I have had  a number of requests for information on either mega venting a 1.5 sail or building from scratch
so I have put some info here, it is not a build plan, more general information on dimensions etc.

The question most often asked is where the 7mm mesh can be obtained, it is sold as Butterfly Mesh by horticultural suppliers such as:
 or...  http://www.wmjames.co.uk/butterfly-netting_2.htm

The black polyethylene netting has stood the test of time and handled quite a lot of abuse.
The areas within the blue dotted lines represent effective meshed area and are a starting point for producing the paper templates used when cutting  mesh panels.
 The templates are dimensioned  from the sail when marked out and need 12mm added to all edges for creating a bound edge to the panels before they are attached to the sail.
If meshing a factory sail it will likely be deeper in the centre (A ) than those purpose built, the mesh panels should still follow the lower edge and will be wider at point B.
Paper patterns are cut to fit inside the sail perimeter hem with a couple of mm clearance.
The mesh panels are edge bound with ripstop, fabric is cut into 30mm wide strips then centre folded before sewing, it is important to ensure the panels remain flat during and after machining, warped panels cause misshapen sails.
This video is of a Mega vent being flown in winds gusting to 32mph, the camera is on a small tripod just above ground level, strong gusts caused the camera vibration.