Going to help a friend set up an early tales derivative with an M7 raking rig.

What's the datum for bolt-upright?  is bolt-upright really bolt-upright or is it some way back.  Any length in milimetres gratefully appreciated.

Jon

Mine has an upright mark which is pretty much bolt upright. It's a running setting though and only gets used on open water.

I tend to sail with between 6 and 12 inches of rake until we're overpowered.

There have been several threads on this one over the years describing the dangle technique.  Set boat level, best technique being a spirit level to set the stem vertical.  Dangle a weight on the main halyard and measure the distance between the aft face of the mast and the string at the mast heel level (assuming deck stepped).  Upright is just that, but only for running and not in vigorous conditions.  Basic light wind setting usually 9 inches, maximum rake is anything up to 2ft 6in, making sure you can still get good rig tension and the lowers on properly, adjust lengths of string to achieve this

MROA members can read this library article (from an old magazine).

I must remember to get some colour versions of these photos (that accompany the above article). Anyone care to send some in, to make things clearer?

Does anyone in the Merlin Class use a Loss Rig Tension Meter? If so what tensions are optimum?

Generally we don't bother because tensions change as the breeze increases.  Rule of thumb is to just have the leeward shroud just tight when going upwind.

The only time i've used a tension guage is when setting the cascades up (changing the purchase) and we put the tension gauge on to make sure I could wind on enough tension with the purchase that I had.