Storm jib

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Re: Storm jib

Postby talbot » Tue Apr 23, 2013 12:46 pm

Yes, local conditions here are reported in mph.
Data from the airport (about 3 mi away) showed wind speed of 22, gusting to 28, during the time I was sailing. So I'll knock my claim down from 31.

Sea state was of no use. Normally the wind is W to NNW, with a fetch as long as 4 miles across the lake. You can make a rough wind-speed estimate by the number of whitecaps and size of the rollers. Yesterday the wind was NE, right off the shore. Furthermore, it was gusty and erratic. The water surface never developed waves on our side of the lake; it was more flattened down, as if someone were aiming a hair dryer right at the surface.

I like the idea of the wind gauge on the boat. Now I want one. Also a good GPS. Using the local yacht club's Olympic Circle race course (.5 mi from center to any buoy), you could identify a windward/leeward course and use the instruments to create a cool data table. Well, OK, only if you think data tables are cool. Personally, the prospect of sailing back and forth all day over the same 880 yards, constantly changing sails and entering numbers on a chart, just fills my heart with joy. See, I've already started it.....

Main Jib Wind Tack Angle Boat Speed Time to Buoy
Full Working mph or kph degrees mph or kph minutes
Reef1 Working
Reef2 Working
Reef2 Storm
Reef1 Storm
Full Storm
Full None
Reef1 None
Reef2 None
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Re: Storm jib

Postby K.C. Walker » Tue Apr 23, 2013 12:49 pm

I should get one of those wind meters to calibrate myself. I think I had pretty good estimates prior to being told that I was overestimating.

I've got Walker's book on sail trim and have reread it. Which one did you get? I have a couple of Frank Bethwaite books on my Amazon list, which one did you get and would you recommend that one.
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Re: Storm jib

Postby talbot » Tue Apr 23, 2013 2:52 pm

I only have Wallace Ross' SAIL POWER. Mine is (c)1973, the same year my boat was built. (That should make it more accurate for my boat, right? Or would it only be accurate for winds that were blowing in 1973?) It is already much, much more than I can absorb. I read maybe a page a night, and then ponder the information in my dreams.
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Re: Storm jib

Postby GreenLake » Tue Apr 23, 2013 6:56 pm

Hand-held wind meters run around 100-150. They are fun toys. You will find lots of uses for one :)

Stuart Walker: "The Sailor's Wind", I think, is the title, he's rewritten this book at one point, and I've read both editions. Can't say which one I like better.

Bethwaite includes weather info in "High Performance Sailing" and possibly also in his second book (can't recall, they are both worth their while anyway).

Some other authors have tried to distill the information from these books into something more manageable. "Wind Strategies", I think, is one of the titles, can't think of an author right now. It's a thinnish volume.

One of the problems I've had with most of these books is that they are coy about scale. That is, while you often get very accurate numbers for elevation of certain weather phenomena, the usual horizontal extent of them is not always discussed equally explicitly.

I don't know whether matching a book to the age of the boat is really the way to go. In some sense, yes, because reading about carbon masts isn't going to give you practical knowledge about tuning a DS. However, the early '70s saw the break-through of more correct (and better reasoned) aerodynamic explanations, going back to the work of Arvel Gentry. (http://arvelgentry.com). Older books are more likely to contain outdated theories (although they can be found in more recent books - the old aerodynamic folk myths have an extreme staying power it seems).

Anybody who likes older books that still haven't been fully replaced by more modern works could always read C.J. Marchaj's books. They are rather dense and full of interesting graphs and tables. Consumed a page at a time they are good for many dreams.
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Re: Storm jib

Postby talbot » Wed Apr 24, 2013 12:44 pm

It appears that Ross published right at the point of the theoretical revolution. He has a section on aerodynamics that starts out by saying many old theories have had (that is, as of 1973) been replaced, and he includes wind-tunnel images of airflow to show what actually happens around different sail configurations on various points of sail.
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Re: Storm jib

Postby talbot » Sun May 05, 2013 1:59 am

I got my wind meter (Brunton). Today was 8-12 knots right out of the north (well, magnetic north). I went back and forth from the #5 (South) mark on our local Olympic circle race course to the center with the JY15 jib and the main reefed single and double. Each half-mile run from center to buoy was about 6 minutes, and each two-tack beat up to the mark was about 10 minutes.

Here's what I found: The JY 15 vastly improves performance over using just the main alone, but I couldn't get closer to the wind that about 60 degrees. Any closer than 60 degrees and the luff starts to be taken aback. I could bring the main in closer, but It wouldn't matter because I would still backwind the jib. Could I sheet in tighter? I doubt it. The jib blocks are only 14" off the centerline, and if they are pulled in all the way, the sail is stretched flat and creases across the foot.

Conclusion: For $130 (new from Intensity), the JY15 jib as a DS storm sail is not a bad investment. Sailmaker's Art in Oregon said that for them to do a custom storm jib would be minimum $300. I'm not going to replace it anytime soon. However, I would be very interested to know if anyone finds a 75% jib for a DS that will point higher than 60 degrees off the wind.
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Re: Storm jib

Postby GreenLake » Mon May 06, 2013 2:16 am

Did you check the fore-and-aft location of your fairleads for the JY15 jib?
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Re: Storm jib

Postby K.C. Walker » Mon May 06, 2013 8:46 am

Talbot,

I'm just thinking out loud here, because I have no experience with a "storm jib". My first thought is, what are your telltales telling you? If you have three sets, and maybe even some leach tales you should be able to dial it in.

