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Old 22-02-2015, 17:33   #31
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Re: Cruising Sail Features

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Originally Posted by Kestrahl View Post
Actually tides have very specific instructions for sail designers as to slide spacing. I presume this is due to the track being plastic as opposed to alloy. There is no way around the large stack height with tides track system unless you ignore what tides tell you.

As to the cunningham, maybe you should go take so photos of sail shape on a stiff masthead rig cruising yacht with cunningham on and off upwind. Then computer analyze them, it'll be a learning experience.
General question: In the case of a tri-radial cut main, made from Hydra net, I don't seem to see much shape change with varying halyard tension... certainly not as much as I recall from the days of cross cut dacron sails. So, is that a good observation, or am I fooling myself? Would the same apply to tension applied with a cunningham?

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Old 22-02-2015, 21:27   #32
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Re: Cruising Sail Features

I'm still confused why you would select hydranet. My understanding (and it may be wrong) is that the few spectra fibers you don't really extend the useful lifetime of the sail and given the premium they charge for it, why would you select it?
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Old 22-02-2015, 21:50   #33
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Re: Cruising Sail Features

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Originally Posted by zboss View Post
I'm still confused why you would select hydranet. My understanding (and it may be wrong) is that the few spectra fibers you don't really extend the useful lifetime of the sail and given the premium they charge for it, why would you select it?
If that query is directed at me, I chose that cloth (Hydranet Radial) on the advice of several different sailmakers. In their collective opinion, it offers great shape retention, better chafe and UV resistance than Dacron, no delamination or mould issues and isn't fussed about being crushed when reefing like many laminates are.

I found a sailmaker who was willing to buy seconds and manually set up the cutting machine to avoid the isolated flaws that occur in the seconds. Extra work for him, much better price for me, product sail with same performance as the regular cloth. Sail is approaching two years of age, one and one half years usage, no issues as yet. Only drawback I see is that it is very stiff, and hence difficult to flake, even with a boom bag... slowly getting better as it gets "trained".

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Old 22-02-2015, 22:01   #34
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Re: Cruising Sail Features

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I'm still confused why you would select hydranet. My understanding (and it may be wrong) is that the few spectra fibers you don't really extend the useful lifetime of the sail and given the premium they charge for it, why would you select it?
Hydranet is great stuff. My hydranet jib is 2 years old and looks like new. I'm expecting to get 10 years out of it.

It is expensive.


DP is the only cloth that I will use for working sails. For spinnakers I use Challenge.
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Old 23-02-2015, 04:16   #35
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Re: Cruising Sail Features

Hydranet - just so no confusion, Hydranet is woven hybrid material using Dyneema and polyester (Dacron). It's primary benefits over all Dacron is more strength to weight and lower stretch. These benefits don't really make sense for boats below a certain size - simplistically, if a sail built in all Dacron is big enough to require a leech ply, it makes sense to start thinking about woven hybrid materials (if you have the $$).

Jim - as to your question, yes it's a good observation. Crosscut Dacron sails show luff tension/shape changes very easily compared to high modulus radial sails. Dacron is of course stretchy (especially soft or low modulus Dacron) and compounded on the luff because it's all bias loading (crosscut yarn orientation). An easy-to-acheive bad result of a highly tensioned crosscut Dacron luff when the overall sail load is high (much wind), is permenant cloth distortion (modulus of elasticity reachs material yield point).

Fundamentally the effect of changing luff tension on radial/high modulus sails is the same, just subtler.
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Old 23-02-2015, 21:42   #36
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Re: Cruising Sail Features

I can't even tension the lower part of the luff well with the halyard so have to use a Cunningham, which I love. My Cunningham is a shortish piece of spectra with polyester cover 8mm diameter. It is tied around the boom attachment.

I take it up to the Cunningham cringle, feed it through and then on the other side down and straight onto the mast mounted winch.

When it's time to reef, I unto the Cunningham, feed the halyard back to the marked spot for that reef, pull the sail down with the reefing line at the leach, jam that line with the jammer where the line exits the boom, take it off the winch and then the Cunningham goes through the reef cringle at the luff side and becomes the luff reefline/Cunningham.

I know many have single-line, cockpit operated reefing; the thought alone is stuff of nightmares, I hate it.
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Old 27-02-2015, 21:10   #37
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Re: Cruising Sail Features- Fat Head?

