Main Sail Shape
- Thread starter LakeOntario270
- Start date
Curious, why do you want to add leech tension? I don't see a bit of twist in the sail as it is. Agree about draft position and halyard tension.
I’ll measure the camber and twist later today, folks. As Said before, it loooks serviceable, but looks overly full. But the numbers will tell.
But in the meantime, I wonder why several people have recommended the OP tighten the Vang. On a dinghy, tightening the Vang bends the mast which flattens the sail. But on a bigger mast, the only thing the Vang does is tighten the leach, which reduces twist (increases the angle of attack at the top,)
But in the meantime, I wonder why several people have recommended the OP tighten the Vang. On a dinghy, tightening the Vang bends the mast which flattens the sail. But on a bigger mast, the only thing the Vang does is tighten the leach, which reduces twist (increases the angle of attack at the top,)
I totally forgot that I promised to analyse this mainsail! I went cruising for a couple of weeks and forgot all about it.
Here is the analysis (below).
The shape is pretty good, although the draft is a bit deep in the middle. I'd like to see less than 12 degrees in the middle section.
The leech (exit) of the sail is pretty flat, which is good.
The max depth position of the draft is good.
Apparent wind angle is 30-35 degrees, measured at the masthead (but it was hard to see clearly so I don't know how accurate that is.) That's acceptable for 10 kt TWS, but it could be under 30 degrees to the wind for a Catalina 270, I think, with good sails (including headsail), good trim, and good helming,
If this were my boat I'd the mast head windex vanes to 60 degrees, and then try to keep the pointer inside that for close hauled sailing in good conditions. (On my old Catalina 27, the vanes were set at 55 degrees, and we could sail at about 28 degrees AWA or less in 15+ kt TWS without pinching, in moderate chop)
I would say this sail is still very serviceable for cruising in prevailing wind speeds under 10-12 knot. I'd have to see the shape in higher winds to know what it's like at 15-18 knots TWS. This sail probably needes to be reefed a little earlier than a new on that has a more shallow draft.
Note that this is a footed sail, so the outhaul tension doesn't have much effect on depth of draft. excessive outhaul tension will just stretch the foot permanently and create diagonal wrinkles (this sail might benefit from a tiny bit less outhaul tension, Experiment)
Halyard/cunningham tension won't have much effect on draft position either, since the full battens pretty much dictate the draft position.
I would have to see a video of the telltales to know if there's correct amount twist in it. So I don't have any recommendations on vang and traveler position, , but I'm guessing it could benefit from more twist, since it's got only about 3-4 degrees of twist.
[On edit Note that I've measured battens #2-4, rather than draft stripes. So this analysis is based on measurements at 20%, 40% and 60% up from the foot, rather than 25%, 50% and 75% up. This understates the amount of twist in the sail. ]
Here is the analysis (below).
The shape is pretty good, although the draft is a bit deep in the middle. I'd like to see less than 12 degrees in the middle section.
The leech (exit) of the sail is pretty flat, which is good.
The max depth position of the draft is good.
Apparent wind angle is 30-35 degrees, measured at the masthead (but it was hard to see clearly so I don't know how accurate that is.) That's acceptable for 10 kt TWS, but it could be under 30 degrees to the wind for a Catalina 270, I think, with good sails (including headsail), good trim, and good helming,
If this were my boat I'd the mast head windex vanes to 60 degrees, and then try to keep the pointer inside that for close hauled sailing in good conditions. (On my old Catalina 27, the vanes were set at 55 degrees, and we could sail at about 28 degrees AWA or less in 15+ kt TWS without pinching, in moderate chop)
I would say this sail is still very serviceable for cruising in prevailing wind speeds under 10-12 knot. I'd have to see the shape in higher winds to know what it's like at 15-18 knots TWS. This sail probably needes to be reefed a little earlier than a new on that has a more shallow draft.
Note that this is a footed sail, so the outhaul tension doesn't have much effect on depth of draft. excessive outhaul tension will just stretch the foot permanently and create diagonal wrinkles (this sail might benefit from a tiny bit less outhaul tension, Experiment)
Halyard/cunningham tension won't have much effect on draft position either, since the full battens pretty much dictate the draft position.
I would have to see a video of the telltales to know if there's correct amount twist in it. So I don't have any recommendations on vang and traveler position, , but I'm guessing it could benefit from more twist, since it's got only about 3-4 degrees of twist.
[On edit Note that I've measured battens #2-4, rather than draft stripes. So this analysis is based on measurements at 20%, 40% and 60% up from the foot, rather than 25%, 50% and 75% up. This understates the amount of twist in the sail. ]
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I agree that it's worth experimenting with increasing the batten tension, but it's not clear to me that increasing batten tension will be an overall improvement in this dacron sail. Increased batten tension might not get rid of the vertical wrinkles, the way it would with a laminate sail. It might just make the draft deeper and rounder in the leech section. It's worth experimenting, but it might not actually sail better.
The wrinkles are all in the back half of the batten, with none in the middle. Also, the wrinkles are centered above and below the seam just above the bottom batten. So that suggests to me that the cloth is stretched move above and below the seam that at the seam. Wrinkles above and below the batten suggest the same thing to me. When you've seen many badly stretched out fully battened sails, like I have, it's easy to notice see those details.
The first think I would do to that sail is ease the outhaul a tiny bit, to see if I could reduce the diagonal wrinkles eminating from the clew. Then reassess the over all shape.
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Thanks for the info. All I have to do is wait for Winter to go away to try out some things 
. I took the sail to my local loft and as usual they found a bunch of seams that needed fixing. I highly recommend every sailor take their sails to a local loft for an inspection at the end of the season (if you have a season).
. I took the sail to my local loft and as usual they found a bunch of seams that needed fixing. I highly recommend every sailor take their sails to a local loft for an inspection at the end of the season (if you have a season).
So, some observations. What is that large line on the right hand side? Doesn’t seem to be a reefing line as I can’t see anything on the other side. It's nice that the sail is back lit so you can see through it. So, with that line and the smaller lines going up presumably from the dutchman system, the sail does not seem to be free from encumbrances of reefing and furling. Lines seem to be tight...But I’m not admittedly familiar with the Dutchman system...
Looking at the picture more closely, it looks like the line goes through the grommet and down along the leach on the other side. Similarly on the two grommets above, which seem to be connected by the line running between them. So, a furling system and/or a reefing system.
Awesome analysis, Judy. What a gift. Have a great holiday season.
-Will (Dragonfly)
The Dutchman system has two lines that thread through the sail. In my case the line is 400lb fishing line. The system works very well.