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Dynex and tight bends


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KM will probably answer this.

 

How does Dynex go round tight (but smooth rounded bends? - the use is 4mm Dynex sidestays for a rotating prod. Splicing a block on just aft of both sides of the spreader 'wings' for a 2:1 on a 1250mm long rotating prod on an E7.4. The 2:1 terminates inboard around the anchor locker area, through the block then aft to block/cleat on each side.

 

Is it cool to go round the pin on the block (approx 8mm pin, no less, decent sized high load blocks) or do I need a thimble?

 

Thx in advance

 

EE

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If it's just a normal SK75 you really want around a 6-8 times the lines diameter, 10 is better and 5 about the minimum. A thimble would be better or you could bush the pin out, that would be the better and cleaner option. Maybe get a 20mm sheave and make a solid thimble out of that.

 

If it's a cooked SK75, more than the above is best or at least the same. This stuff is a lot fussier.

 

But saying that you'll probably be fine just around the pin. We see stuff like that a lot and it's knot busting here there and everywhere every 2 mins.

 

The tighter the radius will mean a reduced life span, reduced strength and more prone to failure especially under shock load. Don't forget Dyneema/Spectra/Vectran and most of that ilk will knot give you any warning it's about to go badly tits up. If you're quick, real quick, you may just see a sudden elongation of the rope in the second it goes bad. If you do see that super sudden stretch happen, duck fast.

 

Basically it comes down to just how much you don't want a failure in a specific spot or application. If it's mission critical and will cause a mammoth cluster f*ck if it busts don't shortcut. If it's only holding the Mother-in-law aboard, do whatever is easiest.

 

I wouldn't go straight around the pin if I was doing it on my boat, probably just a thimble a strong one. Just be a right bitch to get a good gust 1/2 way to Little Barrier and then getting the genny wrapped around the rig after the prod fails.

 

In this case you've got to ask yourself one question: 'If I leave off that 10 grams of thimbles, do I feel lucky?' Well, do I punk?

 

Sorry Clint.

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Ta, thought so.

 

Not huge loads on the EE but yes thimble it is.

 

I think that makes you the first to post a legitimate non thread drift reply on the new forum - congratulations. You are a man for firsts.

 

EE

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Ta, thought so.

 

Not huge loads on the EE but yes thimble it is.

 

I think that makes you the first to post a legitimate non thread drift reply on the new forum - congratulations. You are a man for firsts.

 

EE

 

At times your boat could just about be all hanging off the prod, well knot the entire boat but I think you'll find the peak loads can be well above what most would be thinking. Get a big bullet with the big genny up with low hull velocity and where are the loads going while the hull catches up? A lot thru the bits and bobs holding the prod to the bow.

 

Have a suss of the Prods around a marina and just see how much gear has upsized and/or added after a few sails with the new 'sweet as' (at the time) prod. I know a 31ft boat very similar to mine didn't take long to upsize his prod sideways adjustment strings from 6 to 8 and we have just gone 10mm, the same size as I use as the kite brace on my vessel. Big power reach and the creep from the smaller sizes was a bastard. Direct as in 1 to 1 via good sized spreaders and I doubt there would be much way to fit more than an extra 0.5 sq mt of kite cloth up there, she's a BIGGIE being flown at times. His runs back to a turning block then to a winch.

 

Don't forget the sideways prod adjustment does just what a kite brace does and we know how those can load up large and creep annoyingly at the odd time.

 

I think you'll be fine EE being a light fast accelerator... err at least your boat is, but I think I'd have just quietly ticking away in the back of my head 'If I do have to upsize my string can I easily with this set-up?' Just a thought.

 

6mm Bobstay I think you were targeting. Good call, they can get some big loads at times.

 

2 post in a row now, I'm trying ;) :D

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Here you go....went for the 6mm and thimbles as advised KM.

 

Prod is 60mm dia 4mm wall thickness x 1250mm long or 1325mm long incl the rotating bracket which bolts into the forestay fitting. Will be a 6mm bobstay as well.

 

All up weighs in at 2500 gm including brackets/blocks etc.

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:lol: :lol: All looks bloody good but where's the boat or is it knot really a prod and the missus is now smiling like never before? :lol:

 

If I go turbo I know who's making the prod :thumbup:

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Yes KM I do intend to use it on the yacht as well. :oops:

 

Lets do some performance testing prior to going into full commercial production...... and the number of hours it has sucked up I would hate to give you a number to build another.

 

So if I give a really accurate measuremo for the Bobstay and you do your super prestretchy thing can you give me an exact length that creep will be absolutely minimal on or do I still need to allow for a little adjustment/movement. i.e. after pre-stretching will it move much ??

 

The sidestays can creep a bit as they are in constant adjustment anyway

 

EE

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That is nice EE.

 

there are however issues with thimbles.

 

we now use a ferrule instead.

 

the open end of the thimble can be murder on the dynex, especially if it twists around a little, as it can sometimes do.

 

The sailmakers thimbles are better, as they are continuous but with both types of thimbles they will squash at any load close to half the break load of the dynex. Over time this squash develops into the thimble cracking and wearing out your dynex.

 

if you use a thimble it needs a little s/s brace welded inside it.

 

The ferrule solves the problems as it is way stronger than a thimble and gives a nice rounded eye to lash through.

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Thanks Mr Wolf, I'm hoping at wont be a problem and given I can inspect everything when she goes on the trailer rather than needing a dingy to get a close look I will do a bit of monitoring to keep an eye on it.

 

I plan to remove the prod to keep it out of the sunlight so I can hopefully keep a good eye on it.

 

Fractional genny is about 50sqm so the loads wont be mega huge.

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I was thinking more solid myself, thimble wise hence the chopped sheave comment.

 

As they are a lot cheaper than these babies we have. They are sexy though.

 

Any sign of excess deforming the thimbles fitted and we can tweak.... or tell EE how to at least :D

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mmmmmm - very nice.

 

Yes - I will go that way once I have destroyed the thimbles on there. Not too much drama to replace :)

 

Thanks Guys.

 

EE

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Yeap, easy to swap out if they need too. I know how much you love that splicing lark and probably want too just for fun...... you sicko :lol: :lol:

 

Interesting to see Mr Wolfs fancy toys also come from Italy. Maybe they 'just don't do' normal blocks there :) :)

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Mr Wolf, I get what you mean about the rings now, nice and simple, loose the weight/complexity of the block on the spreaders which would be really nice. It just needs hi-load, low friction as its very little line speed or length when tweaking the prod.

 

It will be in the next iteration of the rigging of and/or new prod continuum....

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Cheers Murky and Croc. Yes just fractional gennys at this stage.

 

Need to bang a decent backstay on before we go too crazy :)

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