Slot cut in mainsail?

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Slot cut in mainsail?

Postby burningwizard » Sat Apr 08, 2023 12:15 pm

Probably dumb questions, but:

3048

I just got a new Neil Pryde mainsail, and there is a small slot cut into a reinforced patch near the clew. What is this for?

There is also a small black plastic part sewed to a strap on the clew grommet. It looks like it would run through the boltrope track on the boom. Any ideas?

Thanks!
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Re: Slot cut in mainsail?

Postby jalmeida51 » Sat Apr 08, 2023 3:04 pm

That slot is for a jiffy reef, Tie the dead end of the reef line through the slot around the boom up to the leech cringle down to the block on the boom to the cleat. The luff gets reefed to the reefing hook on the goose neck. The smaller cringles between the luff and leach are used to tie up excess sail when reefed.

The sail slug by the clew should feed in the boom. The slot for the bolt rope.

John
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Re: Slot cut in mainsail?

Postby tomodda » Sat Apr 08, 2023 3:49 pm

Hi @burningwizard!

The Black piece at the clew is easy - it's a slug bail (although I like to call 'em bullets). On your sail, it's there to keep the clew up against the mast, that last little part of the luff. Personally, I prefer my sail with slugs all the way along the luff, instead of a rope (less friction), but to each his own.

The slot is a bit harder to decipher. Do you have reef points? It may be some sort of system for tying the new (reefed) clew to the mast, with a reefing pennant or sail tie. More likely though, it's some sort of system for passing a line from one side of the sail to the other, such as a Cunningham (is there a hook further up?) or slab/jiffy reefing. I'd call the sail maker and find out, please let us know.

Tom

P. S. My "puckish" answer is beer-bottle opener, obviously. Stick the top of your beer bottle into the slot and tack - POP! OK, maybe not what Neil Pryde intended. Call them...

P.P.S Just saw @jalmeida's post, forum wierdness. My comments stand, the slot is - like he said - most likely for slab reefing. But the slug goes into the mast slot, not the boom, IMHO. I still like my luff bottle opener idea... You can beat up to the windward mark and open a six-pack all at the same time! Brings new meaning to "Wednesday Night Beer-Can Racing." :)
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Re: Slot cut in mainsail?

Postby GreenLake » Sat Apr 08, 2023 6:51 pm

My main also came with that slug, I've always suspected it helps with the load concentration from leech tension and possibly makes the clew respond better to outhaul changes.

But I had never seen a gap for tying a reefline around the boom. Saves a fitting. Because of the way mains with boltropes have a foot shelf, there should be little tension so a small slit shouldn't weaken the sail. Learned something new.
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Re: Slot cut in mainsail?

Postby GreenLake » Sat Apr 08, 2023 7:03 pm

@Tom, this time I have to disagree with your analysis. The clew is what we are talking about here and that's at the end of the boom, not near the mast. And it's the clew that sometimes has a single slug, even on sails that otherwise use boltrope. (I admit at first I got turned around somehow looking at the image, but then, like one of those optical illusions, it fell into place).

At the other end of the boom, you need something to fix the tack, so that it stays fixed against the pull from the outhaul. On most boats I've been on that was some fitting at the inward end of the boom, right behind the gooseneck, with a pin or a hook for the tack. Above and forward of it, there's usually a small gap as the slot for the boltrope starts a bit above the boom. (Alternatively, the first slider position). This gap shouldn't be critical, as you also may have a Cunningham near that location, that gets pulled down (and takes the luff tension).

Therefore, that little gap near the tack is sailcloth that's not under tension, so doesn't need to be supported, and the area affected is too small (and too close to the downwind side of the mast) to have any measurable effect on aerodynamics.
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Re: Slot cut in mainsail?

Postby jalmeida51 » Sun Apr 09, 2023 2:48 pm

The reason you use the slot to secure the reefing line to the boom is an eye strap is the weakest link in the system. Of course, if you have slugs on the foot of the sail, you can run the reef line between the slugs to be tied around the boom. If you use a quality eye strap with the proper rivets, I don't think your eye strap will fail due to the sail area of the mainsail.

