We had Fairwinds in Balvicar for two months before we went out though Cuan - very scary, but like most entries in pilot books the bark is worse than the bite. We have now sailed through at full Spring ebb making a cup of tea and whistling nonchalantly.
Have also had the engine fail to start just as we got sucked in from the W. end - I wasn't too worried as we had 10 - 12 knots of wind on the beam. Then - no wind except the apparent wind caused by the six knot tide sucking us through - twisting and turning to use this to keep some drive on the boat while the eddies threatened to sweep us onto the (very adjacent) shore. We made it though and sailed onto our mooring, but there were a few tense moments.
There is usually a wind shadow in the middle of the sound, and lots of eddies - so make sure you have the engine on tickover or definitely ready to start even if there is lots of wind outside.
The pilot warns about the tide sweeping you onto the Cleit, and there is some truth in this - but you need to go fairly close to the Cleit (say 3-4 boat lengths away) as it is very shallow in mid channel and further over. Not too close though as the reef extends about 10m from the perch. If you swing close to the Cleit when at about half tide Springs you may see an actual waterfall - a 12" vertical difference in height, quite spectacular.
Approaching from the West don't get too close to the Seil side on the approach - there are rocks there. A due W. approach to the middle of hte sound is safest if you don't know the water. Keep a firm grip on the helm - lots of big eddies. (He's a blimey, Big Eddy). Head for the Cleit, alter in plenty of time and swing past. Ig going down to Melfort / Craobh / Crinan then either stay within half a cable or less of the top of Torsa or come two cables or more off the top end - there's a rock that lots of people have hit. If heading up to Balvicar mid channel is fine. Lok out for pot buoys - Ihave sometimes seen one between the Cleit and the top of Torsa dragged right underwater by the tide.
The tide in Cuan runs at maximum speed soon after it turns, with very little slack water - it turns a bit more than 1 hour before HW / LW Oban at Springs and nearer two hours before HW / LW Oban at neaps (all approx and slightly variable with weather). Up to 8 knots at Springs, typically 6. Even at neaps if you miss the tide it's a struggle to get through in a small boat - at Springs don't even think about it. If you are early you can always anchor in Easdale Sound - that's another fun place to sail through.
Swing up to Balvicar and see us if you are coming through, e-mail me and I'll give you our phone no.
Information in this post should not be used for navigation