[ardoin]

This is a first for me. With the temps warming I took her out this morning on the Chesapeake Bay. On the way out the instruments showed the wind from the South. So once I got out a bit I cut the engine down and pointed her to the wind and began to raise the sails. But the wind in the sails was NE instead of S. This was confusing for a while. After a couple of minutes I decide to sail with the wind I felt on my face rather than what was shown at the instruments. Went out NNE for a while and as I got further from land the wind shifted more to E or ESE but the top of the mast still showed the wind from the South. After about 2 hours it all went back to normal and the wind was SSW.
I imagine this was cause by the temperature inversion cause by the very cold water and the warm land, but it was the first time I've encountered a case where the wind at 60ft up the top of the mast was completely different that the wind on the deck and the sails.
Learn something new every time I sail. Guess that's why my house floats.

 

[JohnRPollard]

Could it have been an issue of the instruments hanging up/sticking at the top of the mast, after the long winter lay-up? And then after sailing a while the windvane loosened up and began to show the correct wind direction?

 

[AdamLein]

Where you sailing near any bridges or cliffs or other landforms that could change the course of the wind or create eddies in the air? Close to land you'd also expect different wind at different heights (why sloops are so tall). That would explain why it changed as you got further from the land.

Also, how was the sail trim? Such a difference in the wind direction should have made it difficult if not impossible to trim the sails so that they weren't luffing at any height... maybe with lots of twist. If trimming was straightforward then I would look to instrument problems.

Also, what about signs on land? What direction were flags pointed, etc.

 

[ardoin]

John, instruments are fine. I live aboard and sail in the winter (including this saturday without problems)
Adam, there are no high land masses on the bay and i kept looking at the sail trim expecting to see the main twist, but all i saw was some strange twist in the jib, but not much. Also, the water is about 37 deg and the air temps on the bay were cool (i guess about 40 deg, i had to wear a wool cap, warm jacket and gloves). When i got back to Back Creek, the temps were in the 70's and there were really strange looking light refractions just above the horizon as that i noticed on my return to the Creek. I didn't notice them on the way out.
There was even a time when i was sailing just over 5kts on a starboard tack while the instruments showed i was heading straight into the wind.
Definitely a new and strange experience for me.
Was anyone else out in the center of the bay this morning to early afternoon?

 

[US27inKS]

The wind can do so really weird things in this part of the country as well. Last summer I was heading back in to the marina on a beam reach. Suddenly and without warning the boat jybed and I was beam reaching from the other tack. Next thing I know the sails are luffing and the wind is still coming around. I looked up to see the windex do a 360, and before it was over (about 10 seconds) I was heading in on my original tack and point of sail. Gotta love Kansas weather.

 

[twinsdad]

The phenomenon is not that strange. Ask anyone who has ever watched a football game at Giants Stadium!!!

 

[WanderingStar]

I've only experienced that close to obstructions. Sailing up a canal among trees and houses I've had the top of the main belly one way, the bottom the other. She kept sailing though. The other time was under the Brooklyn Bridge, when the boat slowly rotated several times, regardless of what I did with the tiller. The wind seemed to be coming straight down.

 

[Boasun]

Also a rapidly passing Low will cause the wind to either back or veer as it goes by. And the inversion could be adding to it also.

 

[paulk]

We had some funny wind during a race once. Coming up to the finish mark, (Take your own time passing within 75' of it when it bears 360º) doing about six knots upwind on starboard, when I notice the wind's riffles on the water stop in a zone about 100 yards away from the mark. We proceed at six knots to sail into an absolutely flat calm. We stop, lose steerage way, and get spun around by the tide several times before the current carries us back into the breeze. We gybe around, sheet in, pick up speed to six knots again... and sail back into the absolutely flat calm. This happened three times, with competitors coming up from behind and having the same thing happen to them. Finally, we decided to stay in the breeze well past the mark so that the tide would carry us towards it, instead of away from it, when we sailed out of it, and we were able to finish. Very strange.

 

[39512]

Frank Bethwaites book Performance Sailing has a lot of information regarding the differences in wind at the surface and wind aloft and some of the factors involved.

 

[Boasun]

In some areas where you will find wind eddies. Small ones could be caused by an anchored large ship. Bluffs can cause a change. Plus a fast moving Low or High can cause wind veers & backings. Then you may have a combination of any of the above. So watching the Cat's Paws on the water is a good tattle tell for one. Watching the sails of other boats around you and another way.
For an example: Saw a boat with a skinnaker set & flying...the next moment they had a spinnaker wrap around the fore stay. Which fore told a strong gust and change of direction coming our way. Yep we got knocked down. But then she righted herself. Lucky us.