Mast tension on SO32

[rodgerg]

I was approached the other day by an old salt who advised me that my backstays appeared to be very slack. Another friend has advised me has the tools to test tension however would need to know what they should be.
I must admit I have often thought that the backstay which splits and goes to each quarter does seem a bit slack.
Can anyone help with advice?

Thanks

[MartyB]

Rodger,

The back stay should not be loose per say. Now that I have stated that. lets look at options and what could be going on.

One since you state you have a split back stay, does it have a pulley system you can then tighten the V'd wires together? If not, install something sooner than later. THis can be a crutial item to have in heavier winds etc. IE a back stay adjuster. This can be done with some simple pulleys and rope. harken, Lewmar among others have already designed systems to work with your back stay.

If you have this system, and when at the dock you are loose.....no big! many of us with back stay adjusters loosen while in port, tighten to meet wind conditions while out sailing.

BUT, as your friend noted, one can adjust, and should have the stays and shrouds at a given % of tighteness, along with a certain amount of slant back wards to straight up of the mast, IE "rig tuning". Rig tuning canmake or break one if they have too much weather or lee helm. I pulled my mast a bit forward, lessoned the weather helm I had. Boat sails much better now, and quicker too! Along with pointing a bit better.

As far as tensin goes, most will recomend the wires be tightened to 15-20% of breaking strength. I do nto recall at this time if there is a generic tuning guide on this site. Ihave a pdf for ullman on another computer that I crashed a few days ago. Some of the mast manufactures like Selden, have general tuning guides on their sites. It will take an hour or two if you have never had the rig tuned. You will also need a "loos" guage. This is a tool that will tell you the tightness of the wire/rod you have. HERE is a listing at one place with some of the guage types you may find.

Marty

[tedp]

Two years ago I had my mast tuned in England (Burnham-on-Crouch) and although I don't know what tension they put on the shrouds and the backstay, they said the SO32 rig with its arrow shape should be able to stand up without a backstay. Using a tension gauge they put a little more bend in the mast than it used to have (about 7 cms in the centre), and it has done very well since. The backstay in my boat has a little tension but not too much - it is a thinner gauge wire than the shrouds and I put on the tension with a tackle.

What I found is the mast behaves much better than it did before, in particular the pumping action has gone which occasionally started when experiencing high side winds in port.

I would replace the split backstay by a block and a dyneema rope, and a four-part tackle to one side. That will enable you to put on a bit of tension regardless of the way the mast is set up.


www.009dutch.nl/jeanneau/569_18_04_11_1_22_40.jpeg

EDIT: the SO32 manual says the following (re-phrased by myself in part, due to the bad English in the manual):

- this is a pushing spreader rig, so you will have to tension the upper shrouds before the backstay.
- the rig must be a bit loose when sailing in a 15-20 knot wind.
- after initial setting up (see last guideline) the lower shroud bottle screws should be loosened by 2 turns.
- the backstay must be used to stretch the forestay when sailing on the wind.

Of these guidelines, I think the first and the last are most important, as they concern the backstay. I think the limited tension in the shrouds as given by the manual will result in a rather loose rig with a risk of vibration ('pumping') as I described above. I feel vibration is far more damaging regarding peak stresses than a bit more static tension in a rig.

[Anwen (Deep Joy)]

Ted, what you have written concurs with what the rigger told me when he looked at my shroud and stay tensions - the shrouds and forestay hold the mast up and the backstay tension isn't as important.

The standard SO32 doesn't have adjustable backstay tension, and I never worried about it. Roger, if you want to have some peace of mind, have a rigger look at the rig adjustment, but I suspect your old salt is basing his opinion on older boats which don't have such swept back spreaders, where the backstay tension is much more important.

[j]

Mar 31, 2013 17:48:25 GMT MartyB said:

Some of the mast manufactures like Selden, have general tuning guides on their sites. It will take an hour or two if you have never had the rig tuned. You will also need a loos guage.

The Selden guide is here

Download the "Hints & Advice" pdf.
No special tools are required.

You do not 'need' a Loos guage unless you intend to adjust your rig for the wind conditions on a regular basis.

[rodgerg]

Guys thanks for all your help, much appreciated, especially the guide lots of good info there.

Rodger

[rene460]

Hi Rodger, I have to agree with the comments re the Selden guide, it is excellent. My SO 30i has a similar twin back stay rig. However you will need to rig your measuring stick on several stays together so you can go around them all twice. The method only works when you start from a slack stay. I used lengths of elec conduit taped to the stays at the top and bottom close to swage on the turnbuckle. I then measured the stay extension with a cheap set of callipers between the bottom of the conduit and the top of the swage. Teds advice on starting with shrouds before back stays is because tightening the upper shrouds tends to loosen the back stays by pulling mast head back. I also agree with him that a little steady tension is better than impact loads from pumping, whether aerodynamic or wave action. At the end of the day the loos gauge or similar may be worthwhile as you go around a couple of times as small adjustments are generally recommended. I probably should have invested in the gauge. I eventually did find a rigger who checked all my stays, mast curve etc. and felt no further adjustment was required, so method seems good.
Rene460

[MartyB]

My Arcadia does not have a split back stay, I still find that once or twice a year, I send some one aloft with a tape, to verify the mast is still centered, spreaders are equal distance to the deck etc. Every other month or so depending upon the (importance of) race I am in etc, I will run around with my Loos guage to verify that the stays etc are tensioned where I last left them. I will also check the back stay to verify it is at 12'ish% which is my base count if you will, I then know in my case, how may turns of the back stay adjuster it is to 20% which is the max I try to tighten it down to.

I admit to a degree, while not totally anal about tuning, not like some, but I am more than others. It does help when things are correctly setup for your rig type etc. One can gain some speed, along with pointing ability etc.