Hi John,
The blokart rigs have 3 mast sections for a 2 m sail, 4 for a 3 m etc.

The 4m sail has 5 mast sections which are 820 mm each long therefore mast length is 4.1 m.

Luff length is debatable due to the construction of the lower part of the sail (see photo) but for all intents and purposes can be regarded as 4.1 m. The mast sock comes to the boom only but the tack is within 50 mm or so of the bottom of the mast.

Not sure exactly on the 5.5 sails and mast as I do not have one. The sail sizes are nominal only and not exactly 2, 3, 4 and 5.5 square metres exactly I believe.

Hope this helps. There are more blokart pics in my gallery. Just click on my profile and you will be able to view them.