Dyneema instead of bottle screws

dylanwinter

dylanwinter

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Buckingham
www.keepturningleft.co.uk
I raise and lower my mast a lot

and one of the snags with bottle screws is that they often get twisted and bent

this time last year I made the decision to use dyneema instead of bottle screws

two lengths - five wraps each side

one year in and so far so good

no sign of UV degradation yet either



Dylan
 
Dylan,

when raising or lowering my mast I tie the bottlescrews up vertical to the guardrails with elastic sail ties to prevent them toppling.

Personally I'd worry about chafe on dyneema lines, but I'm a born worrier.
 
Dyneema does not tend to fail when exposed to sunlight, but it can shrink!
But if left under tension for a long time it will 'creep' i.e. stretch.
On the whole, good stuff though.
 
Seajet said:
Dylan,

when raising or lowering my mast I tie the bottlescrews up vertical to the guardrails with elastic sail ties to prevent them toppling.

Personally I'd worry about chafe on dyneema lines, but I'm a born worrier.
Click to expand...

The whole lot can be synthetic...

http://www.colligomarine.com/

Just think how much whizzier your boat would be with this stuff. It would be phenominaller.
 
AngusMcDoon said:
The whole lot can be synthetic...

http://www.colligomarine.com/

Just think how much whizzier your boat would be with this stuff. It would be phenominaller.
Click to expand...

Angus,

come on; you know perfectly well the Anderson 22 is hypersonic and couldn't go any faster, I regularly pass SR-71's and Auroras at 60,000 feet.

If god had meant us to use bits of string he wouldn't have given us stainless steel.
 
dylanwinter said:
I raise and lower my mast a lot

and one of the snags with bottle screws is that they often get twisted and bent

this time last year I made the decision to use dyneema instead of bottle screws

two lengths - five wraps each side

one year in and so far so good

no sign of UV degradation yet either

Dylan
Click to expand...

A good traditional solution, but why Dyneema? Tarred hemp should be fine.
 
Dylan
do you tension up the leeward lanyard once under way, or just haul them in as much as you can before setting off, and leave it at that?
 
Mavanier said:
Dylan
do you tension up the leeward lanyard once under way, or just haul them in as much as you can before setting off, and leave it at that?
Click to expand...

never change them

the tension all comes from the forestay - it needs to be fairly tight otherwise the roller reefing does not work

having said that it is a gunter rig so nothing is sweated up really hard

I used to sail eboats and sonatas where everything was bar tight

katie L is a different kettle of fish

I was warned to watch the tight turns on the dyneema

so far it seems very happy and the outer strand of dyneema is turning around the inner one so although the one closest to the shackles turns hard the other turns fairly gently

I was worried to start with but am not feeling fairly confident with it

D
 
dylanwinter said:
....I was warned to watch the tight turns on the dyneema....so far it seems very happy and the outer strand of dyneema is turning around the inner one so although the one closest to the shackles turns hard the other turns fairly gently...
Click to expand...

I'm wondering whether the use of oversized nylon thimbles in way of the shackles might not help the 'radius of bend' issue.....?
 
We use dyneema and variants a lot in paragliders. The trouble with the stuff is once you put serious load on it, the load-bearing core creeps its way out of practically any knot. Hence I would suggest melting a large blob on the end of the line so that it can't creep all of the way out and drop your rig over the side.
 
SAPurdie said:
We use dyneema and variants a lot in paragliders. The trouble with the stuff is once you put serious load on it, the load-bearing core creeps its way out of practically any knot. Hence I would suggest melting a large blob on the end of the line so that it can't creep all of the way out and drop your rig over the side.
Click to expand...
Spliced eye and soft shackle seems to overcome that, but you're right, it's a well known issue.
 
SAPurdie,

I think your wings are even more important to keep sound !

But in that lightweight application Dyneema is hard to beat, like any aircraft needs constant thorough inspection; I have only flown in such aircraft twice and never owned one, would plastic thimbles and marks to show creep help ?

Just to throw something else into the mix, 7 X 19 galvanised wire is a lot more supple than stainless, people automatically presume stainless wire is the stuff to use for the Anderson 22 keel winch, but in fact it should be galvanised 7 X 19, stainless doesn't like a small pulley radius.
 
SAPurdie said:
We use dyneema and variants a lot in paragliders. The trouble with the stuff is once you put serious load on it, the load-bearing core creeps its way out of practically any knot. Hence I would suggest melting a large blob on the end of the line so that it can't creep all of the way out and drop your rig over the side.
Click to expand...
I'd have thought the answer to that would be to just use the core of the line and discard the sheath. Also splice everything possible.
 
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