Mast Inversion - Selden Mast

It is also possible, if the rigging is brand new, that the rigging has stretched slightly. In fact probable.

That might not be the only factor, but it might be a contributing factor. As the caps (I assume they are continuous) are longer than the Ds, they will have stretched more. It would be normal to set the rig up, thrash around a bit then loosen it off and re-set it.

But that does look awfully inverted for stretch to be the only factor.
 
Darrel_Walters said:
Wow so many great comments coming in, thanks so much, My Caps are 10 mm backstay 8 mm D1 10mm D2 guessing 8mm

http://www.jimmygreen.co.uk/item/428/surecheck-rig-tension-gauge

Has any one used this type of gauge before ?
Click to expand...

I have one for the 8mm wires on my rig. It does three different wire gauges by rotating a plastic cam.

Easy to use once I had interpreted the instructions and understood them.

From memory it gives readings as a percentage rather than absolute values. (it is on the boat just now).

I would not be sailing the boat with the mast inverted.

Iain
 
Worked for Proctors (Selden) All rigs were set up using a digital vernier. The space in the turnbuckle was measured between the threads, so get this right first. Your caps need to be tight both on the dock and the leward one hand tight when going to windward.Setting up the caps correctly is crucial. This sets the rest of the mast up. Rake is fake.Moving the base of the mast aft will help with pre-bend. Inters set the mid section ,so not as tight as the caps and the lowers tight but not to tight.So when pulling on the backstay this will help with the forestay . Look at the mast both going to windward and leave the settings the same when on the dock and inspect. Never used a rig tensioner. If you still have problems ask a rigger to span your rig and compare the dimensions of the standing rigging.If the rigger does not know how to do this walk .Your welcome .
 
Hi all I have further news.
I have begged, Borrowed, stole a Loose Guage. I let you decide lol.

I have now also the correct measurements specified by Selden.

The good news is I have the correct wires in the right places

10 mm Caps
10 mm D1
7mm D2
7mm Back Stay

The measurements with the guage gives me the following

Caps 20%
D1 10%
Backstay 20%

This is roughly what Selden has said I should be looking for.

The the only logical conclusion must be that the D2 are taking the strain of the Caps and reducing the tension to the top of the mast,

Does anyone concur

Regards
Darrel
 
That could be possible, you haven't checked the D2 tension so its difficult to say. The first thing is that if the cap shroud tension is adequate then it should be putting some prebend in with no sails on. Have you a pic of the rig at the dockside? Is it dead straight, or has some curvature?

There could be other reasons for the inverted mast: as others have said a short forestay would do this, as would the heel being in the wrong position. You said you have a lot of rack on your forestay - where is it at present? Short as possible or at its full extension?

Also it might be worth comparing the invoice you have for re-rigging - it may give the length of the forestay and shrouds which you can compare to the rig diagram (if you have one).

Do you know when your rigger is coming back from his hols? I would be inclined not to use it until it has been fixed and if the cap shrouds are at their recommended position it could be that the geometry has been adjusted due to the rerig.

Please bear in mind that these are horribly expensive things to go wrong, so I would seriously recommend a professional to have a look. If your rigger has set it up and it fails then hopefully he will have liability insurance to cover it. If you start adjusting things now and it fails then he has a perfect get-out clause as it wasn't his fault. I would suggest that whoever has re-rigged the boat needs to fix it. Stupid question but has it been this way since it was rerigged, or just become apparent recently?

I'm sorry if this sounds a bit alarmist, but I just want to put you in the picture. Have you a local sailmaker who you trust? They're normally pretty good at rig tune as its their business too.
 
I can't see a kink in the mast, if there is then it's a new mast I'm afraid although it can be bodged with a sleeve. There are two possibilities for the inversion. First the inner aft shrouds are too loose and the lower spreader isn't pushing the middle of the mast forward. Secondly, and I think more likely, the forestay is too tight and the back stay too loose. What we did when that happened was loosen the forestay by 5 mm then tighen the backstay 5mm. Keep going until the top of the mast is slightly leaning back. Then check the inner stays they will probably be loose. Using a normal spanner you can't break anything.
 
Hmm Interesting point on the forestay being to short, I do have an adjustable forestay, but to get at it would mean complete disassembly of the Furling system.

I know rake can be fake as it depends on how the boat floats in the water. If you have a heavy digny on the back, rake is going to be more.

Based on normal measuring I haev approx 17 inches of rake (see image)
 
Before you go doing that, and while you have the gauge, I'd get someone up the rig to check your V2 and D2 tension. The way the V1 is connected to the V2 and D2 could transfer all the load to the D2 instead of to the V2 (Cap shroud above the lower spreader). The rig looks very straight and almost inverted with no load on it, though its difficult to see from the pic.

As someone said before, rigging wire does give a bit initially, and the V2 (presumably this runs straight through the upper spreader tip to the hounds) is a much longer piece of wire than the D2, so may have stretched more, which would have the effect that more load moves onto the D2 than it should when the sail loads come on.
You did say the mast looks straight athwartships when loaded though, so this may not be the case.

