ok, i thinks i've got it now

while searching for pics with google the best 1 came from this site! but i couldn't find the actual thread it was from

anyway, i've pinched the diagram, added some text and attached it to this post

correct me if i'm wrong

when looking at a section of a teardrop mast a circle drawn to touch both sides at it's widest will also touch the leading edge. the trailing edge will generally be an extra 1-3 circle radius out from the circle

when looking at a section of a wing mast a circle drawn to touch both sides at the widest will not touch the leading edge, which generally will be further forward of the circle by about a radius. the trailing edge will be at least 2 or 3 circle radii further out

as the leading edge of a wingmast is "sharper" it's working range of angles to apparent wind is quite narrow, but it works very well within that range so mast rotation adjustment is very important

the blunter teardrop mast isn't as aerodynamically efficient as the wingmast but has a greater working range of angles to the apparent wind, making perfect mast rotation less important.