similar. For one, I think that you will find it to be far too slippery for the winch to perform well. Second, you lose the chafe resistance of the cover, and finally, aramids aren't generally as good at UV resistance.

So, yes, I would say that you're on the right track- low stretch and more strength is a good thing. And, even with a braided line, you'll get away with a smaller diameter than 16mm.

Good sailing, TJ
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Old 12-12-2016, 16:05   #3
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Re: single braid dyneema sheets?

I love Dyneema! My boat had 5/8" sta set sheets; I switched to 7/16" Warpspeed and love it. Definitely you want the cover in the area where you handle the line and it's on winches or clutches. I'd recommend just going with Warpspeed or Endurabraid. It's great to down size the line and have more strength. Make sure the smaller diameter line will work in your winches!
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Old 12-12-2016, 16:47   #4
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Re: single braid dyneema sheets?

I've replaced many a sheet. As was pointed out by an earlier poster, if you have self tailing winches they limit the range of diameters you can work with.
Start there.
Then see what the available lines, high and low tech are that fit. Last time for me I needed 12mm and ended up with a blended core double braid. poly/dynema core, poly cover. I don't know if anyone makes that in 16 or 18mm, but maybe.
I would like to replace my current too stiff 18mm lines (new boat) so I am curious.
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Old 12-12-2016, 17:12   #5
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Re: single braid dyneema sheets?

I have to disagree with the advice from Mack. Usually in my experience the chaff in the
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Old 12-12-2016, 17:16   #6
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Re: single braid dyneema sheets?

Not sure why things froze in the middle of my post. Wear in sheets at the deck block is usually caused by stretch. Eliminate some of the stretch and you'll be happy.
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Old 12-12-2016, 17:54   #7
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Re: single braid dyneema sheets?

With sheets this size you absolutly need to step up to a dyneema core line. But the major limiting factor is likely going to be the minimum size your winches can handle. A step up to just covered dyneema is likely to reduce the line size to the minimum the winches can handle, but if you have some room for even smaller line then I would also look at a higher grade of dyneema than sk-75.

The cost per lb of breaking strength gets a little funky, but in high load lines it often works out to be cheaper to step up in grade, down in size, and remain about the same in MBL. You really just have to play with it a bit. Prices change regularly and sometimes you can get a deal. Particularly if you are buying a half spool (300') or more and can fine a rigger with some lying around.

As for uncovered dyneema... no, you can't do it. On a race boat you might be able to get away with stripping the cover some places (or adding cover just where you need it) but it results in a very technical rope for a cruiser that can't easily be used for anything else.

Now whichever line... Warpspeed (Samson) or endurabraid (NER) (sk-75 core, polyester cover) are good go tos, but every quality rope manufacturer makes a line in this class now.

FWIW 16mm doublebraid polyester has a MBL of about 14,000lbs. So you are pretty far below your desired strength. You have to go up to 20mm to approach 20,000lbs. By comparison 12mm endurabraid has a MBL of 21,000lbs. Or you could step down to 11mm and stay the same strength of 14,500lbs as the polyester you are using.


One further note, make sure the sheaves on the sail track spin freely. You still need to replace the line, but if the blocks are frozen it can accelerate the problem.
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Old 12-12-2016, 23:31   #8
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Re: single braid dyneema sheets?

A biggie wear accelerator in Dyneema in such applications has to do with the sheave radius. As the part of the sheet that's right up against the sheave has a "shorter distance to travel" than do the fibers at the same point in the line, on the outside of the radius at the sheave. Since the outside fibers are transcribing a larger arc (more distance travelled) than those nearer to the sheave's surface, & thus they get more heavily tensioned than those right on the sheave. Which of course makes them have to take more than their fair share of the load. Ergo, accelerated aging of the line in that section of it, & in any others where similar unequal fiber loadings take place. Which is also why larger diameter sheaves or bends in the line are better.

One other thought is that you probably don't want to go much smaller in overall diameter than 1/2". As there are obviously times when you'll be applying a good bit of load to the lines by hand, which is difficult with thinner lines. And also, when going forward, the jib sheets tend to be natural handholds (even if it's not the most seamanly practice). So that it's good to have lines that are thick enough for everyone to be able to easily grip them. Particularly if that's the only thing within reach if they lose their footing for whatever reason. Or get bowling-pinned by a wave, especially when working to leeward.


Edit: I'd concur with the idea of buying line for a boat of size by the spool. It works out better fiscally. And I've yet to sail on any boat of 10m or more that didn't have use for a spare sheet, or a spare set of sheets. Having such is simply in league with doing things like keeping a dry change of clothes onboard. A common sense thing.
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Old 13-12-2016, 04:35   #9
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single braid dyneema sheets?

With all respects to the previous posters, I disagree. Your sailmakers advice is golden and is probably based on experience with the downside of no stretch control lines on older boats.

Assuming this is going on your older boat, you are moving the structural failure point from the sheets to elsewhere. The stretch in the sheets means that in a gust the sails are not stretched, there is a smaller load increase on the windward shrouds, chain plates, etcetera. If you doubt the feasibility of this, on another "more rambunctious" forum there were some pictures of 1-2 failures of this type. Can your boat's mast and standing rigging take the added load? Hard to say without inspection.

On my boat, the newest generation of lines is only used for halyards.

Finally, if the sheet is wearing where it goes through the car, a careful inspection of the cars would be best practices. Do they still turn smoothly? Are they "sloppy"? Given the cost of sheets on a boat your size- Wouldn't it be prudent to rebuild or replace them?
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Old 13-12-2016, 05:02   #10
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Re: single braid dyneema sheets?

