2d physics for balance game like Wii Party Pirate Ship

Sorry if this is a total noob question. I'm new to physics in Unity. I have something working, I just want to know if there are other or better ways.

There's a game in Wii Party that looks like this

Here's a video of it in action. See 10:40 https://www.youtube.com/watch?v=KQPVv21G-4A#t=10m40s

You put characters on the various decks of the mast. First to tip it over loses.

What I did so far

 +--Ship [RigidBody2D + HingeJoint2D attached to nothing (world)]
 |   |
 |   +--Deck1 [BoxCollider2D]
 |   +--Deck2 [BoxCollider2D]
 |   +--Deck2 [BoxCollider2D]
 |
 +--CounterBalance [RigidBody2D + HingeJoint2D attached to Ship]

For the HingeJoint2D on the CounterBalance I set it to Use Limits true and set both the Lower Angle and Upper Angle to 0. This works mostly. If I increase the CounterBalance mass it gets harder to tip the ship. One thing that doesn't work is Ship drifts up a little when I press play. Given it's on a HingeJoint2D it seems like it shouldn't budge. No idea what I'm doing wrong there :(

Is that the best way to do this? It seemed a little strange to me to use a HingeJoint2D to add the CounterBalance. Is that the "correct" way to add a counter balance? I don't see another way to make a "rigid" connection between 2 masses (2 RigidBody2Ds).

If I move CounterBalance as a child of Ship it has no effect. DistanceJoint2D doesn't work because it's doesn't keep things rigid. It's just like a pole on a hinge.

Maybe this a really "noob" question but I didn't see anything in the tutorials. Or maybe it went over my head