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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 backstay adjustable? most Macs aren't. Do you have a boom vang or Cunningham? Also, is your luff tensioned enough?

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

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.

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.

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.

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

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.

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.

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

I have yet to see if this improves performance, but I also thought it would be good to be able to apply some tension to the backstay. I took a stainless steel "S" hook, bent it 90 degrees, and opened up one of the curves so it would slip over the stern railing. If you don't have a rail at the stern, you are SOL for this fix.

The lower part of the "S" slips over the backstay. I have bent it tighter so it won't fall off. You pull the clip back and hook it over the stern railing, and it pulls back on the stay, providing a bit of aftwards hook to the mast. I also found this will hold the aft lazarette hatch open (but not at the same time)!

Interim,

If you increase tension on the backstay, you are pulling the top of mast backwards. Since the mast is basically the radius of a circle, when the mast is pulled back, it’s also pulling it down all the while bending the mast. Doesn’t that also make the luff looser?

After reading the previous posts, I’m not sure if you said that the sail has been raised to its limits.

Gosh... when I read the title of this Thread I thought someone had gone nuts

Good thing you didn't see the post about polishing the tiller.

"Doesn’t that also make the luff looser? "
Seems obvious but the Luff isn't a straight edge as I understand. It is cut in a curve, so bending the mast flattens the sail, as the mast takes on the same curve as the Luff. I might be full of ---- on this but give it a nod.

I understand. It is cut in a curve, so bending the mast flattens the sail, as the mast takes on the same curve as the Luff.

I need to be convinced of this. I just can’t understand how a curve straighten’s out an edge when it goes from taut to loose.