Re-rigging with downsized Dyneema - how small can you go?

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gregcope

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Hi All,

Looking to change to single line reefing on a starlight 35. Present clew reefing point is 10mm braid on braid, with a bowline on the boom.

Looking to replace this with Dyneema/equiv High Modulus. Vyv Cox has 8mm on a similar boat. I was thinking about going 6mm;

- Lighter
- Cheaper
- Less friction
- Size immaterial - this line will not be handled, winched or in a clutch
- Similar breaking strain

Breaking strain logic (from http://www.jimmygreen.co.uk/p/techn...hnical-articles-/rope-breaking-strain-guide);

10 mm braid on braid breaking strain; 2850KG - Bowline will weaken this by 40%, call it 50% => approx. 1425KG
6 mm Dyneema breaking strain; 2200KG - Running loop splice will weaken this by 5%, call it 10% => approx. 1980KG

Thoughts/feedback?
 
Can't fault your logic, if the splice is as strong as you say. The smaller line should reduce the friction even though the dynema is stiffer than braid on braid. I'm assuming that the line is hauled by hand and made off an a cleat, from your comments. Time to go to the chandlers and have a feel of the rope your considering and find out whether you can haul the expected load without amputating your fingers!

Rob.
 
rob2 said:
Can't fault your logic, if the splice is as strong as you say. The smaller line should reduce the friction even though the dynema is stiffer than braid on braid. I'm assuming that the line is hauled by hand and made off an a cleat, from your comments. Time to go to the chandlers and have a feel of the rope your considering and find out whether you can haul the expected load without amputating your fingers!

Rob.
Click to expand...

This line will go into a double ended block. The other end of the block will go to a line that will be handled.
 
gregcope said:
Hi All,

Looking to change to single line reefing on a starlight 35. Present clew reefing point is 10mm braid on braid, with a bowline on the boom.

Looking to replace this with Dyneema/equiv High Modulus. Vyv Cox has 8mm on a similar boat. I was thinking about going 6mm;

- Lighter
- Cheaper
- Less friction
- Size immaterial - this line will not be handled, winched or in a clutch
- Similar breaking strain

Breaking strain logic (from http://www.jimmygreen.co.uk/p/techn...hnical-articles-/rope-breaking-strain-guide);

10 mm braid on braid breaking strain; 2850KG - Bowline will weaken this by 40%, call it 50% => approx. 1425KG
6 mm Dyneema breaking strain; 2200KG - Running loop splice will weaken this by 5%, call it 10% => approx. 1980KG

Thoughts/feedback?
Click to expand...
Not quite happy with your theory
I always understood dynema to loose lots of strength in knots & splices plus i assume the rope goes round lots of blocks ( comparatively to say a halliard)
I would tend to apply a greater reduction figure
Whilst i have dynema halliards i decided not to have reef lines in the same material
I think this is one situation where a small amount of " give" helps reduce shock load on clew reefing point etc
Minimal i agree but does one really need dynema for this
That being said changing 10 mm braid halliard for 8 mm dynema halliard did make a big difference friction wise
 
gregcope said:
Am thinking of doing the same.

Any other comments / issues. Do you find 8mm ok to handle vs 10mm? Any clutch issues?
Click to expand...

None at all. I hoist the main. Half way & the use the winch mainly out of laziness.
I have spinlock clutches & neither the jib or main halliards slip.
I have Hyde sails. & i can put quite a load on them in heavy weather. Having dynema shows up how a small halliard adjustment affects sail shape. This does not happen with braid as it keeps stretching
If the spinlocks do slip then i will just get new jaws. There is also a range of jaw sizes so i could also go down a size if it was a problem. But after 11 years they are ok.
The main on a hanse 311 is not as big as a starlight 35 but not far off as it has a self tacker & a proportionally bigger main for the boat size.
 
On my 34 footer I use 4mm dyneema for the sections I don't handle and 8mm braid on braid for the sections I do.
I use high load ss blocks which takes the 4mm rope.
The system works so well I've now fitted it to three other boats here.

This applies to reef 2, 3, and 4
For reef 1 I use 8mm braid on braid.

