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Ridge soaring is fairly straight forward. Most books on soaring will cover it well enough. I suggest G Dales "The Soaring Engine".
In the Southern Alps we are rarely purely ridge soaring. The terrain is complex and we often have large ridges upwind of us. There are pronounced valley breezes, sometimes just at low level.
If there is enough wind to make the ridge work, there is enough wind to make the wave work. The wave is likely to be larger and more powerful than the ridge, so if you are under the wave lift, the ridge will work great, but under the wave sink it may not work at all. When the wave is marked with cloud you can anticipate the interference, but on a blue day it can be very challenging.
If the ridge should be working, but it isn't, fly away.
If the ridge isn't working, there is a reason. If that reason is the wave dumping, fly upwind to get out of the dump and into the lift. There may be a huge thermal triggering in the valley and pulling all the energy from the ridge. Fly upwind to find the thermal. If there is a strong convergence offset from the ridge, fly away from the ridge.
The large valleys that have their heads on the Divide are prone to have cool dense air from the West Coast pushed over the Divide into the head of the valley. This then drains out down the valley. It can lead to a situation where the westerly is blowing across the tops providing reliable ridge lift, but if you drop down a few hundred feet crossing a gap you fall into the down valley northerly. No ridge lift because it is blowing along the ridge, and no thermal lift because the down valley wind is cool stable marine air from the West Coast.
When running onto a ridge use the same safe speed to fly formula as for thermalling beside terrain. Start with the target thermalling speed, add five knots for being close to terrain, add five knots if it is turbulent, plus half the windspeed. Once established, it may be Ok to pull in those safety margins if things are smooth and weak, but if the ridge is working you're probably going to speed up to run the ridge.
Always have adequate clearance. Not just where you are, but where you are going. Allow for unexpected sink. Allow for wind drift. Always stay upwind of the ridge crest. The best lift is upwind of the crest and if you drift back over the crest you will start to descend and have to push upwind to escape. The terrain may get in the way.
At any time, but particularly on unstable days, be ready for a thermal triggering from the base of the ridge breaking away and going up beside the ridge rather than up the ridge face. These will lift your upwind wing and roll you into the ridge. Always fly the feel of the glider. Don't wait until you can see the change in attitude, push back when you feel the glider moving.
These 'rogue' thermals are most likely on a weak ridge day when you are most likely to be slow and close to terrain. Be careful.
When we're heading west from Omarama we are often crossing ridges from the lee side. To do this, unless you are well clear of the ridge top and aren't going to be affected by the ridge, you need to pick your path carefully. Do not approach the ridge perpendicular to the ridge, and do not head for the low point. The wind will likely be strongest through the low pass, and the sink also.
Set your safe speed to fly and maintain it. Approach over a spur leading to a high point, turn across to fly along the ridge over the lower saddle, roll through once you see you have clearance.
Attacking the low point directly puts you in the strongest wind and sink. In the middle of any gulley so you have to turn 180° to retreat if you don't have clearance and have terrain on either side.
Attacking up a spur and turning across means you only have to turn 90° if the crossing is going to fail, and you have the whole gulley to turn in, not just half.
Often, going up a spur will be surprisingly bouyant. Sometimes you will even climb and can sail straight over the high point when you get to it. Thermals and convergence are sometimes triggered off these spurs in the lee of the ridge.
On days where there is a gentle breeze onto the ridge and the day is unstable we can get an anabatic flow up the ridges with the wind and sun on them. This allows you to float along the sunny faces just like ridge soaring. Often you need to be high to be in the good lift, so be cautious until you are on the tops.
Keep a close eye on the wind on the valley floor. If the low level down valley wind picks up it will cut the thermals off from the valley floor.
Briefing prepared by Phil Plane.
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