Help with setting up rig

[SvenglishTommy]

I'm having some trouble setting up my rig, I have read the Seldon guide which was very helpful, but there are still a few things I'm not sure of. My rig is a masthead rig, one set of inline spreaders, keel stepped mast, aft lower shrouds and a baby stay.

As far as the cap shrouds go I think I'm ok, although the main shrouds are 6mm and the lower shrouds are only 5mm. My first questions is 'is this normal?' and does it have an effect on how tightly they should be tensioned? (15% of breaking load sounds like an awful lot)

Secondly, how tight should the baby stay be? I know it is there to provide 'slight positive pre-bend' in the mast, but how tight should it be to achieve this. Also, the baby stay is currently unavailable due to the deck fitting passing away last season, is advisable to sail without it until I get around to fixing it? I'm a little worried at the moment as there is slight negative pre-bend without any real tension.

Finally, the forestay is not adjustable as it is an aluminium furling foil. So how do I adjust the tension? The backstay is a single wire until about 2 meters before the bottom, where it splits in two and is adjustable, there is a turnbuckle between the single line and the split as shown here...

How much tension should I apply using the turnbuckle with the udjuster in its most open position.

Any advice greatly appreciated.

Tommy

 

[Tisme]

!5%-20% tension is quite normal so there's no need to worry about that.
Thicker caps than lowers is also quite normal.

There was a thread about split backstay tension in the last week or so. If you can find that it may help.

Sailing without the baby stay in position? I would only do so in light winds, upto maybe F4 at most. When the wind pipes up the loads increase dramatically.

Beyond that I can't help; my boat is fractionally rigged.

 

[john_morris_uk]

Not familiar with the boat you have but here goes:

15% of load for the shrouds isn't that much - but you could start at 10% of load and see how the rig looks.

The lowers will usually be tensioned a little less.

Assuming that the forestay foil is the correct length giving the correct mast rake, then as you have correctly assumed, the forestay tension is entirely dependant on the backstay tension. How tight it is when the backstay is slacked off depends on the amount of adjustment you have in your backstay. For efficient upwind work, in most boats the forestay needs to be VERY tight. I would suggest that you shouldn't compromise too much on this.

As for sailing without a babystay, you might get away with a very gentle sail in very light airs, but don't hunt me down and sue me for this advice when your rig falls down. You should not have an inverted mast, and the baby stay keeps the mast bent the correct way and in line. Mend the fitting!

Don't worry too much - some might argue that so long as the rig doesn't go floppy when you are sailing, you might not win any races, but the mast will stay up.

 

[SvenglishTommy]

Ok, so I'll tension the shrouds to 10% (which will mean the lowers are applying slightly less force due to the lower breaking load).

What about the backstay? I can do the maths to get the tension how I want on the main backstay by measuring the two splitters, but how tight? Would 10% be a good starting point for light winds, then I can tighten up with the adjuster when the wind picks up (and I've fixed the baby stay)

 

[john_morris_uk]

That is an impossible question to answer as we have no data as to how efficient or over what range the tightening mechansism works.

You will need to end up with the forestay at maybe 15% of breaking tension, but some backstay tensioners have quite a wide range of adjustment.

Lots of fractional rigs have very floppy backstays when the tension is off.

We don't have a backstay tensioner on our crusing (masthead) rig, and I wind the bottle screws up fairly tight!

 

[Salty John]

As others have said, 15% is not excessive. I would think that if you slack off to 10% you're leeward shrouds will look very floppy on the wind and you won't point very well either.
Glad you fixed the babystay.
Your forestay is tensioned via the backstay and is adjustable, so a slacked off setting of around 10% might be ok with the ability to crank it up tight with the backstay tensioner. If you can get a gauge on the single part of the backstay, before it splits, use that as your measuring point. If the "legs" after the split are discontinuous make sure they are equal length, equal tension. If they are continuous, running over a sheave, they will equalise themselves.
There is a basic guide to rig tuning with the Loos gauge on my site.

 

[Strathglass]

[What about the backstay? I can do the maths to get the tension how I want on the main backstay by measuring the two splitters, but how tight? Would 10% be a good starting point for light winds, then I can tighten up with the adjuster when the wind picks up (and I've fixed the baby stay)

[/ QUOTE ]

The backstay is a more dynamic adjustment which you can vary depending on wind strength and wind direction.

When you are sailing upwind tighten the backstay and it will tension the luff of the foresail and you will point better. More tension in higher winds but just enough to keep the luff reasonabely straight.

Off the wind you can let the backstay off a bit and it will induce a but of a curve into the forestay which will make the sail fuller and give a bit more power. BUT remembet to tighten the backstay up when you turn upwind or you will wonder why you can't point.

There is no real need to quantify fore and backstay tension as they will be changing all the time.

 

[SvenglishTommy]

Thanks for all the tips guys. This rig tensionning stuff is all very new to me. To be honest the thought of how curved/straight my luff is has never crossed my mind, but at least now I know what my backstay tensionner is for.

 

[VicS]

[ QUOTE ]
the main shrouds are 6mm and the lower shrouds are only 5mm.

[/ QUOTE ]A little niggling worry here. If the cap shrouds are 6mm because they have been replaced with heavier wire than the original tightening them to 15% of the UTS might overstress the hull and chain plates. You will see in the Selden guide that there is a big difference in UTS between 6mm and 5mm (27kN and 19kN respectively). 6mm seems a touch on the heavy side for 28ft but if it is a heavily built boat then fair enough.

Perhaps you should do the test also mentioned in the guide. Namely sail close hauled in say F3 then the shrouds should just start to go slack at 15 to 20 degrees heel. If they are still tight at 20 deg. then they are probably too tight.

 

[geoffatstanpit]

My previous boat, a Seal Sinbad, had that type of rig and the baby stay was a bit of a problem. It was very important to keep it quite tight to stop the mast from bending back in the middle, especially when reefed and the leech tension acts from lower down the mast. The Sinbad also had the problem that the babystay fitting was in the middle of the foredeck only a foot or two ahead of the mast - an area not well supported and giving an inefficient angle to the mast. When beating into a chop I'd wondered why the forecabin got all wet; the babystay was lifting the deck and opening the back of the forehatch seal. I cured it with a substantial beam of Ali angle right across the forecabin ceiling.

 

[nickpaulley]

as a last resort ring up a rigging firm and get them to do it right and then take note for next time - that is what we did and i think it cost about £50 but i didn't pay the bill (shared boat and I don't have the cheque book!) so it didn't feel too painful and we got a set up rig!

 

[SvenglishTommy]

Just to update.

Thank you all for your advice, I finally tensioned the rigging yesterday. I used the 2M rule and vernier calipers method which turned out to be much easier and more acurate than it sounded. 10% of breaking strain didn't feel as tight as I thought, so I went for 15%. I set the baby stay to 15% to get the pre-bend and then straightened the mast with the lower aft shrouds and put the backstay at 10% with the adjuster fully up.

I was really surprised when I took her out for a sail afterwards. I didn't think I would notice any difference in sailing compared to last year, but the rigging tension must have been incorrect before as the difference is very noticeable. She points better, and I'm sure my grubby old genoa didn't set so well before. The helm feels more balanced and it seems I have the correct amount of weather helm.