First, your boat probably has 2 - 30A boat side receptacles, unless you purchased a boat w/o A/C.
1 will be for the house and the other for the A/C.
In my experiences you can't plug a 30A cord into a 50A receptacle or vice versa so I'm not sure where that came from with the breaker issues. Maybe I read that wrong.
Second, it's a good idea to carry a 30 to 50 adapter like this (
https://www.defender.com/product.jsp?path=-1|328|2290035|2290037&id=600990). The reason for that is because there are getting to be more & more 50A setups at the marinas.
This would enable you to connect the 2 30A cords that you have to a single 50A receptacle. I often don't bother to hook up the A/C if I'm not going to use it but still use the Y.
IF you are planning on traveling then you might need other adapters as well. I once had to connect to a 15A socket on a dock and needed the adapter to connect my 30A cords to a 15A receptacle.
IF your cords are in bad shape and you think that the boat side receptacles could be updated you might want to consider this (
https://www.defender.com/search.html?q=SmartPlug). I think that they find most boat fires are electrical in nature. One of the 1st things I did on our boat where we purchased her in '10 was to upgrade to SmartPlug.
BTW, the only reasons to use 50A is that 1) 50A is all that is available or 2) it is a lesser cost for the 30A.
Hope this helps.