Dyneema String Theory

[Matthew P]

I recently decided to replace the halyards on Gladys (BR20 GRP, 2009) but before spending £70 or so I asked Jimmy Green for some information which may be of interest and perhaps save JG being bothered by similar inept questions in future.  At the risk of seeming like an advertorial (it isn't), and with JG's permission, the following is my emailed list of questions and JG's patient responses:

MP Question a):
I am looking to replace the 8mm polyster gaff and jib halyards, which are now worn and I suspect also can stretch.  Down-sizing to 6mm would allow me to re-arrange the attachment to the gaff spar and also allow me to use a fiddle block for the head of the jib, which has a restricted mount of room for a long block.  Compared to 8mm Polyester braid will 6mm Marlow Excel Racing be suitable replacement or are there more effective alternatives?

My concerns are:
- I understand the 6mm Excel Racing breaking is 2056Kg compared to the existing 8 mm Marlowbraid (I think) 1740Kg.
- Is 6mm Excel Racing breaking is 2056Kg strong enough in working conditions(ie when knotted, cleated, wet etc) ?

JG Response a) :
"Both lines will suffer a loss of breaking strain when knotted. The racing should perform a little better. Cleating will also be unaffected unless you have clutches. In which case I would need to know which one. Wet or dry makes no difference to either rope."

MP Question b):
The masthead has a 50mm dia "dumb  sheave" (rounded hole) for the gaff halyard and 50mm blocks for the jib halyard.  The existing 8mm polyster braid does not a lot of wear.
- will 6mm Excel Racing wear quickly?

JG Response b):
It has a 1:1 polyester jacket that wears fine. As a smaller line the load will bear heavier on relatively less material. However, it will stretch less and so move less as loads change. You can also put a sacrificial tape around it to protect that particular area.

MP Question c):
I intend to attach the gaff halyard to the gaff spar by threading the halyard through a 6mm dia reinforced hole through the spar and then secured with a figure-8 stop knot.  This knot needs to be secure and yet possible to undo so that the halyard can be moved when reefing, to another hole further up the spar.   
- Will a figure-8 stopper knot, against the hole exit, slip?
- Will it tighten too much to undo? 
- What alternative method is there to a stop knot?

JG Response c):
Under high load a figure 8 knot will become tight. You will either need to tie it with a slip element (ie leave a loop and tail available to pull) or you could look at Clamcleats and add a figure 8 knot as a back-up.

MP Question d):
d) Both jib and halyard are secured to stainless steel cleats with approx 10mm dia throats and 70mm long
- will these cleats be effective for  6mm Marlow Excel Racing with normal figure eight and locking turns?

JG Response d):
Should be absolutely fine. You may want a couple extra turns but all ok.

MP Question e):
The jib halyard passes through a nylon friction cleat on its way into the steel cleat (see d) above).
- Will 6mm Excel Racing resist excessive wear in a nylon friction cleat?

JG Response f):
Again it should perform just fine. All ropes do wear eventually though.
 
MP Question g):
What is the minimum diameter block roller-sheave for 6mm Excel Racing?

JG Response g):
I would keep an eye out for the maximum line diameter specified on the block and stick with blocks that state a 10mm max line. That will keep breaking loads compatible. The Barton size 3 is good. Plain bearings are also better with high static loads. Ball bearings will deform over time and stop running properly, they are better for dynamic loads like sheets.

Following JG's reassuring responses I have fitted the new 6mm Dyneema halyards but have not tried them sailing yet.  I was concerned that the 6mm would feel uncomfortable to handle compared to 8mm polyester but  dry, and on land, they seem OK.

I hope this of interest.

Matthew
Gladys BR20

PS, With some trepidation I have converted my top-mast halyard main attachment to a through-hole, as described elsewhere in this forum.  But I have nervously beefed the area up around the hole with a 200mm long sleeve cut from the base of an old windsurfer mast wrapped around with carbon fibre tape and also inserted a 6mm ID aluminium tube for the rope to run through the mast so that it takes the crushing forces off the mast tube.  For the upper reefing attachment points I am using soft shackle loops to hold the halyard against the topmast in the reefed positions.  If you see Gladys limping along with a bust topmast you'll know why.

