Annie has been using a ratchet block for some time as her “mature arms” get tired hanging on to the main sheet all the way up to Corio Bay in a big blow. I’ve given it a go too because I know how she feels.
And they work. Here is a photo of the block showing how the Dyneema wire slips off so you can attach it to the saddle on the mast base. No shackles needed.
Blokart Ratchet Block
It’s a Ronstan Orbit 40 block.
More about them on the Ronstan web site.
And yes, they are legal Under International Blokart Racing Association Rules. B.10.6
Ratchet Block Blokart Rules