I aim to change to all cruiser dyneema next year,
The sections I don't handle I'll remove the cover and taper the line.
 
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Daydream believer said:
Not quite happy with your theory
I always understood dynema to loose lots of strength in knots & splices plus i assume the rope goes round lots of blocks ( comparatively to say a halliard)
I would tend to apply a greater reduction figure
Click to expand...
Knots reduce the strength of Dyneema significantly.
A proper splice retain 95% of the strength in the rope.
Soft shackles and splices work fine with Dyneema.
 
knuterikt said:
Knots reduce the strength of Dyneema significantly.
A proper splice retain 95% of the strength in the rope.
Soft shackles and splices work fine with Dyneema.
Click to expand...

That was the logic of my working.

From marlow "A good splice using the recommended method should not reduce the strength of a rope by more than 10%."

http://www.marlowropes.com/splicing-home-page.html

Not sure Dyneema would be affected any more / less than other cordage.
 
Javelin said:
On my 34 footer I use 4mm dyneema for the sections I don't handle and 8mm braid on braid for the sections I do.
I use high load ss blocks which takes the 4mm rope.
The system works so well I've now fitted it to three other boats here.

This applies to reef 2, 3, and 4
For reef 1 I use 8mm braid on braid.

I aim to change to all cruiser dyneema next year,
The sections I don't handle I'll remove the cover and taper the line.
Click to expand...

Interesting.

Sounds like you use 4mm where I was proposing 6mm.

Javelin said:
The sections I don't handle I'll remove the cover and taper the line.
Click to expand...

Just to confirm you taper by removing the cover? Or do you do something over/above this?
 
simonfraser said:
As said, the shock loads using dyneema are higher.

I busted a reefing point on my main that way, now has further reinforced straps.
Click to expand...

Have you a tri (from the picture) with a big main?

I will have 8 or 10 mm braid on braid on the other end, so there will still be a bit of "give".
 
bitbaltic said:
We went completely to Dyneema last winter on a 30 footer with a comparatively big rig. All halyards in 8mm all (2x single line 1x slab) reef lines in 6mm. Absolutely no handling or strength problems and no clutch problems with older spinlock XTS.
Click to expand...

This is very similar to what I am thinking.

I would keep the third reef as/is now, ie move the 2nd reef to 3rd and keep two slab braid on braid lines and replace reefs 1 and 2 with single line as per Vyv Cox design where the clue is 6mm Dyneema to a double balance block, and from there 8 or 10mm braid on braid or Dyneema back to cockpit clutches.
 
With Braid on Braid the strength of the core and cover is roughly 50/50

With covered Dyneema the cover is just a hard wearing cover that a hand, winch and clutch will grip.
However the core accounts for 90% of the strength.

To reduce friction, weight and to use smaller (cheaper) blocks we taper the covered Dyneema from 8mm to 4mm.

I use cruiser Dyneema from English Braids and have been very impressed so far.

See this video to see how to taper. https://www.youtube.com/watch?v=vWKpnIsX9vI

Keep in mind the breaking strain of 8mm Cruising Dyneema is 2500kg and 6mm is 2000kg so if your clutch, cleat or winch can take it then 6mm with a 3mm core might be even better.
 
Last edited:
gregcope said:
That was the logic of my working.

From marlow "A good splice using the recommended method should not reduce the strength of a rope by more than 10%."

http://www.marlowropes.com/splicing-home-page.html

Not sure Dyneema would be affected any more / less than other cordage.
Click to expand...
Dyneema and knots is a bad combination, knots have a tendency to slip or weaken the rope.
Proper splice in Dyneema is good.
 
I'm using 8mm dyneema on my 2 x single-line and 2 x leech tails.

Strength is not the question, handling is. I tried 6mm and found the jammers wouldn't work consistently and it was difficult to grab. The 6mm now replace wire for guard-rails.

Come to think of it I have no no non UHMWPE in my running rigging.
 
One thing to bear in mind with using smaller ropes than formerly used is that the thinner line might jump off halyard pulley sheaves and jam. The performance of clutches will need to be borne in mind.
 
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