Hi Colin,
Your question was not silly. Look at what you learned. That is very worthwhile. To windward the best we can do is have the daggerboard and rudder operating at leak lift to drag ratios. To calculate L/D, simply divide Cl by Cd at points along the drag polar. I think you will find that peak L/D occurrs at or very close to a lift coefficient value of one, Cl = 1.0. Read several points along the polar. Calculate L/D. Plot L/D vs Cl and against angle of attack. This will tell you some interesting things.
Good luck,
Bill