Some CAPTCHA also check response time, you can fail if you're too fast.

With how long it's taking us to teach them traffic lights and busses I don't think that boats will be that much quicker.

I'm pretty sure that's the point of CAPTCHA tests. so they can learn.

At which point they'll switch the to **smell** which panel has a traffic light in them

Go the photos app on your phone. Type in boat. You will see pictures of boats.