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Old 06-08-2013, 15:55   #1
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Tighten backstay or forestay ?

Since installing my new Hood Seafurl 5 furler in the Spring, the mid-section swings from left to right and vice versa in say a 5 knot wind, with the sail furled, when the backstay is not tightened, e.g. at the dock or at anchor. I'd say the movement at the mid-section is about 1' each side of the true vertical. I don't see other boats at the dock displaying this behaviour.

Did I not tighten up the forestay enough when I installed the furler ? It's OK when I'm sailing and tighten up the backstay.

I'm suspecting I didn't tighten up the forestay enough because I now have limited thread on my backstay adjuster. However, I did rake the mast back a "bit" when I replaced the aging blocks of wood with plastic in the mast foot holder which sits on the keel. This could account for the lack of thread to some extent.

If I tighten up the forestay too much, I'm going to run out of adjustment thread on the forestay turnbuckle. Then I'd have to remove the Sta-Lok and move it further up the forestay wire. A task that would be difficult with the mast stepped !

I used to leave my backstay "loose" when I left the boat for any length of time, e.g. a week, as I understood this was better than keeping a strain on it all the time. Now I'm not sure. In the meantime, I have pulled the forestay sheets tight on both the port and starboard sides. This moderates the "swinging" of the forestay.

Lots of variables and constraints with this situation !

Any suggestions/comments ?
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Old 06-08-2013, 16:24   #2
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Re: Tighten backstay or forestay ?

If it is new wire, perhaps the forestay stretched more than you anticipated?

FWIW, I think you do need more forestay tension. You shouldn't have to set the backstay hard to stop motion there in 5 knots. However, the bulk represented by the furling sail plus the furler means that it will move some when you yank on it. Not knowing your boat, I really can't qualify that for you. You may notice some headstay sag, as well.

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Old 06-08-2013, 16:57   #3
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Re: Tighten backstay or forestay ?

Thanks. Yes, it was new wire - didn't think of that ! SS 304 1/4", 41 feet. Quite probably a variable !
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Old 07-08-2013, 05:47   #4
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Re: Tighten backstay or forestay ?

Suggest you take up even amounts on the fore and backstay till you are happy. If you run out of thread on the forestay put a bit more on the back if you have to. When doing that you may have to adjust the lower stays to keep the prebend the same as it was (normally straight on a masthead rig).

We have a backstay adjuster and club race which is a bit different. But with the backstay adjuster off for downwind the front is slack enough to take the clevis pin out. When at the dock the adjuster is on enough to stop movement of the forstay/furler/sail.
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Old 07-08-2013, 06:18   #5
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Re: Tighten backstay or forestay ?

Sounds like your forestay is a bit too long....you should be able to have it really tight with backstay adjustment...o'wise..maybe the backstay is too long

Sagging off in 5 knots...its too loose.....

Have you a competent rigger nearby ?...he can advise you..
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Old 07-08-2013, 06:23   #6
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Re: Tighten backstay or forestay ?

Quote:
Originally Posted by macbeth View Post
Since installing my new Hood Seafurl 5 furler in the Spring, the mid-section swings from left to right and vice versa in say a 5 knot wind, with the sail furled, when the backstay is not tightened, e.g. at the dock or at anchor. I'd say the movement at the mid-section is about 1' each side of the true vertical. I don't see other boats at the dock displaying this behaviour.

Did I not tighten up the forestay enough when I installed the furler ? It's OK when I'm sailing and tighten up the backstay.

I'm suspecting I didn't tighten up the forestay enough because I now have limited thread on my backstay adjuster. However, I did rake the mast back a "bit" when I replaced the aging blocks of wood with plastic in the mast foot holder which sits on the keel. This could account for the lack of thread to some extent.

If I tighten up the forestay too much, I'm going to run out of adjustment thread on the forestay turnbuckle. Then I'd have to remove the Sta-Lok and move it further up the forestay wire. A task that would be difficult with the mast stepped !

I used to leave my backstay "loose" when I left the boat for any length of time, e.g. a week, as I understood this was better than keeping a strain on it all the time. Now I'm not sure. In the meantime, I have pulled the forestay sheets tight on both the port and starboard sides. This moderates the "swinging" of the forestay.

