Rush 6/12 - take yer weed fins

[DimitriMilovich]

First time back to Rush in many years, outside of some ice sailing expeditions. It's still a pretty place and the meadowlarks are still there, unlike Utah Lake's west shore. Sadly, the nice clear water is just perfect for weeds. My 7.4 had almost enough wind to plane, but the 34 cm fin was harvesting all the seaweed needed to wrap sushi for a month. A little surf fin or weed fin might be OK, but big sails are out. There may have been some kite rides later.

The afternoon wasn't all wasted, as I still got to drive back with a chocolate-dipped $1 cone from the Dairy Delight in Tooele. Some things haven't changed there yet.

Have y'all heard about the proposal to put windmills on the Stockton Bar? How's that - insult to injury - the water goes, but when it starts to come back someone's thinking of snagging our wind. (sigh)

[DeanDavis]

I'm not involved in the wind farm but I have looked at some of the wind data. It looked promising with a 6.0 m/s (13.4 mph) average but a modern wind farm needs closer to 7.5 - 8.0 m/s average at hub height. Normally 6.0 m/s on a 30 ft tower would be close at hub height (60 m) due to vertical shear (wind speeds increasing with height) but not on the bar the wind had no shear. As a result I think the project is somewhat on hold. If the wind turbine costs keep coming down or if electricity prices rise the project might have a chance. If it does go through you don't have to worry about losing any wind. The hub height of the turbine is ~60 m (180 ft) and the blade are about 38 m long (114 ft) so the blade tip is still 65 ft off the ground (well above a wind surfer). Also when siting a wind farm we usually space the turbines about 8 rotor diameters downwind of each other so that the wind has time to build back to full strength before hitting the next row of turbines. So as a rule if you are ~300 m downwind of a turbine the wind is back to full strength. For me personally having some large wind turbines generating millions of kWhs while we rip on the water would only enhance the beautiful sceanery as well as the overall experience.

[DimitriMilovich]

Thanks for the informed comments, Dean. Being born in Holland, I've always liked them too. I'm still nervous about their effect on sailing though, and here's why. Although 8 rotor diameters may work for windmil siting, we may not be as happy. Windmills are happier than sailors because the effect of gusts and vortices coming into them from upwind are smaller, because the blade tips, where most of the power is generated, might often be traveling 120-150 mph, so their apparent wind isn't as affected.

I've always understood that wind quality for sailors, however, can be affected for 10 to 20 times the height of a (stationary) obstruction. Most yacht racers use a factor of 10. A classic sailing/aero manual, Sailing Theory and Practice by Marchaj cites up to 20 times the height, with, and I love this, "the reaction of the wind to the barrier varies remarkably at different distances from it causing apparently incomprehensible behavior on the part of the sails." (I've often been incomprehending when I've sailed!). Ask anyone who's sailed in Aruba how the wind quality is downwind of hotels and how far out you have to sail for clear air.

Anyway, if you now look at an average max height of 180 feet plus the 114 ft blade, you're now at almost 300 feet high. 20 times that height and you're over a mile where some effects can be felt. Now add in the possibility that you will have vortices coming off of 150 mph blade tips which can travel some distance and who knows what the quality of the wind will be like. I hope this is all Nellie nervousness on my part, but it would be nice to know the answers before it happens. Ponds trip anyone?

[DeanDavis]

Dimitri,

I think you point about distance being different for turbine siting and sailing is well taken. 8 rotor diameters is far enough for the wind to regain its original energy content but the quality of the wind may be changed. My guess is the quality would not be dramatically different and I only say this because we don't use different turbulence factors (and I have never heard of any such factors) for second row turbines. The other thing that should make you feel better is that the lake (where we sail) is actually about 1.25 miles from the bar which is about 30 rotor diameters (much much further than the minimum of 8).

Your Aruba example is an interesting one but very different than a wind turbine in my opinion. The wind has to move around a large building while the wind flows through a wind turbine. At best a wind turbine extracts about 45% of the available energy in the wind and lets the rest past through (picture the hotel as a net not a building). If you try and slow the wind more you get less efficient. I can also see how a tall building is worst since it makes a bigger hole behind it. But putting a wind turbine on a taller tower does not have the same effect so the height equation would work differently. Just as an example if a wind turbine were placed on a very tall tower (lets say 1000') I think that would ultimatly make for less ground influence than if it were on a very short tower. This is the opposite of the building example because the tower is a trivial portion of a wind turbine's influence on the wind (i.e. put the hotel on a thin pole). A hotel on a thin tall pole is taller but is it worst for the wind surfer? If the pole is high enough I think the hotel is no longer a factor. The bar is like a taller tower (an additional 230 ft) which means less ground influence not more influence further away (unlike the 10 to 20 times the height analysis).

I have a very very hard time thinking that at these distance the wind turbines will have any influence on the lake winds but if you are still concerned then I would guess the Northern Europeans are the ones to ask. Some regions of Northern Europe are now producing 30-50% of their electrical consumption with wind power and much of these would be on the coast lines where wind surfering would be popular. From pictures I have seen the turbines would be closer to the water (often right behind a small beach) than what we find at Rush. If they aren't complaining loudly then I think it must not be a problem.