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Bending the mast

Posted: Tue Jun 25, 2019 7:20 am
by Interim
My mainsail is a bit saggy from the luff to the chord. It is not luffing, just a bit untaught on a close reach.

It is a new sail, so this should be a matter of tuning the rig. I think I need to put a little bend in the mast to pull the belly forward and flatten it.

Is the best approach to tighten the backstay?

--john

Re: Bending the mast

Posted: Wed Jun 26, 2019 9:43 am
by THE CUSCUS
Is your backstay adjustable? most Macs aren't. Do you have a boom vang or Cunningham? Also, is your luff tensioned enough?

Re: Bending the mast

Posted: Wed Jun 26, 2019 11:45 am
by Interim
The luff is tensioned enough.

I have a boom vang, used mostly for down wind, but have not employed the cunningham. (sail and mast are rigged; captain has been too lazy to go forward).

The backstay is not adjustable while underway, but the connection at the chainplate has multiple holes so I can change the length of the stay.

I'll try the cunningham this weekend and report back.

--john

Re: Bending the mast

Posted: Wed Aug 14, 2019 8:50 am
by Sisu
Easy enough to make your backstay adjustable, too - just cut it a few feet shorter, re-swage the eye, and add a 4:1 or 5:1 purchase in the space you just created. BWY also sells a kit.

Re: Bending the mast

Posted: Wed Aug 14, 2019 9:26 am
by Tomfoolery
Sisu wrote:
Wed Aug 14, 2019 8:50 am
Easy enough to make your backstay adjustable, too - just cut it a few feet shorter, re-swage the eye, and add a 4:1 or 5:1 purchase in the space you just created. BWY also sells a kit.
Or upgrade your main sheet fiddle block setup to ball bearing fiddle blocks (which BWY also sells, and which I own :) ), and use the old set for the backstay.

If that's not enough, use a single sheave block on the backstay, anchor one end of that line to the tang on the coaming, and use the 4:1 block and fall to the other end of the line. Voila! 8:1 backstay tensioner. 8)

Re: Bending the mast

Posted: Wed Feb 05, 2020 11:20 am
by Newell
Interim wrote:
Tue Jun 25, 2019 7:20 am
My mainsail is a bit saggy from the luff to the chord. It is not luffing, just a bit untaught on a close reach.

It is a new sail, so this should be a matter of tuning the rig. I think I need to put a little bend in the mast to pull the belly forward and flatten it.

Is the best approach to tighten the backstay?

--john
Is your mast straight or pre-bent as in the standard configuration? I have never had a new main sail behave as describe.

Re: Bending the mast

Posted: Fri Feb 07, 2020 1:06 pm
by Interim
The mast is not pre-bent. It bends when I step it and tension the forestay against the shrouds.

The sag I am trying to describe is forward of the maximum draft point. This is where we would get luffing, but it's not luffing. Just saggy.

I'm sure this is an operator error. I suspect I'm backwinding the main a bit from the genny, but I hope I can address it with some combination of halyard, cunningham, and outhaul.

--john

Re: Bending the mast

Posted: Sat Feb 08, 2020 9:27 am
by Newell
Do you have teletales on the aft of your Main? Sometimes in a good wind 15-20 close-hauled and genny quite tight, my main luffs some. My teletales are streaming hard and speed is good. I have pulled the main closer to center to drop the luffing, but it doesn't seem to affect speed. Speed on a X is a relative term. I am usually hitting 4.5 to 5 Knts. :x

I don't know why I asked about 'pre-bent' I think all setup instructions for the X put a bend into the mast. Bending the mast more to flatten the main and fight heel in higher winds is a racing control. I have a split backstay with 4:1 purchase and rarely use it. :macx:

Re: Bending the mast

Posted: Mon Feb 10, 2020 5:31 am
by Interim
Newell--

That makes me feel better. Yes, I have tells on the leech and they are streaming fine. I just look up and see a little soft area right behind the mast, and think that if I can fix it I will get a little more speed. But I think the lift is coming from the after part of the sail, so perhaps I'm worrying about the irrelevant.

Thanks.

=--john