I have a teen boy. And a pre-teen girl.
From the 2 examples you gave, I would say you are too all over him. Why does he ignore you? Not because he is intentionally being defiant perhaps, but maybe because he doesn't see the "why" behind it. One of the responses you already have asked about his snacking before dinner affecting his appetite at dinner. Does it? My teen son can eat a couple of snacks in the 45 minutes before we sit down at the table and STILL eat a full healthy dinner. They are growing so much at this age, that unless he is overweight (and I don't mean that little pudge they get just before they shoot up in height---and around age 11-13 they can get a belly/waist they have never had before on even the healthiest, trimmest kid)... then there isn't a real reason to restrict his intake. Unless you just like setting arbitrary rules.
If he is "starving" and "can't" wait until dinner, but then doesn't eat his dinner after snacking, do what you would for a younger child. OFFER him a snack, but earlier, so that he has time to be hungry for dinner. My son comes home from school absolutely famished some days. He eats for 30 minutes non-stop when he first gets home. Does your son have a snack earlier in the afternoon (after lunch, before dinner)?
As for the boat. Well, I am not on scene so it is hard to say, but why fuss at him? He knows. He also knows (or thinks he knows) his abilities and limits. Let him test them out with you right there if he messes up. He is wearing a life jacket. Are there piranha in the water or something? What do you think will happen if he does fall in? Sure, he could hit his head. But more than likely he will just get wet and embarrassed, and learn that it is a bad idea to stand there and will quit, which is what you want, after all.
If you fuss over everything, he will tune out whatever you say when you fuss. So stop fussing over everything, and let some stuff go (or quit fussing and start acting on the first time, instead of warning him for things he should already know).
My son snuck out of his cabin (with one of the pastors' sons) while at camp this past week. They got caught. And had to do jumping jacks or something silly that embarrassed them and was annoying. There is no need for me to follow up NOW and say-- you shouldn't have been doing that. He knows! So I laughed at him. HAHAHAHHAA You got caught! And had to do jumping jacks! HAHAHAHAHA
His sister had cabin mates that snuck out too. She stayed where she was supposed to. They got caught, too. She heard them getting into trouble. (Pat on the back for you, sweetheart. Aren't you glad you did the right thing?)
Give him a little room to grow up. My son gets his learner's permit this week. Scary? You betcha. But being responsible for himself is what growing up is all about. We have been grooming him for self-responsibility his whole life. How can he practice it if we stand over him and constantly point out every single danger and foible he could get into? It doesn't work that way.
So yeah... he probably listens to Dad better, because Dad ignores (or just doesn't see, as some men are known to not see certain things) some of the more minor piles of poo your son might step in, and is confident that your son will learn from his mistakes. You can't learn from them if you are never allowed to make them. When Dad DOES say something, your son listens. Fewer words are listened to more carefully.
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Oh... just wanted to clarify. By pre-teen, I'm assuming you mean an 11 or 12 year old. I was talking with a friend earlier this week who mentioned another mutual friend had referred to her daughter as a "tween". Her daughter is 6 years old. Ummmm... NOT a tween. Not even close. Tween is double digits, right? Anyhoo... just wanted to clarify that we aren't talking about a 9 year old.