The sail slug by the clew does go in the track of the boom to the outhaul. Maybe for better sail shape in that area, I had a Niel Pryde main on a Rhodes 19 and it didn't have a slug by the clew.

John
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Re: Slot cut in mainsail?

Postby GreenLake » Sun Apr 09, 2023 4:39 pm

I agree, the slit is genius.

My original sail for the DS also didn't have the slug at the clew; I think a slug there does a better job at handling the leech tension than relying on a few inches of boltrope. I think the load is pretty concentrated there, so it makes sense.
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Re: Slot cut in mainsail?

Postby tomodda » Mon Apr 10, 2023 11:28 am

@GL:

You are indeed right, I got mixed up - clew vs Tack. It's early in the season, I haven't been out sailing yet - my excuse, sticking to it.

My main also has a slug at the CLEW, makes life way easier for outhauling. And as @jalmeida points out, the slit for tying your jiffy reef line around the boom is genius. Gonna do that for my NEXT main (hopefully a ways away...), because right now my reefline ends at an eyestrap. Mine is a good Shaefer strap, screwed in with stainless screws to holes I drilled and tapped myself, everything perpendicular to the load, etc.... This just to say that I was quite aware of the eyestrap as the weak point of my slab reefing system when I set it up, but still... I could have avoided with a simple slit in the sail. Next time...

Tom
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Re: Slot cut in mainsail?

Postby burningwizard » Mon Apr 10, 2023 12:38 pm

I called Rudy, who called Neil Pryde to confirm, the slot is for jiffy reefing.

I found this pic on Catalina's website as an example of how this looks when set up:

3049

On a somewhat related question: for the reef line cheek block and cleat, should I drill and tap-screw the fittings, or learn how to rivet? Aluminum rivets to match the mast material, or stainless screws/rivets (with tef-gel/butyl tape) for strength?
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Re: Slot cut in mainsail?

Postby jalmeida51 » Mon Apr 10, 2023 1:56 pm

Some riggers say to use rivets, while others say use machine screws. I read on Harken's web site, use stainless screws. Don't use cheap aluminum pop rivets. When you compress the rivet the center ( stem ) pulls out of the body of the rivet and you loose strength.
Use stainless steel rivets where the stem gets locked into the body of the rivet. You will need a good hand rivet gun to compress these rivets. Call a spar shop and see what they recommend. I used number 10 machine screws and never had a problem.

John
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Re: Slot cut in mainsail?

Postby GreenLake » Mon Apr 10, 2023 5:16 pm

On my boat, I have an eyestrap that fits at the location where there used to be a horn cleat for the outhaul a few inches from the end of the boom. Initially, I tied my reefline to it. However, it got damaged at one point, and not being able to secure a matching one, I replaced it with an eyestrap, reusing the holes. Because of that I have it set up at 90° to the direction of pull, which is not advantageous. I've used the reef (and have the photo to prove it) but the arrangement so far appears strong enough. It's not using rivets, but I don't remember whether the holes were tapped.

2717

I'm not sure what the maximal expected loads are. The usual way to estimate these is to figure the sail force required to capsize a boat with fully hiked crew.

Image
(from: https://forum.daysailer.org/forum/viewtopic.php?p=36850#p36850)

The 3' estimate of the lever arm in the diagram is perhaps a bit small, let's say a crew can hike to get an effective lever of 4' (and the reefed sail sits lower, so 8'). Those lever arms are nearly 1:2, so the maximum heeling force is around half the weight of boat and crew, or 5-600#.

The total sail force translates into luff tension, leech tension, outhaul tension, that have some component along those three lines and some component in the direction of heeling. That part gets a contribution from where the luff is in the sail track. The induced leech tension should be greater than the heeling force, because it's the addition of the two components, one inline and one across. But the leech is only one of three edges tensioned. I think, in the end, the effects probably cancel approximately, so that we get a few hundred pounds of effective load on that eyestrap.
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Re: Slot cut in mainsail?

Postby burningwizard » Mon Apr 17, 2023 12:46 pm

Thanks everyone for the advice. Here's a photo with the new sail bent on the boom, and the slot in line with the reef point.

3066
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Re: Slot cut in mainsail?

Postby GreenLake » Tue Apr 18, 2023 3:17 am

Nice.
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