First, let go completely of the self-evaluation. Judging whether you’re good or bad at it is horribly counter-productive and irrelevant anyway.
The busy-ness of your brain is not the enemy here. Meditation is about learning to direct attention. What’s currently happening is that your attention is constantly being drawn away from the task you’ve given it and instead drifts over to all the random crap your brain naturally generates. The key is not to suppress all the mental “noise” (that never works), but to discover that you can simply ignore it. You can, whether you realize it or not yet, learn to just let all that noise happen in the background while keeping your attention steadily fixed on your meditative task. But if you see the noise as an annoyance and struggle against it, it will inevitably become the focus of your attention.
So, as you’re doing your task (the boat, or counting breaths), your brain will start throwing random thoughts out there. Don’t react to this, neither pushing or moving toward it to see what it’s about. Just be aware that this has happened, and keep doing the task. Deprived of your attention, the thought will simply go away. If you stop to examine it though, it will chain into another thought, and another, and so on. “Being free of thoughts” doesn’t mean the thoughts don’t happen; it simply means that we’re free from their compelling power over our attention.
Eventually, all the brain’s sputterings will fade into the background and become a kind of innocuous “white noise”, but don’t set that as a goal; just let it happen when it happens. Goals are nasty traps for the meditator. Just patiently apply your effort to the task, correct your course when the attention slips (as it will frequently) and see what happens. Progress will take care of itself. The less attention you pay to “how you’re doing”, the better.
Remember that you’re breaking life-long mental habits here, and that doesn’t happen overnight. We tend to live inside our heads, the realm of thoughts, and meditation moves attention out from its closet in your skull and down into the body (at least, that’s what breath practices do; I’m not so sure about your “boat” thing).