Forestay sag...

[Fou Du Large]

Hello !

This afternoon i was looking the sag of my forestay...

18 - 20 Kn wind  about 40 deg. appt. wind ... with tighted luff 135 genoa.
Looking up the forestay... evaluate about 8-10 inches of sag.
Harken furler.
I think it's too much

the tension of my split backstay is 850-900 pounds. On each side. (no backstay adjuster)

Do you think that i have to retight the forestay?

The speed of the boat is OK 6.5-7 Kn. But i'm feeling bad with this sag...
What do you think of ?   


Thank you.

[tonywright]

Fou

Forestay sag is good for speed, but bad for pointing. Depends what you want more of. You get rid of forestay sag by tightening the backstay. Then you will point better, but not have so much speed going to windward. That's why racers prefer to have a backstay adjuster. Often referred to as the accelerator. (If you tighten up you should be able to point about 30 degrees apparent.)

Tony

[Footloose]

A backstay adjuster is on my list of upgrades; however, a recent letter in Practical Sailor talked about backstays failing under the side loads created at the chainplate by the blocks.  This has caused me to rethink my design.  I have not read about this on this board.  Has anyone had their backstay fail using an adjuster?

[Jeff Kaplan]

fou, re-tighten your back stay, you will see a noticeable difference. i had my rigging prof. tuned this season when i needed some mast work, and he cranked down on the back stay toggle more than i ever would. in fact, he bottomed out the toggle and said there was more to go to get a bettter mast rake and wants to cut the back stay and install a new toggle to be able to tighten more. performance has greatly improved...jeff

[tonywright]

If you make a major change like this, don't forget to recheck the engine/prop shaft alignment. These hulls seem to flex quite a bit with changes in rig tension.

Tony

[joe]

jeff, your post said the stay adjustment had caused good improvement. is this in pointing up or in speed or both? can you give an estimate to us in the speed change. thanks. joe

[Ken Juul]

Jeff,
before you redo your backstay check your mast rake.  I think the standard is 2-6" aft measured from the top of the mast to the boom.  If your forstay has never been adjusted it may have stretched enough to allow the back stay adjusters to bottom out. 

[Jeff Kaplan]

joe, to answer your questions, i can't say that the speed has picked up greatly, maybe a 1/2 knot, but the ability to point up is greatly improved. again can't say that i can get 30* into the wind but very close.sail shape, both the head sail and main, has improved greatly.  i think the best way to describe the performance increase, and i think all will agree with the term, the "feel" of the boat is better, tighter. ken, the rigger wants more rake than we can get now so he added a jaw toggle to my schaffer system and tightened it down to be able get more tightening at the back stay turnbuckle, which he bottomed out the terminals and said he wants to cut the back stay, add a new terminal to be able to crank down some more. he is a huge fan of hyd. backstay adjusters and tried to talk me into one, but at this time i declined. other things to spend money on now. the rigger is northeast rigging, kevin, and he always attends the maryland boat shows. look him up next year....jeff

[Ken Juul]

Steve Lyle wrote an execellent article about forestay tension for the Mainsheet. 

http://www.c34.org/mainsheet/pdf/Feb_2004.pdf

I'm a little concerned that you are overtensioning your rig.  His calculations indicate 600# per leg is all that is required for correct headstay tension.  The rig will take the extra tension just fine, however the hull may try to turn into a banana over time.

[Kyle Ewing]

Another advantage of the backstay adjuster is you can easily remove tension when not needed to keep stress off the boat.  Removing tension on other items (outhaul, genoa halyard, etc) when not sailing can reduce sail stretch and increase life.

[Jeff Kaplan]

ken, i don't think he is over-tightening the rig, only setting it to what it is supposed to be. the mast was probably never really tuned by the po, and i have just gotten around to it. i trust this rigger as he knows the catalinas inside and out, along with ever other make. he would not put anything in harms way as he would be responsible for the consequences...jeff

[tonywright]

I looked at the Loos site (they make the tensioning guages). They recommend a 5/16 forestay be tightened to at least 2000 lb (or 15% of breaking strength). Tensioning the backstay split, this would probably be 800-900 per side, since there is more leverage on the backstay due to the wider angle to the mast.  They suggest that most people under-tighten rigging, because they are worried about "breaking something". In fact undertightened rigs cause more damage. Oh and it confirms that the only way to tighting roller furling is via the backstay.

That being said, remember the warning to ensure good lubrication of your threads on the turnbuckles. Forcing dry turnbuckles to turn can cause the "cold weld" effect, and a major repair bill.

Tony