Switching to Dyneema doesn't solve your problem. if your sheets keep parting at the cars, then you likely have a chafe issue at the cars. All switching to Dyneema will do is make the chafe more expensive. fix the chafe problem first. doesn't have to be an expensive fix, just potentially needs a file and some wet dry sandpaper. it could be as simple as a bur on the edge of a car body.

You didn't mention if this is happening on both sides or just one side.
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Old 13-12-2016, 06:07   #11
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Re: Single braid dyneema sheets?

Gent's this topic is one of those where you really need some live experience on big boats in weather in order to see what happens. I've seen more massively over-spec'd sheets part in the vicinity of genoa cars than I can count. Sheets made from most rigging materials, including wire, & high modulus line. It's a matter of the loads, as well as how the geometry of the lead angles magnifying them that kills sheets. Even wire ones on free rolling cars.

The new guy, Mischief_Inc explained it to a decent degree. How & why they wear/fail I mean. Especially since if the cars were truly that bad, sheets would be parting with a fair degree of regularity. And with Dacron sheets, if there were major issues with the cars, it's likely that one would see problems with the sheets during just a routine tour of the deck. Since if the cars are rough, the sheet's covers would be exhibiting obvious signs of chafe.

Ditto to some degree if they have smooth surfaces but they're sticky. That or the lines could even develop some harder spots where the fibers were being heated from the friction from sticky sheaves in the cars/blocks.


As an example of some of this, some of my early racing was on 45'-50' IOR boats in the mid-80's. And we led the running rigging on deck for everything daily. So all of the sheets & guys got a defacto pre-race inspection each day. They were heavy stainless wire spliced to thick dacron tails. And were led over Harken ball bearing jib cars.

It was pretty common to blow one if the wind was up, & invariably they'd fail right at the exit point from the lead cars, or a few inches above it. The thing is, the only warning that they might give prior to breaking was by sound. No chafing, or other obvious signs of wear on them, before or after they died.

Also, when they broke, the break was pretty dang clean. With 90-95% of the strands all breaking within a couple of millimeters of one another. So much so that it looked like a clean cut. Only with the wires all flayed out like someone's hair if they licked a live wire.

So it's not at all necessarily the OP's lead cars which are causing the problem. Though, yes, it would definitely be wise to take them apart & give everything a good servicing prior to taking the boat out saiiing again.
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Old 13-12-2016, 07:17   #12
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Re: Single braid dyneema sheets?

Thank you, everyone. There is no chafe at the cars, but the line does bennd through 30 degrees or so over a radius of a couple inches. With gusts, or as the boat moves through any significant seas, the stretch is visible and the line moves back and forth through the car an inch or so. I have a video of this from a few months ago I'll try to post.

Sheets on both sides have parted (twice, each)

My cockpit winches (the ones that matter for jib sheets) handle lines down to 8mm.

Looking at double braid spectra/dyneema, I believe i would need 12-14mm.

I do have many spare lines on the boat, and when I replace the sheets I intend to keep them as spares. My concern about buying a spool would be that the lines from it would all have the same colors. As I often sail with different/new crew, it is useful to be able to refer to a line by color. For example, without tracing the line back and forth, it is easy to confuse a genoa and staysail sheet.



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Old 13-12-2016, 07:38   #13
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Re: Single braid dyneema sheets?

Here are two videos from last April. Even in those light winds you can see the sheet move back and forth an inch or so at the car.

At one point the camera pans forward and you can see the remnants of the sheet that had just parted hanging from the clew.


One video

Another video
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Old 13-12-2016, 07:59   #14
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Re: Single braid dyneema sheets?

Yes the stretching of the line under load accelerated failure. Every time it stretches it generates heat, that heat over time builds up and in extreme cases can even melt lines. Properly sized sheets should not visibly pump like that, meaning your sheets are understrength, and the wrong material.
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Old 13-12-2016, 08:24   #15
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Re: Single braid dyneema sheets?

Quote:
Originally Posted by Stumble View Post
Yes the stretching of the line under load accelerated failure. Every time it stretches it generates heat, that heat over time builds up and in extreme cases can even melt lines. Properly sized sheets should not visibly pump like that, meaning your sheets are understrength, and the wrong material.
Yep, the above, exactly. Your sheets right now are like rubber bands! And given your displacement, & thus righting moment, stronger, & less stretchy sheets are better. Though even with Dyneema lines, the run is long enough that your sails won't take a beating from them. Since stretch is also proportional to length. So there will be enough stretch in the new sheets due to this.

What size are the sheaves in your jib cars? Perhaps they only seem small since the boat is big, but I'm still curious.

When I mentioned spare sheets, I meant literally that. So that you'll have the proper line around for the job when one or both get worn. Plus there are times when you run 2 sheets to the clew at the same time, on one side. Or need a spare sheet in order to assist with changing sails etc.

Some tips:
- Fix your lifelines.
- Seize the Pelican hooks on them shut at sea. For obvious safety reasons. You can skip it on daysails.
- When tying bowlines onto things, sails especially, don't make the loop through/around whatevers being tied more than a few inches long. As big open loops tend to snag on things, & then when the sail fills with them snagged, something bad is likely to happen.
- Tune the rig. It looks like your leeward shrouds are a touch floppy. And be sure to tape over all of your cotter pins.
If the shrouds are floppy, they'll suffer from some of the same types of wear as shock loaded, or stretching lines. Which is bad for their health.


Edit: Good job on posting the videos. Much appreciated.
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