Thimble in Dyneema eye splice

[tudorsailor]

I currently have an adjustable topping lift that is wire from the mast down to a block and then braid on braid to the clutch in the cockpit

I would like to change as the wire is old and plastic covered. One option is to use dyneema instead of the wire. Am I right that I ought to have a thimble in the soft eye of the 5mm dyneema so maintain the strength of the dyneema by keeping a big radius.

If I am, would a standard thimble do or do I need one of the things from Colligo http://www.colligomarine.com/shop-all/terminator-7-9mm-open-black-1

Thanks

TudorSailor

 

[Tomahawk]

I saw the under stays on the bowsprit of a 40' cat in simple dyneema without a thimble.. (London Boat Show)

10mm dyneema is awful strong!

 

[lw395]

Is this to go with a shackle?
If your shackle is nice and smooth with a round section, then you don't really need a thimble.
If the dyneema will be bearing on something that's rough, angular, sharp, prone to corrosion or anything else non-ideal, then an ordinary stainless or even plastic thimble will help.
Another option I've used successfully is to cover the wearing part of the eye with a couple of layers of adhesive heatshrink. This not only has a bit of abrasion resistance, it also conforms to the fitting and reduces movement of the dyneema, so little to no chafe occurs.

If you want very high breaking strain then expensive thimbles probably come into their own.

 

[DoubleEnder]

I have dyneema running backstays that essentially hold up my rig when on the wind. I use a standard stainless steel thimble and replace the line every 5 years

 

[AngusMcDoon]

Will your clutch grip 5mm dyneema?

 

[lw395]

Will your clutch grip 5mm dyneema?

I doubt it grips 4mm wire terribly well either.
A topping lift only needs a couple of feet of travel.
It's possible to splice on a short thick tail for a clutch and winch, or even lead it to a tackle and a cam cleat.

 

[GHA]

Bend radius shouldn't be a problem, a 'perfect' eye will be twice the strength of the dyneema MBS so even with a 50% loss it will still be close to full strength of the line. And dyneema is so strong even with a massive loss of strength it will likely rip somethng off the boat instead of the line parting. Marlow D12 has an anti UV/ anti chafe coating.

If you want to use the same clutch it's not that hard to splice dyneema onto double braid, that's what I did for a roller reefing furling line. Possible with just a stubby pencil taped to the end to the line as a fid.

 

[tudorsailor]

Will your clutch grip 5mm dyneema?

I have not explained my set up well. At present there is a stainless wire that runs from the top of the mast to a pulley. The braid on braid runs from the end of the boom up to the pulley and back down, along the boom to the clutch in the cockpit. I wish to replace the wire with a length of dyneema. So it will not be going through the rope clutch. It will be a fixed length with an eye at both ends

Thanks

TudorSailor

 

[LadyInBed]

DIY Dyneema Fid - Wood screw into 6mm brass tube
project time 30 mins

 

[GHA]

DIY Dyneema Fid - Wood screw into 6mm brass tube
project time 30 mins

View attachment 78278

Or the cheapo version

Little bit PVC tape required.

 

[tudorsailor]

Or the cheapo version

Little bit PVC tape required.

Or I could print one (if I did not already have a shop bought set) ......... Five minutes to model. 30 minutes to print



TudorSailor

 

[Zing]

Cow hitch the ends if you have room. The extra strength from a cow hitch will offset some or all the strength lost from a tight loop. Thimbles have issues too. They can rust and fail then cut or can fail anyway as they are relatively weak, then they cut. Or go to 6mm. Or pick a strong grade of dyneema. It will loose half its strength in the sun eventually, so factor with that too.

 

[tross]

OK I have the Fire extinguisher ready for when I get shot down in flames.

I never spice a loop into any of my running rigging now days and this is my reasoning. Heavly loaded lines Halyards, etc. normally break at in the middle of the loop, so I use halyard knots instead. This allows me to do several things: as I buy the lines longer that required so I can cut and discard the area of the knot as start again new each year. If the loop does wear and break there is a good chance the remains of the knot get stuck in the pulley / mast sheeve and prevent the line disappearing down inside the mast . I can mouse in eather direction which also allows me swap end and minimise the repeated areas of wear and UV damage.

Tross

 

[tudorsailor]

....Or pick a strong grade of dyneema. It will loose half its strength in the sun eventually, so factor with that too.

I wonder how long dyneema takes to loose half its strength when it is constantly exposed to Greek sun

TudorSailor

 

[Zing]

I wonder how long dyneema takes to loose half its strength when it is constantly exposed to Greek sun

TudorSailor

From what I recall it is between 5 and 10 years. It depends on exposure levels and thickness of the rope. UV will penetrate relatively less far in a thicker rope than a thinner one. It is UV which does the damage. I don't doubt Google will churn up the data.

If under high load then creep will end its life early too, though that should not be an issue in your case.

 

[GHA]

I wonder how long dyneema takes to loose half its strength when it is constantly exposed to Greek sun

TudorSailor

Marlow D12 has UV coating, though even if it loses 50% it will still rip something off before breaking or the polyester will go first.