would you pass to windward or leeward ....?

All other things being equal, to windward for the reasons stated but in practice it would depend on the usual range of factors such as destination, heading, point of sail, tide etc. etc. I think a lot would depend on whether it was potentially unsafe or otherwise to pass through the windfarm itself in terms of depth. Do you put yourself off a lee shore on purpose if you have the option? Not usually.
 
Hot air farm

These things are going to be so efficient you might get sucked into all the hot air surrounding 'em, according to some sources. Phew.

I would definitely give it a wide berth, especially if asked to contribute to the ''revised'', revised, newly revised building costs..

Of course when they find 'A N other' £75b to plug the cable in, your compass might go a bit doolally as you sail past..

Afaik the ones I have seen rotate pretty slowly,( and part time ), the wind shadow will be less than a passing lighthouse.
 
Go to windward

If you check out some of the papers on the wind shadow caused by wind farms, you'll see that there is a very significant wind shadow to leeward of the farm, the shadows are visible in satellite RADAR images and have been measured using airborne RADAR. You can also expect higher wind velocities and changes in wind direction around the upwind edges of the farms, because the farm acts like dam (brick wall) and the wind tries to go around the farm, accelerating around the edges.
You need to remember that a good wind turbine will take 55%+ of the energy out of the wind that goes through the blade, and a big wind farm may be exporting 75M watts or more of electrical power, so there has to be a lot less wind on the leeward side.
 
Ian_Edwards said:
.......You need to remember that a good wind turbine will take 55%+ of the energy out of the wind that goes through the blade, and a big wind farm may be exporting 75M watts or more of electrical power, so there has to be a lot less wind on the leeward side.
Click to expand...
You also need to remember that the blades are a long way above sea level and a long way above the height of the rig of an average yacht.
I have frequently passed our local wind farm (Kentish Flats, 30 turbines) to leeward and I can't honestly say I've noticed any difference at all.
I raced dinghies for 45 years and believe me I would notice any significant effect.
 
Windward?

.
Thre was a fairly recent thread on this. Apparently there is quite a lot of turbulence downwind, but how far downwind I don't know.

We have sailed less than a mile offshore/downwind from the wind turbines at Carnsore Point in 30 knots and didn't notice anything unusual.

- W
 
I'd still go upwind

The hubs of the 5M turbines on the Beatrice wind farm are 88m above sea-level. Each blade is 63m long (126m Diameter), which means the blades are 25m above HAT. My air draft is 17.5m plus the VHF ~1.5m so I have ~6m clearance, if I'm daft enough to get that close!

http://www.isprs.org/publications/related/ISRSE/html/papers/272.pdf
This paper shows that there is a significant reduction in the measured wind speed at least 15km down wind of the farm.
 
Ian_Edwards said:
The hubs of the 5M turbines on the Beatrice wind farm are 88m above sea-level. Each blade is 63m long (126m Diameter), which means the blades are 25m above HAT. My air draft is 17.5m plus the VHF ~1.5m so I have ~6m clearance, if I'm daft enough to get that close!
Click to expand...

That'd be ~6m clearance minus height of tide and swell.
 
Tide no .... swell yes

"That'd be ~6m clearance minus height of tide and swell."

The heights are to HAT, Highest Astronomic Tide, so on a normal tide you have more clearance by a meter or so .... and yes you need to add any swell, which will reduce the clearance, but the point is the turbines are not well above mast height in my book.
 
Ian_Edwards said:
"That'd be ~6m clearance minus height of tide and swell."

The heights are to HAT, Highest Astronomic Tide, so on a normal tide you have more clearance by a meter or so .... and yes you need to add any swell, which will reduce the clearance, but the point is the turbines are not well above mast height in my book.
Click to expand...

Hmmm - Have you noticed that dry feeling in the throat when you go under a bridge you are certain is well above your mast. I have and I don't think I'll try it with a bloody great blade spinning a few metres away.
 
Looks like some of them are going to cover some pretty big areas of sea. If there's enough depth I think I'd go straight though the middle; it could be a long way round.

Will they give any useful lee in bad weather I wonder?
 
Ian_Edwards said:
http://www.isprs.org/publications/related/ISRSE/html/papers/272.pdf
This paper shows that there is a significant reduction in the measured wind speed at least 15km down wind of the farm.
Click to expand...

Since the total airflow must be the same upstream and downstream, the windspeed must average out. It will be more turbulent downstream, and some airstreams will go around and over the wind farm. Normally you'd expect the air that goes over an obstruction to have r-joined the surface flow at a distance of 20-50 times the height according to most texts..

Where there is a line of turbines at an angle to the wind, there must be wind bends produced, which would influence upwind tactics.
 
Having seen the planned Irish Sea farms it will be difficult to get around them if going to the IoM from Liverpool or N Wales. I'm sure many of us will need to pass through the middle of them on a regular basis. I hope they are all clearly numbered so I can tell where I am, like on the motorway.
 
lw395 said:
Since the total airflow must be the same upstream and downstream, the windspeed must average out.
QUOTE]

Thats a bit of a non sequiter.

If it were true the whole of the Earth would have to have the same windspeed.

Where is the energy coming from if it isn't from the kinetic energy of the air.

QED Wind slower downstream !
Click to expand...
 
davidej said:
lw395 said:
Since the total airflow must be the same upstream and downstream, the windspeed must average out.
QUOTE]

Thats a bit of a non sequiter.

If it were true the whole of the Earth would have to have the same windspeed.

Where is the energy coming from if it isn't from the kinetic energy of the air.

QED Wind slower downstream !
Click to expand...

So where does all the air arriving at the upwind side, but not leaving the downwind side, go?
In fact the same mass of air leaves as arrives, and the departing air is at a lower pressure.... so the speed increases form just in front to just behind the turbine!

It's the air which goes around or over the farm which misses the boats in the lee.
Click to expand...
 
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