Reefed Sail related to loss of pointing up wind?

I think we are in basic agreement here Jerry, that if the boat is showing weather helm and the sail is on the point of luffing, it's time to reef. I differ from you a bit in that I've found it better to use the telltales to optimise sail trim and that seems to entail being a bit more sheeted in than being on the point of luffing.

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In addition to the point about the asymmetry of the mast's shape when the sail is reefed, it is also true that reefing the sail changes its shape. The full sail has a good deal more draft than the the sail after it is reefed, even a little bit. This means that the reefed sail will have less power and therefore will generate less weather helm. The other thing that happens when the sail is reefed is that the center of lateral effort changes when the sail is reefed. This also has an impact on the sail's ability to point. As the sail's center of effort moves forward, it wants to push to bow to leeward, reducing pointing ability. Also, a reefed sail that is sheeted flat isn't as efficient a lifting foil as an unreefed sail because it doesn't have as good a shape as the unreefed sail. That also means it can't point as high. Ideally, the infinitely variable nature of the roller reefing system will allow you to balance the amount of sail to the amount of wind and the sea state. You may not be pointing as high as you can in flat water and moderate wind, but the helm effort will be tolerable and you will be comfortable that you aren't going to come to grief.

The other thing that may be impacting pointing ability is whether or not the drives are in. If they are in and in the vertical position there is both drag and competition between the drives as a point of lateral resistance and the center board. I would expect the TI to point significantly higher with the drives out, especially in higher wind conditions.

PBurling

Scott,

That is my understanding but to be honest I haven't measured them.

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Jerry D.
St. Johns, Florida
2010 TI
2008 AI

I've been meaning to offer some diagrams to illustrate sailing characteristics, as it's an intriguing subject that fascinates me. Finally got around to thumbing through 700+ pages of the "Bible"* to find a pic. This post specifically addresses: is an Island 'better' or 'worse' on one tack or another whilst reefed.



This illustration (p337) is actually comparing different mast sections/sail leading edge position, examining the L/D ratio (Lift versus Drag) using a wind tunnel. However, when the Island sail is furled partially (and only then), it presents a profile very similar to (A) when on a port tack, and (C) when on a starboard tack (although you need to mentally flip that pic to relate it to the AI/TI).

In both cases, ignore the mast profile, and substitute the round profile of the AI/TI furled mast, as it's not much different in terms of airflow.

The results:
A : L/D = 6.7
B : L/D = 8.0
C : L/D = 9.9

From this we can see that C (our starboard tack) is some 40% improvement over A (port tack). This is because profile C has the least 'reversed flow vortex' on the low-pressure (leeward) side of the sail, and it is this side that creates the lift that drives the boat.

So, for a furled sail, without changing the degree of reefing, we should expect the AI/TI to perform better on a starboard tack.

There is much more to this subject of course... as time permits, I'll try to illustrate some other very significant factors.

Incidentally, an unfurled sleeved AI/TI sail is actually very efficient in terms of mast turbulence; my guess is that it would be midway between B and C on either tack!

* CA Marchaj Aero-Hydrodynamics of Sailing

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Cheers, Max ● TI: the "Yella Terra" ● Website: www.MadYakker.com ● YouTube: madyakkermax

Max,

I think this is the key!, excellent post and diagrams! Another AI sailor was commenting that on port tacks I kept pointing lower than he thought I should. I believe his sail was not furled and mine was furled almost to the tell tales. This matches your description above perfectly. I was being more conservative because I knew I had recently been in some big gusts. It seemed every few minutes the wind would gust hard enough to turn the boat to windward and drive the leeward ama deep with full sail. I guess my friend just plowed thru those gusts and then continued on with full sail on a better upwind tack. I'm glad to know this all makes sense now. This will help in the future for planning trips. When I'm planning backup locations for worst case scenarios in heavy winds I know I can plan on starboard tacks having better upwind angles!

Great thread and glad we have lots of great sailors on here! What a fun and interesting boat.

JG, did you have the drive in or out when all this was happening?

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Drive in, fins pointed down, not against the hull

JG, it's a fascinating subject, isn't it!

Depending on the strength, duration and frequency of gusts, you could consider not reefing, if unreefed is OK between gusts. When a gust hits, ease off the mainsheet a bit to depower the rig and reduce weather helm. This will luff the leading edge of the sail, and produce a profile like (A), only a bit more exaggerated.

In an ideal world, you'd reef in at every gust, and unreef as soon as it passes, but that's not practical, so luffing a bit is an alternative.

If you have to luff the sail a lot, or still getting a lot of weather helm, or the gusts are lasting a fair time (etc), then it's time to reef regardless.

The above all relates to sailing close-hauled. As you ease off the wind in a broad reach or run, you should be able to unfurl partially or fully, and still have control.

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Cheers, Max ● TI: the "Yella Terra" ● Website: www.MadYakker.com ● YouTube: madyakkermax

During gusts I was depowering the sail a lot and still getting too much weather helm. Seems they were lasting 30s or more. So I just reefed down

Geez Max, thanks for bringing math into the equation! I will have to stick to anecdotal data.

It was a really tricky day with the wind -and the various points of land we were sailing near.

Jolly, FWIW, several times I also noticed a pronounced luffing at the top batten even as the lower sail was being slammed. So there was some gradation of wind just 15' from the water's surface. Within 2 miles of shore, It was often variable and had a twisting or swirling quality. Good luck choosing just one sail trim in those conditions! There probably was none.

Here's a wind graph of the day


You can see how shifty/crazy it got in the afternoon. Even went from calm to gale force a couple times. I reefed down to 1/2 at one point and still needed to crawl on the tramps to keep from being lifted on a reach. Wind chop hit straight from the side.

All I could think about then was, "Bungees, don't fail me now!"

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The Wind Is Your Friend...

NOHUHU... don't worry mate, maths and theory are no substitute for real world observations! Totally agree with "there probably was none [just one sail trim]". Small craft like these are very susceptible to any wind changes. If you watch dinghy or Aussie 18' skiff racing, you can see the crew endlessly adjusting sail trim etc.

JG, quite right, if you're still being overpowered whilst luffing during gusts, it's definitely time for a reef. If you're mad keen, you can reef as you see the gusts approach (by watching the water surface), and unfurl again when past, but its not easy to do with the pressure on the sail/mast - hard work!

Its challenging and fun to try to sail the Islands at max. speed!

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Cheers, Max ● TI: the "Yella Terra" ● Website: www.MadYakker.com ● YouTube: madyakkermax

Max, your illustration explains my experiences very well. Thanks for posting!

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skua

You're welcome Skua! I'm working on an article: "Sailing Characteristics of the Islands", but have a way to go yet... especially need to get good diagrams together, and I also need to consult some of our "old salts" in these forums for their real world experiences.

Have a feeling this could be a hot topic!

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Cheers, Max ● TI: the "Yella Terra" ● Website: www.MadYakker.com ● YouTube: madyakkermax