Colin Bell wrote:

So, if designing for a balance of 35%, what yard angle (range) would be appropriate?

35% is rather too much balance, I feel. The sail will overbalance and snatch on, instead of feathering, when going to windward. 25% is safer, but still marginal.

Derek Van Loan specifies an angle of 125 to the luff, 35 above horizontal, and that would be the lowest angle I'd want to use for a  junk sail with maximum balance. 

(Except for special cases - split junk and my latest wingsail, for example)

Yard angle is directly related to the amount of balance (part of the sail that projects in front of the mast) a sail has. The more balance, the lower the yard angle. This is because the the attachment point for the halyard to the yard needs to fall more or less vertically under the mast head halyard block. If this is not so, the sail will not hang naturally in its required position.

I have been drawing sail plans and comparing them. Someone please educate me as to the advantages/disadvantages of yard angle. It appears to me that an advantage of a sail that is roughly a parallelogram and all of the battens are parallel would be better sheeting for the head of the sail. There must be advantages of a higher yard angle because you see it so much. It appears the halyard connection can be closer to the center of the yard, with a higher angle. Does the peaked head perform better in heavy weather as your storm sail?

Thank you for any input!