Backstay adjustment ideas?

[lustyd]

Certainly wouldn't expect you to slow down to sail together, not even sure yet where we're headed on saturday but we'll keep you updated and I look forward to hangovers being closely missed thanks to cheese on toast!

Back to the thread, I have much respect for you if you know enough to do all that on purpose - my vang and sheet side to side adjustment are guesswork and they are basic controls!

 

[30boat]

This the system I came up with.Excuse the quick sketch,it's late.
It's a 16/1 system and there are two 4/1 tackles linked together on pivoting triangles top and bottom.I've exagerated the width for clarity.It's much narrower than that.
I can bend the mast on my Fulmar with frightening ease with this thing.It's also centrally fitted so it may suit your needs.If you're interested I can send you a better sketch and a photo.Incidentally I made another for the kicking strap and again the boom bends if I'm not careful.Very easy to make too.I've used Dyneema but it's not essential.

 

[William_H]

Another completely different option might be to fiot a high field lever in place of tackle. This will give just 2 options on and off which may suit you. You can make a high field lever out of ss strips. You might need a turnscrew in series so that the adjustment range can be adjusted. I use a high field on the forestay of my fractional rig small boat and it is brilliant at quickly tensioning the rig. make a prototype out of cardboard to get the dimensions right.
By contrast 2 types of racing boat here Bakewell 8 and Foundation 36 each have a box in the middle of the cockpit floor. Out of this emerges next to one another the vang control, the mainsheet control and the backstay control. The backstay has tackles under the cockpit. The main sheet hand works these in unison and with gusts. The backstay tension is particularly imrssive in allowing the top of the main sail fall away with mast bend so aleviating heel. Now I would not want to g to that trouble even though I enjoy racing. My backstay sia simple 4 purchase onto one leg of the Y shaped bottom of backstay. And I rely ona wide traveller rather thna powerful vang.
good lcuk olewill

 

[prv]

Another completely different option might be to fiot a high field lever in place of tackle.

Thanks, that's another interesting idea. I do tend to only use two positions for the backstay - loose and tight - so a lever would be ok.

Pete

 

[Javelin]

prv, can we take a step back, just for clarification sake.
Is this on the Maxi or another boat?
Fractional rig I got but a single set of swept spreaders?
Are there a set of lowers?
Is there a baby stay?

You're winding on backstay to flatten the main and open the leech presumably to depower the main.
Too much weather helm or heeling I'm guessing.
You're doing this to save chucking in a reef and only after after winding on the cunningham.

 

[rob2]

Please excuse me if I have misunderstood which wire is twisting... I suspect that the backstay is twisting, which is unfortunate as there is little you can do about it except replace with something a bit beefier in the hope that it won't do the same! I wonder if you would consider the type of offset tang or lever that used to be popular on dinghy kickers? The advantage is that once set up it wouldn't care which orientation it is in.

Having seen many variations on block and tackle backstay adjusters - and their failures - I would council planning for the day one of the shackles disappears. If the strop were only just longer than required for minimum tension, then should the tackle drop away, it would limit the reduced tension to something vaguely acceptable, or at least enough to prevent dismasting. then a lever to tension the stay with a much lighter tackle as it's the length of the lever that gives the greatest advantage.

Backstay on a fractional rig isn't only used to flatten the main as it also tensions the forestay and stops the jib luff from dropping away.

Rob.

 

[30boat]

Backstay on a fractional rig isn't only used to flatten the main as it also tensions the forestay and stops the jib luff from dropping away.

Rob.

Not on all rigs and it also depends on mast stifness.On my 3/4 rig the backstay tension has very little effect on the forestay tension.

 

[Javelin]

Without running backstays or really high and angled lowers the backstay on a frac rig won't add very much to the forestay if any.
In fact without bend control from the afore mentioned lowers or runners you will actually decrease forestay tension as you bend the mast, forcing the middle forward and slightly reducing the height of the forestay.

