Rig Tension, A word of caution.

[Norman_E]

On a post below the instructions given by Selden are recommended. They can be downloaded in PDF format from this web page .

I used these instructions to check my rig after the boat was re-rigged. All the tensions (as checked with a Loos professional rig tension gauge) were much lower than the percentages of wire breaking load recommended by Selden, and professional riggers then tightened everything up for me, but still to well below the Selden percentages. The riggers commented that if they set the cap shrouds at the Selden recommendations I would probably find it impossible to open or close cabin doors. The percentages Selden recommend may work for racing boats, or for boats with rigging of the minimum acceptable sizes, but on a boat like mine where most of the wire is 10mm setting the cap shrouds at a bit less than 10% of break strength is quite enough to keep the leeward shrouds taut in a blow, as has been proved by some pretty strong winds in the last months sailing.

On a cruising boat with a heavy duty rig you will distort the hull if some of the tension settings advised by Selden are adopted.

 

[myoldsailor]

Fairpoint...however, isn't this more down to poor design or weak yacht build? Rather than Cruiser or racer set-up.

Ie. Jeanneau should make stronger bulkheads.

 

[rhumlady]

Is the rigging the correct size as per manufacture or has someone beefed it up?

 

[FullCircle]

Hm.
Virtually every boat I have raced has had some 'fit' difficulties with the internal finish.

Had trouble with the heads door on my Evolution.

If you dont need the extra tension, don't put it in there.

 

[dt4134]

And of course Jeanneau are totally unrelated to any brand that might alledgedly be known as Bendytoys.

 

[FullCircle]

[ QUOTE ]
And of course Jeanneau are totally unrelated to any brand that might alledgedly be known as Bendytoys.

[/ QUOTE ]

In the interests of fairness, well raced Contessa 32s are known as bananas.

Ever seen the chain plates pulling out of the deck on some worthy old tub? yep.

Not exclusive to Beneteau or other Foreign made inferior products, as you imply.

 

[lw395]

Is there actually any advantage in uprating the wire sizes beyond the strength of the hull?
The rules of thumb in the Selden material and elsewhere are consistent with wire whose size has been selected by a consistent design process. If you move away from that and arbitrarily fit stronger wire, I would expect the required preload to be similar.
Having fat wire with less stretch can be a bad thing, as when the mast curves unloading the cap shrouds, all tension can be lost from the lee shroud.
Not to mention weight aloft.

 

[chewi]

Correct rig tension is devised to match the forces involved, so it would correctly be calibrated in Newtons, but that's difficult to measure in a rig, so the guages assume you have an appropriate guage rig. If the rig is oversize then you have to compensate so that you get say the 5mm recommended tension at a lesser percentage of a 6mm rig. ie only approx 2/3rd of the 5mm breaking strain % for 6mm.

As others have said, there is no point in oversizing, it just confuses ands adds weight aloft.

 

[Norman_E]

True, but I think a lot of cruising yachts (at least the ones made a few years ago) have a rig which is heavier than strictly necessary for the sail plan, and I am quite sure this is the case with my boat. I have the short mast with a full batten main and 10mm shrouds, which was the original spec, but I have seen boats with bigger rigs that have 8mm.

 

[myoldsailor]

Norman...thinking about it...agree with you there. I have seen the same.

 

[ytd]

I have never felt happy about the "tighten to 10% of bs " instruction especially for a fractional rigged boat with an adjustable backstay. It may be fine for riggers setting up a new boat but once a boat is "run in" is there any benefit in more tension than is required to keep the lee stays tight in a blow?

 

[lw395]

10mm is not outrageously big for a 45ft boat. I had 10mm main shrouds on a 39ft boat. big rig and deep keel though!
The righting moment of the hull and keel determine the maximum possible force rather than just the sail area.
The best book for understanding the forces involved is 'Principle of Yacht Design' by Larrson and Eliasson (sorry about spellings). Unless anyone has a better recommendation?

 

[30boat]

My caps and lowers are tightened to 25% BS of the 7mm wire.That's the max allowed and the only way I can get the rig to stay in shape.If a rig is oversized the percentage of breaking strength to wich it is tightened has to be lowered accordingly or overloading will occur.

 

[Chris_Robb]

I used to race on my uncles Oyster 41 (steven Jones design). You would wait for someone new on board to go into the heads, and then pump up the back stay - trapping him in the heads! /forums/images/graemlins/laugh.gif

 

[LittleSister]

We set the shrouds on our modest cruiser using the Selden instructions, setting them to the bottom (least) of the tension range Selden suggested.

When we recently had our boat lifted out and mast dropped by the yard, the man told us that our shrouds were way too tight, and that he's rarely come across such tension. It obviously made an impression on him as he's mentioned it a couple of times since.

Given the diversity of strongly held opinions on these matters it's hard for us without them to know where to start!

 

[Norman_E]

The lowest end of the Selden advised shroud tensions would have been way too high on my boat. Cap shrouds at less than 10% are quite tight enough to keep the leeward shroud taut with the boat at more than 20 degrees heel. The backstay however does take about 11 or 12 % of the break strain of the upper 10mm part, split equally between the two lower 8mm sections, and this must put about 15% on the forestay.

 

[VicS]

[ QUOTE ]
On a post below the instructions given by Selden are recommended

[/ QUOTE ] That was me I guess! /forums/images/graemlins/blush.gif

I usually make some noises about not applying the 10% (Even 15% IIRC) rule if the rigging is exceptionally heavy or has been upgraded but did not appreciate that it would be too much for the standard sized rigging used.

I think I said it was the best online guide that I knew. It would be interesting to learn of an alternative.

 

[Twister_Ken]

I used to sail with a man who wrote a book about this. He never used a tension gauge, but we'd spend hours at the start of each season beating, tacking, beating, tacking while he looked at the mast, and tweaked bottle screws. His priority was to get the mast the shape he wanted, and it was that which determined the tension in the standing rigging, not some gizmo. We won plenty of races, so I guess he knew what he was talking about. Either that, or it was my trimming.

 

[William_H]

Why is it so bad to have lee shrouds slack when driving hard on the wind? IMHO it is inevitable so provided the fastenings don't fall out or come loose there is no problem.
If a steel item like a bolt or cable can be given a residual stretch such that when the stress is oscilating on and off it still retains stretch then fatigue (failure) can be greatly reduced. Now in a cylinder head bolt this principle is used to good effect. The bolt is stretched so that pressure pulses from firing will increase and decrease stretch rather than apply /remove.

This principle won't work when a boat hull is involved because the hull itself has too much elasticity. It seems to me to be a principle that works fine in a laboratory but the metalurgist is not a sailor! I may be wrong but this seems to be the only justification for the huge prestretch that some people advocate.

It follows then that if the hull is the limiting factor in how much tension you apply then you can never apply enough tension. It then follows that heavier wire will have a longer fatigue life simply because in service it is stretched to a lesser relative degree.

However I think that rigging wire failure is usually a result of some sort of corrosion failure. Again heavier wire might forestall the failure but not necessarily. So calender period replacement seems to be the safest option. Failures I have seen don't seem to relate to actual usage. But are more common on smaller wires.

So it is not the total tension that matters rather the relationship of the tensions that give the mast a certain shape (straightness under load).
All IMHO if anyone can set me right I would appreciate it. olewill

 

[BAtoo]

All very confusing isn't it.

On my Squib the accepted rig tension is v loose at rest such that the cap and lower shrouds can be pinched together about 1m above deck!!

On my 31' Bene I take the tight rigging approach - a little slack in the leewards at F4ish.

Both seem to work!!