Can someone explain the pros and cons of a "fathead sail"? My cat is a little underpowered as is and I do not have aft backstays to worry about (much like this picture). They do not seem very common so there must be some reason??
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Old 27-02-2015, 22:27   #38
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Re: Cruising Sail Features

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Originally Posted by zboss View Post
I'm still confused why you would select hydranet. My understanding (and it may be wrong) is that the few spectra fibers you don't really extend the useful lifetime of the sail and given the premium they charge for it, why would you select it?
This is true for cross-cut hydra-net. It has so little spectra that there is no performance advantage. Its only advantage is better tear resistance.

Radial hydra-net has a lot more spectra content, I can't remember how much, maybe 40% and is a good step up from dacron.
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Old 27-02-2015, 22:49   #39
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Re: Cruising Sail Features- Fat Head?

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Originally Posted by Sailorman Ed View Post
Can someone explain the pros and cons of a "fathead sail"? My cat is a little underpowered as is and I do not have aft backstays to worry about (much like this picture). They do not seem very common so there must be some reason??
Ed
The reason is most Cats probably were designed before square top mains became popular. The only problem with a true square head is you have to detach the head from the head car, otherwise it won't go in the sail bag. Can be solved by going for a big headed sail that isn't quite square at the top. If you need more area then this might be a good solution. Keep in mind that you may need to reef earlier, as they generate a lot of power up high.
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Old 27-02-2015, 22:56   #40
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Re: Cruising Sail Features

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Originally Posted by Jim Cate View Post
General question: In the case of a tri-radial cut main, made from Hydra net, I don't seem to see much shape change with varying halyard tension... certainly not as much as I recall from the days of cross cut dacron sails. So, is that a good observation, or am I fooling myself? Would the same apply to tension applied with a cunningham?

Jim
Totem explained it. The radial sail has fibers running vertically up the luff, so isn't as stretchy as a dacron sail where the load would be on the bias of the cloth. The cunningham on a stiff rig will pull the draft of the sail forward which is unwanted in a monohull upwind as you lose pointing ability. You can see a photo here from the Melges 24 worlds last year and how loose they run the luff. Catamarans are a different story as low and fast upwind can result in good VMG. And on a bendy rig the cunningham is causing mast to bend thus flattening the sail. The cunningham on a cruising boat is more useful to take the slack out of the luff, than trying to change sail shape.
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Old 28-02-2015, 03:11   #41
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Re: Cruising Sail Features

The shape of a tri radial hydranet sail doesn't change much because the cloth is so strong that it can't change much. Playing the cunningham is by and large a waste of time. Just tension the luff sufficiently to reduce the wrinkles and call it quits.
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Old 28-02-2015, 05:56   #42
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Re: Cruising Sail Features

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The shape of a tri radial hydranet sail doesn't change much because the cloth is so strong that it can't change much. Playing the cunningham is by and large a waste of time. Just tension the luff sufficiently to reduce the wrinkles and call it quits.
As long as you can fold a sail to put it in a bag then it is more than able to change shape with time tested controls like a Cunningham.

I have tri-radial cut sails. I have Hydranet cloth. I have a Cunningham and use it because it works.
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Old 07-03-2015, 03:05   #43
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Re: Cruising Sail Features

Quote:
Originally Posted by Kestrahl View Post
Actually tides have very specific instructions for sail designers as to slide spacing. I presume this is due to the track being plastic as opposed to alloy. There is no way around the large stack height with tides track system unless you ignore what tides tell you.

As to the cunningham, maybe you should go take so photos of sail shape on a stiff masthead rig cruising yacht with cunningham on and off upwind. Then computer analyze them, it'll be a learning experience.
On Cunninghams, it's a bit silly to debate the point, as, put simply. The math don't lie. And besides, they work... in the real world anyway.

Let's say, for instance, that the distance from your gooseneck, up over the halyard sheave, & down to the winch is 100' total. If things stretch 0.1% as the breeze changes, not at all outside of the norm with even less than 10kts of wind speed change.
Then even using a super hi-tech halyard & sailcloth, you're going to see 1.2" of difference in luff/halyard length (or more, fairly easily). Which is definitely enough, in an astute sailor's book, to warrant re-tuning one's (halyard, or rather, to make things FAR easier - Cunningham) trim.