 

[30boat]

Without running backstays or really high and angled lowers the backstay on a frac rig won't add very much to the forestay if any.
In fact without bend control from the afore mentioned lowers or runners you will actually decrease forestay tension as you bend the mast, forcing the middle forward and slightly reducing the height of the forestay.

Yep!

 

[prv]

OK, so I did the tests today as suggested by dom.

With the stay disconnected, I attached the tackle and strop to the main halyard. Applied some pre-tension with the halyard winch, so that hauling on the tackle felt about the same as when the stay is there. Result: tackle hauled and eased perfectly smoothly with no sign of twisting.

I then put the tackle and strop to one side, and attached a length of braid-on-braid to the end of the stay. Single snatch-block on the chainplate, and the line led to a winch. Result: as I applied tension, the wire revolved. This wasn't just a vague tendency, it was an immediate and pronounced action, as if the swaged end-fitting were spiralling down an invisible leadscrew. It followed the same spiral path in reverse as I slowly paid out the line.

So, that's pretty conclusive - the wire used for the backstay itself revolves under changing load. I need either 1) a very high-performance swivel, 2) a tensioning system that also provides significant counter-torque, or 3) a new backstay.

None of those sound cheap and easy to achieve

Pete

 

[Javelin]

Still don't know what rig boat its on so to specify sizes is difficult,
however,

4mm 12 strand dyneema will give you 1500 kg and is around 2.30 a metre.
Its light, strong, won't twist, has very low creep and you can run it straight into a purchase system.

As a rough guide a sub 25' boat with a frac rig you can use 2mm, a sub 30' use 3mm and up to 36' use 4mm.

 

[Daydream believer]

Swop the wire part first with a piece of braid on braid in the marina & see if it stops the twist
if it works then you either need a different piece of wire or dynema would be easy
Backstays on fractionals do not carry a great load to support the rig as such( note how slack it can be for running) but do get a load of tension when applying force to bend the mast. The point being that testing with a bit of braid first will be Ok for a one off test
make sure that the line in the tackle part is not twisted, Some cheap braids tend to twist a lot

 

[prv]

Swop the wire part first with a piece of braid on braid

Read post 30. It's the stay, not the tensioning arrangement.

Pete

 

[prv]

Still don't know what rig boat its on so to specify sizes is difficult

Maxi 34, fractional rig with one set of swept spreaders and a pair of lowers to the same chainplates.

4mm 12 strand dyneema will give you 1500 kg and is around 2.30 a metre.

Ok, so that's option 3) in my previous post . May not be expensive, but still not easy as I don't have a decent means of getting to the masthead...

Pete

 

[dom]

So, that's pretty conclusive - the wire used for the backstay itself revolves under changing load. I need either 1) a very high-performance swivel, 2) a tensioning system that also provides significant counter-torque, or 3) a new backstay.

Pete

Oh dear, I was hoping that wasn’t going to be the result. The concern is that non-rotation resistant wire creates a problem in direct proportion to the level of torque induced at its normal working load – it reduces the safe working load of the wire and can damage the swages. I’d recommend:

1. Check the rest of the wire to see if it looks to be of the same constriction, albeit with different thicknesses. It would helpful if you know the name of the wire supplier – but to put your mind at rest I seriously doubt either Maxi, or a professional rigger would have used an incorrect specification.

2. Examine the rest of the rigging for symptoms of rotational forces. Pay particular attention to where the stays connect to chainplates and the mast. The lowers should be easy to access at both ends and what you are looking for is evidence of twist at the chainplate in one direction and in the opposite direction at the mast. If there’s no evidence of rotation, that’s great news as we’re only talking about the backstay.

3. The backstay problem may either be due to incorrect wire specification, or incorrect handing. Steel rope is made up of numerous helical elements, and if these helixes are either forced open or closed by a mishandling induced rotation (e.g. when unspooling) the geometry of the wire is changed, often permanently.

4. Re cost of replacement I’d budget c. £80. Climbing the mast will be easy as you’ll already have 2x lines at the mast head – halyard and topping lift. You could use main halyard as the main line and spi or genny as the safety, if the topping lift is too thin.