Thanks for your input. I have been talking to some rigging guys, and have found that vang angles need to be between 30 and 45 degrees. From this I can determine how far I have to lift my mizzen boom to achieve a 30 degree angle. However my knowledge of vangs is limited. It is a big learning curve for me. Through Pythagerus maths, I know what height I have to raise my boom, however I still have to find out whether the mizzen mast can support a vang a couple of meters from the base.