I'm not sure what the actual angle to apparent wind is. I was thinking 25 degrees is reasonable but on the high side. Let me know if anyone has figured it out.
The easiest situation to think about it is when your board speed = the true wind speed. In that case, the apparent wind direction will be halfway between your heading and the true wind direction.
So if you are going 10 knots in 10 knots of true wind heading at 50 degrees to the true wind, then the apparent wind is at 25 degrees, halfway between true wind (0 degrees) and your heading (50 deg).
As you go faster, the apparent wind shifts more in front of you. If you want to go 10 knots in 6 knots of wind, you aren't going to point very high because the apparent wind angle will be very high.
Nico wrote:70 degrees cannot be right, or it would take you hours to tack upwind.
Thats just 20degrees better than no upwind at all.
That's true. You have to slow yourself down to point higher though. You can't point very high at all when you are riding upwind at nearly twice the wind speed.