Mast Inversion - Selden Mast

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Darrel_Walters

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Hi all looking for a bit advice on my rig, In mast, Selden, swepe back spreaders. sailing @ 17 to 20 Knots the top past of the mast is being forced forward when close hauled. is this just a simple case of winding on the back stay, or is there something more sinister happening.

Welcome your thoughts
Regards
Darrel
 
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That really doesn't look healthy.
Is the rig keel stepped or deck stepped? I'd speak to someone (Selden themselves are very helpful) before winding loads of backstay on - it will not just pull the head aft, it will severely increase mast compression as you do so, which could result in collapse.
I'd be getting someone on board pronto to have a look. Where in the country are you?
Also, has it been this way all the time you have had it? Any rigging replacement (I'm thinking of furling gear being replaced at any point)?
 
Hi,
Its Deck stepped, New rigging 2010, set up by a local rigger, who says that he tuned it all correctly. In the Marina the mast looks fine, but once you start driving the yacht at around 17 to 20 knots this is what happens, after 23 knots or so we are looking at reefing the main and genoa, this reduces the inversions, The yacht is moored in Milford Haven SW Wales
 
Rigging can be something of a "black art". I'd suggest you get a good rigger to set your boat up properly from scratch, and then see what effect that has.
 
That's a definite kink you've got there ..

You have a set of lowers and intermediates (from below the top spreader to the outside of the bottom spreader - are these really tight and the bit above the top spreaders looser?
 
I had something similar. Turned out the root problem was that the forestay was too short. Mine was also set up by a rigging supply company; I had it checked out by the sail-makers Saturn Sails, who offer a rig tuning service. Goodness knows how long it had been wrong; I presume the rigging suppliers simply made wires like for like on the old ones.
 
The problem is we have one rigger down here in Pembrokeshire, spoke to guys in Swansea who will not travel this far our local rigger is on hols, I dont mind chatting with him again, but would like to undertstand in the mean time what exactly is happening and why
 
We replaced ours last year - got a known racing rig supplier to make them ... well - if the racing boys use them they've got to be pretty good!

They are based in Southampton - http://www.rigshop.com/ - might be worth a call ?

Another (local to me) is Martin Leaning - http://www.masts-and-rigging.co.uk/ who did an excellent "tune your rig" session for the Bavaria Owners Association .... although I see you have a Maxi -the mast looks similar!
 
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I have an adjustable forestay, I have 17 inches of Rack, D1 and D2 are slack on the lee side, Tight on the windward side, eye up the mast they look to have the right amount of tenstion as the grove seems straight. I understand I have 15% tension on the back stay ...........
 
Looking at your pics, though its not all that clear, it looks like you have starvation creases on the lower section. I wouldn't have expected to see these with a straight mast, let alone an inverted one, as they normally appear when you have too much bend in the lower section of your rig. Have you some more general pics of the rig, taken from further away?
Nick
 
They are the creases that run radially from the clew to the mast. They're an indication that there is a lot of membrane tension in the mainsail, and generally indicate that the mast is bent more than the luff curvature of the sail. In your case with an inverted mast I'm trying to work out how they are appearing at all. :confused:
If you think about how a sail is supported, the wind pressure loads are taken up by membrane tension in the sail, so the main is pulling back on the mast-track. It would be easier to draw a picture than describe! It could be this tension which is leading to the mast being inverted.
Its not the only reason though - too-short a forestay could also do this, as when the wind increases the headfoil deflects more, and this in turn pulls the masthead forward even more.
There are so many possible contributory factors, and it may not just be one, that I would recommend getting someone to have a look professionally before any damage is done.
 
With no sail up is the mast dead straight?

I might be inclined to agree with not enough tension in the back stay (and possibly slightly less in the lowers), I would expect the mast to bow forward slightly with no sail (pre-bend), this is the only way of resisting forces pulling aft. If the back stay is not tight enough (or the lowers to tight to let the middle of the mast move forwards) there is not enough pre-bend and the middle of the mast is pulled backwards. (unless of course you had a baby stay removed at the re-rig).

I am not a rigger, this is only my opinion from an engineering standpoint, but wanted to make my opinion know so I can say 'I told you so' later.

Stuart
 
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Hi all, a massive thanks to all your input, I have manage to speak to selden and emailed pics over etc. There first view was, do not use the boat, They seem to think that the caps are not tight enough and these should be checked, sending more info to Selden tonight and should have an update tomorrow will keep all informed,

If anyone else has any ideas it would be warmly appreciated

Regards
Darrel
 
Darrel_Walters said:
Hi,
Its Deck stepped, New rigging 2010, set up by a local rigger, who says that he tuned it all correctly. In the Marina the mast looks fine, but once you start driving the yacht at around 17 to 20 knots this is what happens, after 23 knots or so we are looking at reefing the main and genoa, this reduces the inversions, The yacht is moored in Milford Haven SW Wales
Click to expand...

I suffered the same situation when I set my mast up for the first time after exiting the canals of France in the Med. We just loosened off everything again, and gradually tensioned up the rig again, having made rough drawings on the effect of tightening each wire in the rig. I think you will find the the Shrouds to the top of the mast are too loose, the wires to the stub of the upper spreaders are too tight - dragging that section of mast backwards. Its worth drawing the rig out on paper to understand what each bit does.

When its all set up, sailing to windward in 15 knots the lee shrouds should be just loose - ie not drum tight if you see what I mean! The lowers must be very tight on both sides to avoid them jarring as the boat pitches.

I would show the pictures to the rigger who set the mast up and ask him first.
 
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