My Riva is launched today.31 ins long x 11 wide.cost approx £230 plus elbow grease.
9.2 battery 3.700. Plenty of lead fishing weights for ballast and fingers crossed.

Hi on the subject of scaling up plans i convert plans to PDF format and then print for adobe then you can up the the % and tile print
and make it any size you want hope this helps

Just had a quick look and there are some good detailed plans. You will need some software to scale up the drawings to the scale required but this is possible.

Well worth a look if you like scratch building.
Thanks for sharing