Hi guys,

The standard way that we measure the mast rake over here in Aussie-Land is using one of the trapese wires taken off the bungy:
Tie a small string to the end of the dogbone and measure to the top of the hull above where the bridle attachments are. You can use your hand as well for some less acurate measurements. Hold your fingers on the string at the appropriate length where it hits the hull. Still holding at this point go to the back of the boat and measure along the top of the hull to where it touches the hull.

For sloop rigs somewhere between just in front of the back beam and the hatch cover is about right. Mine is just behind the rear beam and seems to like it there but it depends a lot on what waves you are sailing in, how deep your mains'l is cut (especially up top) and how stiff your battens are and how tight they are in (again especially up top).

Oh, BTW. Most of us over here take the mast pin out after we've stepped it to avoid exactly the problem you describe.

cheers,
ABC.