Because you are not using a sail that is cut like a storm jib with a high foot, and it's not set up as it was designed to be used, that is with a slight overlapping of the main, you really have to dial this in by experimentation. Because there is no overlap of your sails, they are not acting as a single airfoil. This means that you likely can sheet the jib to the centerline of the boat in moderate air such as you are sailing in. You then would balance it with how much back winding of the main you get. When you separate the sails so that they don't act as a single airfoil you lose pointing ability and efficiency, especially that of the jib. You are most likely getting an increased leeway angle, as well.

Another thought would be to cutter rig it. If you had a separate halyard and deck attachment for the tack you could bring the clue back to where you could use your standard sheets and Barber hauler. This would increase the efficiency and forward driving force of the jib.

What wind speed are you planning to use your "storm jib" and double reefing in? As the wind speed picks up above design wind speed of the boat, there is always an increase in both leeway and heading angles. This is especially true as the water becomes more choppy.
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Re: Storm jib

Postby GreenLake » Mon May 06, 2013 11:39 am

For 8-12 knots apparent wind (as measured by your wind gauge while sailing) there should be no need for a smaller jib, so I take it, this was just a test sail. However, 60 degrees doesn't sound right. The leeway etc. shouldn't be worse than with a normal sail, because the increase in side slippage at higher winds should be because of higher sail forces (overwhelming the lateral resistance, or lift, provided by hull and foils). With a smaller sail, these should be less, unless the sail imbalances the boat to such a degree that you need large rudder angles.

Did you get reasonable weather helm or did the lack of sail area in front mean that the DS was constantly trying to round up?

@K.C., I thought the purpose of the high foot on a storm jib (on a big boat) might partially be in keeping it out of the water. It would also bring the center of effort up, but I can't immediately see a good rationale for that, as it would increase heeling. Maybe I'm missing something.
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Re: Storm jib

Postby K.C. Walker » Mon May 06, 2013 12:45 pm

Green Lake,

My reasoning for a storm jib with a high foot, designed for a DaySailer, is you would use the standard sheeting location, instead of having to relocate forward. Of course, they are also more out of the water when used in storm conditions. You wouldn't necessarily need a longer luff, so the center of effort wouldn't necessarily be that much higher.

I don't know what the design wind is for a DaySailer but I would suspect that it's about 12 kn. So, a well sailed DaySailer with a crew of two, in smooth water, should be at its optimum pointing ability and it's best VMG to wind at about 12 kn. Above that we have to de-power the rig, therefore increasing the drag to power ratio and therefore increased leeway.

The smaller sail separated from the main becomes less efficient and needs to be sheeted at a tighter angle to not get back winded because it does not have the main to help its flow (relatively more side force compared to driving force). However, I suspect that a higher heading angle with a tighter sheeting angle on the small jib won't necessarily get a better VMG due to increased leeway. I suspect that sailing wider angles hotter would provide a similar VMG, if not better.

So, I'm not sure whether 60° is necessarily that bad for that set up, or for that matter any storm jib. In storm conditions you're not trying to point, you're trying to survive. Or in this case, get out in high winds that you wouldn't be able to sail in otherwise and have fun.

Again, I don't have any experience using a storm jib, so this is just thinking out loud about how I understand sailing theory.
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Re: Storm jib

Postby jeadstx » Mon May 06, 2013 2:53 pm

I made a series of drawings comparing several small boat jibs to the Day Sailer jib. I used a couple sails mention in this thread and some small O'Day boats.
Image
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John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
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Re: Storm jib

Postby GreenLake » Mon May 06, 2013 3:34 pm

John,

nice graphics. From these, the source of the problem seems clear. One reason that storm jibs have the high foot appears to be the attempt to get the clew in a position that's a reasonable extension of the jibsheet, without requiring radically different fairlead positions.

Just mentally "hoist" all these other jibs to the top, so the heads are at the same position, instead of aligning them them at the tack as in your drawings. What you see that some clews will be positioned on an extension of the line from the jib fairlead to the original DS jib clew position. I suspect that these sails would be usable with the original jib sheets. The JY15 looks like it's the odd one out. It is so tall and narrow that it's not possible to position it, which is what @Talbot found out.

However, that does not explain why he's been unable to rig it with the new fairleads that he added. I forgot whether he hoisted it as high as it will go; there may be some play there to get a better sheet angle (although that would depend on wind, 8-12kts may not let you fine tune this setup if you want to use it above 20).

+1 on K.C.s suggestion to put tell-tales on it to get a better idea what the sail is doing. (At the minimum, two sets about a foot in from the luff.)

I'm not really convinced that a small gap makes the two sails act fully independent of each other. Hoisting the JY15 higher would also reduce the gap. I could imagine that the main wants to be trimmed differently than for a DS jib.
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Re: Storm jib

Postby K.C. Walker » Mon May 06, 2013 8:47 pm

John,

This paints a really good picture. Well done.

Okay, now I'm going to have to retract my thoughts regarding the two sails acting independently, because there really is no gap. I was envisioning the sail as smaller.
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Re: Storm jib

Postby jeadstx » Tue May 07, 2013 1:42 pm

If it would help, I could move the smaller sails up to get an idea of the relationship to the DS jib.

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
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Re: Storm jib

Postby jeadstx » Tue May 07, 2013 4:32 pm

Thought I would show the jibs in two different positions.
Image
Image
Image
Image
Image
Image

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
jeadstx
 
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