Velcro strap is a main clew hold down. It's intended to allow the main clew to slide lengthways along the boom, as Sail is flattened by outhaul or reefs. While keeping clew snug to the boom.
Common nowadays on many boats from Lasers upwards.
My BC 26 has one.
It needs to be snug, but not too tight...rig around boom, thru clew ring.
You will need a kicker, and a cunningham too.
My kicker now at 12.1, so as to allow one handed operation, no winching.
Not sure about outhaul purchases, but mine needs a winch in heavy winds
Dig about on here for photos of other boats setups?
BTW...welcome!
Which BC 26 are we talking about? New? Used?