Lots of variables and constraints with this situation !

Any suggestions/comments ?

the only adjustment made on the forestay is adjusting the length. usually to set the mast rake. it stays that way. if it stretches, take up the stretch.. all tension adjustment is done with the backstay on a masthead boat. no need to lessen the tension when not using the boat. that notion comes from wooden boats that may hog. forestay sag is normal on all boats. but too much is not good. forestay wag means it is too loose. with backstay tension off, everything should be tight. use a loos gauge.
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Old 07-08-2013, 07:33   #7
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Re: Tighten backstay or forestay ?

Unfortunately, the only local competent rigger I know is far too busy to attend to my small problem.

However, it appears from the replies that most responders seem to think the forestay is too loose, and I agree, so I will tighten it.

However, just to be sure I'll be doing it correctly, here are my assumptions:

1. The upper AND aft & forward lower shrouds will have to be loose. (The mast is keel stepped, and it will stay up OK by itself - from experience !)

2. The backstay should be loose.

3. The sheets to the genoa need to be loose.

4. I will then move the furler drum up the forestay and tighten up the forestay until I think it's tight enough (or the wag is really reduced) or until I run out of turnbuckle thread, whichever comes first. (Actually, I have a 3" forestay extender attached at the moment, which I guess I could remove ?).

5. Move furler drum back into position. Test for wag.

6. Tighten up shrouds.

7. Go sailing and test backstay adjuster.

Everyone agree with that procedure ?

I don't have a Loos gauge - never thought it useful since I have rod rigging on all but the forestay. Also length of wire protruding from the furler foils to the top of the turnbuckle is very short - don't think a Loos would fit in the space.

Thanks everyone.

P.S. I looked up "Hog" & "Sag" on Wikipedia - terms I'd never heard before. I would have thought tightening up the backstay and forestay too much would have led to "sagging" ? i.e. mast pushing down on keel centre, stays pulling up on stem and stern. But then I'm only a poor mathematician, not a structural engineer !!

See WWF: Monocoque vs truss
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Old 07-08-2013, 07:46   #8
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Re: Tighten backstay or forestay ?

As I recall, the key to the fore and aft position of the mast is lee vs. weather helm. The rake of the mast determines how much weather helm you have and will eliminate any initial lee helm.

Here's a write-up from a Bill Shaw paper on tuning Pearson rigs from our 10M days:

~~~~~~~~
Step l. Choose a day when wind is minimum and waves are small. Slack off the main halyard so that the mainsail shackle just clears the deck or cabin top. Measure the distance from the shackle to the after side of the mast and compare this with the number noted on the sail plan (most often found at the top of the mast on the drawing). If this dimension is missing, then a figure of 6" to l2" may be used. If the boat has a strong weather helm, the mast needs to be straightened up. If it has a lee helm, more rake is necessary. You should have a weather helm (not too much), at all times except in gusting conditions. Avoid too much weather helm—it slows the boat and when beating to windward, produces too much leeway. Under moderate conditions, the rudder angle should be about 3 degrees. As you see, this is an exercise in trial and error. Adding to the problem, adjustments of rake may make the headstay too tight or too slack. If either occurs, you need to match turn for turn. For example, if you slack the backstay 3 turns, then tighten the headstay 3 turns, etc. If possible, get a sailmaker to assist
~~~~~~~

Hope this helps.
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Old 07-08-2013, 08:04   #9
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Re: Tighten backstay or forestay ?

Quote:
Originally Posted by Paperbird View Post
As I recall, the key to the fore and aft position of the mast is lee vs. weather helm. The rake of the mast determines how much weather helm you have and will eliminate any initial lee helm.

Here's a write-up from a Bill Shaw paper on tuning Pearson rigs from our 10M days:

~~~~~~~~
Step l. Choose a day .etc, etc, ......................
Hope this helps.
Thanks very much ! I'll measure that and test the weather/lee helm before I do any adjustments. Although I was beating in some pretty heavy weather last week (25 knots) and I didn't notice any change from normal in the weather helm - still, I wasn't concentrating on that at the time !
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