Why a Mid Length board for foiling? What are they?
Mid length boards are modern foil boards that are about 19” to 23” wide and longer than traditional wing foil boards (rectangular shape). The length and waterline shape of these boards give them more speed in the water with less effort. The speed of the hull allows them to take off easier with smaller hand wings or with less low end power like from parawings. They can also be used to take off with more speed for faster or smaller foils. Also these boards work well as prone foil boards for surfing especially beginners.
When should I move to a mid length board from my beginner board?
Getting up and riding in either direction should be easy in mixed conditions. You will want to have spent some time in rougher waters and easily be able to get onto foil in those conditions. Also, you should be easily riding a faster type front foil wing (mid aspect to high aspect), can comfortably jibe and are beginning to try to ride swell. The mid length board does not offer much side to side stability so the early sessions may feel a bit frustrating. Mid length boards are a great option to move to as your second board.
What volume should I pick?
Most people go right around their weight in kg to +5L for their first Mid Length type board. This volume will allow you to get out of the water quickly but not be overwhelming long when turning and carving. If you want more stability and easier take off for parawinging or light wind riding, consider a board with about 10 to 15L more than your weight (in kg).
I want to parawing eventually? How do I size this board?
I would go with the board in a volume equal to your weight in kg up to 15L higher if you are an experienced wingfoiler. Make sure in the early learning phase of parawinging to use a bigger foil as well.