[Graham W]

Using thin Dyneema on the halyards is excellent. It reduces windage and weight aloft but there is one important disadvantage - it is really hard on the hands when trying to get some decent tension on it.

This has already been mentioned before but to get around this problem, I strongly recommend one of these http://www.diy-wood-boat.com/Handy-Billy.html, used in conjunction with one of these http://www.kmnautisme.com/shop/en/karver-shop/2357-handle-kjh-karver.html  Incidentally, the second link is to a Breton store because they are significantly cheaper and just as efficient delivery-wise as a UK one. They are in the Gulf of Morbihan. 

If you don't want to splash out on a Karver KJH, you could use one of these http://www.force4.co.uk/4593/Clamcleat-CL261-Power-Grip-Cleat.html or just tie an icicle hitch http://www.animatedknots.com/icicleend/index.php?LogoImage=&Website=

The combined apparatus is so flexible and easy to use that I shall probably get rid of a second permanent block on my 6mm jib halyard, originally installed to give me some mechanical advantage when raising the mast and tensioning it against the shrouds.

Attached a photo of my setup, which will also happily deal with 4mm Dyneema halyards.

[Matthew P]

Thanks Graham, I was thinking about using Prussic loops but I like the look of the Icicle Hitch.  The Karver KJH looks good but a tad expensive for something I will almost certainly lose over the side at some point.  Maybe I can contrive a similar gadget from some redundant cam-cleats, or just pay up £8 and get a Power-grip-cleat.

Claus once showed me how to get the forestay violin-string tight by allowing the long end of the club boom to dangle over the side of the foredeck, tightening and securing the forestay and then giving the club boom a hearty lift to rest it on the deck. The result was scarily twanging forestay tension that takes us back to previous interesting threads about luff and leech tension.
 
Are all your halyards 4mm (not 6mm) on Turaco III?

Matthew
Gladys BR20

[Graham W]

Matthew,

If you see the Karver KJH described anywhere as "floating", that means that it's not committed to a fixed position, as in "floating voter", not as in "won't sink".  In fact, it sinks like a stone. And you're right, it is expensive but I wouldn't be without mine - until it goes over the side.

I no longer use my self-tacking jib, so I'm reliant on grunt to get the jib halyard nice and taut.

My jib and main halyards are 6mm, the spinnaker halyard is 4mm. I also have an occasional forestay which is only 3mm.

[Graham W]

The Karver KJH handle mentioned above thoroughly disgraced itself at Rutland on Saturday by snapping in two under only moderate tension.  As far as I can tell (see picture below) it's made from unreinforced French cheese and is therefore not fit for purpose.  It will be going back to its French supplier.

On the other hand, the handy billy part of the rig tensioning apparatus shown above proved its worth by helping to get the boat back on the trailer when the winch stripped its gears.  Avoid this winch http://www.wilmond.co.uk/trailer/winches/wilstow-1200lb-strap-winch.html

Another thing that I discovered at Rutland is that Dyneema creep (or slippage or both) in the new jib halyard results in an alarmingly slack jib luff and slack shrouds.  I don't at all like the idea of having to keep on climbing up on the foredeck in an F5 to sort this out and if it continues to do it, I shall revert to good old 8mm string for my jib halyard.

[Tony]

Claus once showed me how to get the forestay violin-string tight by allowing the long end of the club boom to dangle over the side of the foredeck, tightening and securing the forestay and then giving the club boom a hearty lift to rest it on the deck. The result was scarily twanging forestay tension
Matthew
Gladys BR20

So, I'm not the only person to miss the input to this Forum from "Llafurio"

[Graham W]

Claus has sold Llafurio to Steve Morton, who sailed her at the Rutland rally http://www.swallowyachtsassociation.org/smf/index.php/topic,850.msg6000.html#msg6000

[Tony]

Hi, Graham,
Oh, yes. I forgot. Been a bit busy recently.
Have you heard the rumours about C.R.'s new boat? Very interested to see how it works out. 

