Here's the classic. I've been using that since I started. This design is also quite easy to build. I use about 10Kg of weights. Together with a rotating disc on the ground I also use it for muscle training. Just rotate 50 times in each direction every day
Without disc its also useful to practice the handle passes for the WO's.
I measured the pull of the boat on me and found it was about 25Kg skiing straight behind the boat. More than I expected.
Which brought me to consider the next idea, still conceptual, I'm going to build it. The idea is that like this it mimics the effect of pulling - the force becomes less for a while and then snaps back to normal.
Different tricks, like SLB vs WO, will require different weights/ arm lengths..
I'm interested in any other solutions and experiences with them.