I'm setting up for 2.3m twin poles.Can anybody offer any guidance on how far aft my spinnaker sheaves should go in relation to the mast. Is it critical, or will somewhere in the middle thats convenient for string suffice? 

What about a when the sheet is acting as a guy? Do I need a method of moving the sheeting angle further forward?

I'm really hoping to only cut the holes once!

Any advice very gratefully received.

Where they were seems to suffice!

I've never seen any boats that changed their spinnaker sheaves from the original point.

The guy is often tucked under a hook of some sort by the shroud, so it is out of the crews way.

"The guy is often tucked under a hook of some sort by the shroud, so it is out of the crews way"

errrm, more like the guy needs a reaching hook near the shroud to hold the pole down, and keep the guy off the shroud. The convenience for the crew isn't really the point?

Many conventional kite boats use 'twinning lines' or 'stranglers' to pull the guy down to the gunwhale (a ring or pulley that the guy runs through, on a line running through the gunwhale and back to a cleat)
Few Merlins seem to  have this, is there any reason? It might be better than my current hook arrangement where the sheet keeps getting hooked. It also means the helm can do the changeover in a gybe. The Winder boats mostly seem to have sort of a 'button' or 'mushroom' to latch the guy under, I'm guessing that these release the sheet by default because the angle is different?
Nothing worse than both being sat out and realising the sheet is in the leeward reaching hook...
Hope that helps, sorry if I've hijacked your question.

The 'mushrooms' are a great invention as the self-release in a gybe.

The snodger/tweaker (pole downhaul) keeps the pole down. Crew can't hike out with the guy across their back! Although as wind increases crew will slide aft anyway.