[Graham W]

Tony,

Do you mean something to do with this post in the Wooden Boat Forum?

"I have recently sent a brief to a few designers asking if any would like to get involved in a project for "A sailing dinghy cruiser with oarlocks, suitable for crossing oceans with perfect chance of success. A radical new design aiming at the best possible seaworthiness in a lightweight 2-3 men boat without fixed ballast."
I would be ready to fund the design, and a prototype, trusting to recoup my funding from later sales of plans or ready-built boats.

How is the interest here for such a boat?"

[Jonathan Stuart]

I heard from CR recently, via a rather unnecessary snottagram re finding a photo on our development site. He mentioned he has ordered a BRe and will be taking it for outfitting to a company in Lymington (I think) that prepares ocean rowing boats, etc. Potentially interesting project.

[Graham W]

Sounds interesting - an uprated BRe that (presumably) trades speed and weight for survivability in fairly extreme conditions.  I'm not sure how you would fit two rowing positions into a BRe but perhaps that's not the idea.

We've gone off topic, so as it's an interesting area to speculate about, I've opened a new thread http://www.swallowyachtsassociation.org/smf/index.php/topic,952.0.html

[Graham W]

Back on topic a year later, I have watched string creep in action. I have a new 8mm  (Aramid?) anti-torsion cable for my furler that has to be stretched with 100kg of force for it to reach its normal length before being used in earnest for the first time. Every time I managed 100kg on the Salter scale, it would steadily fall back to 95kg before I tightened it again.  This happened several times before it more or less stabilised.

If this happens to 8mm line, what about smaller diameter high tech shrouds, halyards etc? I think I still prefer wire for the shrouds - I can't be bothered to keep adjusting shroud tension.

[Jonathan Stuart]

Thanks Graham for this timely resurrection...timely because I am seriously thinking about replacing the jib and main halyards on my BRe with 6mm Marlow Excel Racing (which is what Matthew mentioned in the first post). Re-reading this thread it sounds like others have found that a positive switch but is that still the case and are there any other lessons to learn? But I agree with your last point re the shrouds and while this may prove to be an old fashioned view I still feel more comfortable with SS there.

[Julian Swindell]

I've had dyneema shrouds for three years now and no problem with them at all. No stretch apparent. I much prefer them to wire because there is much less risk of getting them kinked. Also much more user friendly when the rig is down and all is loose. I wouldn't go back to wire.

[Graham W]

I still use Dyneema 12-strand for all sorts of things, especially where a splice is needed.  However, where a bit of elasticity (as opposed to creep) is useful, as in shroud or bobstay strops for example, then I prefer Polyester.

I had a problem with my gunter yard consistently loosening against the mast and spoiling the shape of the mainsail as it fell away to leeward.  I suspect the culprit was creep in my cruising Dyneema halyard - either that or it couldn't keep its grip on the horn cleat securing it under tension.  Whatever the cause, I have had much less trouble since reverting to 8mm braid on braid Polyester.

Similarly, I had a small diameter (4mm) braided Dyneema spinnaker/flying jib halyard.  Not only did that tend to slacken off at inconvenient moments but its small diameter was hard on the hands and the jacket abraded much too fast for my liking (or wallet).  I am now back to 6mm braid on braid and have fewer problems with slack.

This may be heretical but after using it for various purposes for two years, I'm just not convinced that Dyneema is all that it's cracked up to be for boats like ours - except when it comes to splicing, where it definitely has its uses.

As for steel shrouds, I agree with Julian that they can be kinked by the unwary and could, if allowed, do damage to your varnished bits and bobs.  On the other hand, having had one mast go over the side for unrelated reasons, I'm paranoid about shroud failure.  Isn't Dyneema prone to UV degradation?  And if so, how can you tell that it is about to let you down?