For as the breeze pipes up, I've yet to be on a boat (of any size bigger than a bathtub) where such a change in luff length isn't noticeable. Ergo, my firm suggestion for incorporating a Cunningham.
Put a few small witness marks on the sail & spar if you don't believe the math. They will shift as the AWS changes.

Why one would intentionally leave off this control feature, especially on a style of boat which has less of them to begin with, leaves me scratching my head.

The length (stretch) changes under varying loads, of the involved materials, are easy enough to look up & calculate. And a 0.1% change in length due to stretch is well within reason (if you do). Actually it's a fair bit less than the norm on a lot of boats. Assuming, that is, that you do the math on stretch due to wind changes. Even if you're running the lowest stretch materials which $ can buy.

Regarding stack height, & sail attachment spacing, yes, I've been known to "color outside of the lines" - with, & within reason.
Pretty much due to the Fact that some areas of sails (& the attachment points in said locales) are much more highly loaded than in others. And it rarely hurts to "tune" a main's attachment to match.

Such is pretty easy to visibly see. Just look at the wrinkles & load lines in the cloth in any properly hoisted & trmmed sail. Or for those with Ray Charles's sail load analysis ability, look at the density of load carrying fibers in the various areas in laminated, load mapped, sails. And how a main's primary loads in the middle portion of it have little (relatively) to do with resisting transverse, & or angular loads.

If such information is in doubt, then witness the "stunt" during a certain America's Cup ('92, or '05), where the French team actually REMOVED a good portion of the luff section of their main, & re-used said (measured) area, on the sail's leech. Where it is actually loaded, & generates much more drive.
Or that on a properly trimmed mainsail, a large percentage of the luff is simply lightly fluttering when going upwind (assuming no full battens in that area).

The simple answer is that in some areas, with exception for where the reefs & full battens lay, is that the load on a mainsail's luff is almost entirely generated by halyard tension, period. There's not a lot in terms of wind/trim created stresses being generated in terms of holding it onto the spar (relative to other locations on/in the sail).

Or again, go back to the pre-sail track days, & witness the Fact that slug spacing on highly loaded/performance mains was (and is) FAR higher on the upper & lower thirds of the sail. Even on boats using full on, stainless steel, or aluminum sail slides.
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Old 07-03-2015, 05:12   #44
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Re: Cruising Sail Features

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Performance?

I think the original post about about a "cruising" sail.

While the battens might give you a few more seconds per mile, the battens are often a source of damage to the sail ... something that could effect performance in terms of longevity.

I'm not about to go back searching for a number of sources on this issue(advantages of using no battens on a "cruising", sailboat), but you can ...

As far as the noodles and other stuff ... that's just open pondering that if such a thing could suffice and further, not be a potential source of damage to the sail ... then ... what the heck!
You're giving out bad advice, again.

Battens actually increase the longevity of the sail...that's part of their purpose. They keep the leech from fluttering and wearing prematurely. And full battens are even more effective since they protect the entire depth of the sail.

Not sure where you "read" that battens are bad but I would hunt that book down again simply for the purpose of throwing it out.
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Old 07-03-2015, 05:37   #45
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Re: Cruising Sail Features- Fat Head?

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Originally Posted by Sailorman Ed View Post
Can someone explain the pros and cons of a "fathead sail"? My cat is a little underpowered as is and I do not have aft backstays to worry about (much like this picture). They do not seem very common so there must be some reason??
Ed
The fathead is going to give you a LOT more sail area for the same mast, somewhere around 25-30%. There may be slight efficiency gain that goes with than, but the effect is insignificant compared to the sail area gain.

The downsides:
-More load than the mast and rig were designed for. Probably not a significant issue, just reef earlier as Kestrahl indicated.
-Complexity. With a lot of research about what works on other boats, this shouldn't be too big an issue.
-Cost. Figure about double the cost of a regular main when converting, and maybe 133-150% when doing future mainsail replacements after the initial conversion.
-Change in weather helm. This is likely the biggest problem and could be pretty severe, you are adding a lot of sail aft. If you can change the location of the mast step and change the mast rake this may alleviate some or all of the problem. Adding foresail area might solve the whole problem or at least most of it.
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