Onya "sn".
and on "landyacht"'s advise, I fitted a mudguard (with the inside totally enclosed to the tandem) to keep little hands away from that wheel.
Not a great photo but you can get the idea of the 25mm x25mm x1.6mm galv RHS, tandem chassis.
It attaches to the front of the yacht by the mast step with a flat plate 3mm thick with 2x 8mm bolts about 50mm apart. So 3 bolts (2 at the front and the left hand axle retaining bolt) removed and it's back to a standard yacht in a few minutes. It slides into the standard 35mmx 35mmx2mm rear frame of the mini.
I've had a 108kg passenger in it.
Me, while I'm teaching kids to sail.
Remove the wheel and put it back onto it's standard axle and your sailing again by yourself.