No harm in measuring stuff but be careful moving anything, and if in doubt don't move it - get a rigger.

If your rigger is back soon, as someone suggested before, show him the photos you posted. He'll know its not right, and should be able to fix it.
 
Cheers Nick,

I found someone with a strong pair of Biceps, who is going to winch me up the mast this evening to check the V2 and D2

I report my findings a little later, I understand what you are saying about the rigger, but its a long and complicated story, not that for a miniute I doubt his skill. But its one of those things I can never pin the guy down to do the job, So I am going to tackle it myself,

I have read as much as I can read, spoke to riggers for advise, even some say chuck the guages in the water and go by eye.

I got some old gentry sailors here, all with there ten pence worth of advise, one tenstiosn his rig, so he cant tighten it any more, so it more like a telegrapgh pole, lol

Will report my findings a little later .....
 
Bit puzzled as to exactly what bits of wire you have holding the mast up. Clearly you have main shrouds but by the look of the piccies, these are discontinuous so its one heavy wire from the chainplate to the first spreader where you then get one wire going into the root of the second spreader and one wire going to the end of the second spreader. From deck level you have forward and aft lowers going to the root of the first spreader.

Is that correct?

The geometry of my masthead rig is such that the distance from the top of the mast to the deck when the backstay and forestay are tensioned is less than the length of the extrusion. To accommodate this, the extrusion is given a forward bow of half the width of the mast section. This forward bow is installed by tension on the forward lowers and the inner shrouds that terminate at the root of the second spreaders. Then as the forestay comes under increased load when beating, it not only has to pull the mast head forward against the backstay but also as it effectively tries to straighten out the mast ity is pulling against the tension of the inners and lowers.

It sounds to me as if your mast is too straight when not under load ie does not have enough or any bow. That could be the result of the forestay being short or it could be that the forward lowers and the intermediates are not tight enough. But as you tighten the lowers and intermediates to give bow to the extrusion the forestay does not need to be quite as long anyway.

Probably best start with the tension guage cos if everything is at the right tension and you have this problem then the issue is the length of the forestay
 
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Forgive me if this is a little elementary, but if there are no stays running forward of the mast and no pre-bend, what did the rigger think was going to happen other than the mast invert?

You can do what the heck you like with the tension of the shrouds and diagonals aft of the mast, but if the stick doesn't have to get longer to try to force itself to go through the dead-straight against the tension of them, it's essentially unstayed in the aft direction between the forestay attachment point and the deck step.
 
Simondjuk said:
Forgive me if this is a little elementary, but if there are no stays running forward of the mast and no pre-bend, what did the rigger think was going to happen other than the mast invert?

You can do what the heck you like with the tension of the shrouds and diagonals aft of the mast, but if the stick doesn't have to get longer to try to force itself to go through the dead-straight against the tension of them, it's essentially unstayed in the aft direction between the forestay attachment point and the deck step.
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If I understand what you are asking Simon. It might seem at first glance with a classic fractional rig that with no inner forestays pulling the middle of the mast forward yet with aft intermediate stays pulling the middle back that the mast must buckle middle backwards under load.
The trick is in the spreaders.They are not made square to the mast but sweep backwards by about 20 degrees or so.The cap shrouds which are attached to the end of the spreaders will under tension push the tip of the spreaders forward so counteracting the pull aft by the intermediate stays. The cap shrouds and intermediate stays usually have common chain plates well aft of abeam the mast. Not too much or the spreader tips will not get so much pressure forward but far enough aft to also stop the mast falling forward. Hence often the rig is set up with no backstay tension. Backstay tension only being applied in strong winds to bend the mast. (at the top but this usually pushes the middle forward as well.)
The disadvantage is that the mainsail will chafe on the stays when eased right out running. The advantage is that there is no inner forestay so tacking the jib is much easier.
Please note this description is so for small fractional rigs but OP rigs is far more complicated. olewill
 
It's exactly right. My rig os the same as the op's and my backstay (adjustable) is loose when we're not sailing.
I can take it off completely and the mast is still fine.
I only put the backstay on just before I think we need to reef the main - it flattens the main removing some of the power.
 
fireball said:
It's exactly right. My rig os the same as the op's and my backstay (adjustable) is loose when we're not sailing.
I can take it off completely and the mast is still fine.
I only put the backstay on just before I think we need to reef the main - it flattens the main removing some of the power.
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Your all over complicating this.

Slacken off all the rigging then with the forestay roughly set say 1/3 onto the bottle screw tighten then v1 and hence the hole cap stay until there's a good bend through the mast from base to head be
careful the d2s don't go tight. As you do this the backstay will slacken and the forestay tighten.

If the forestay is too short then the mast will try to invert when you tighten the v1(cap stay)

Check the level of the lower and upper spreader tips is slighty 'up' and equal. There's a clamp on the upper spreader tips (6/8mm Allen key)

Sit On the spreader and Tighten the d2 stays until the mast starts to straighten out but leaving some bend in these don't need to be very tight. Make sure the masts in coloumn.

Do the same with the d1s remember not too tight.

30 mins after starting you'll be ready to Go sailing. (check then tape up )
 
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