Single versus tandem axles

Another post was asking about single verses tandem axle trailers, and everyone was saying go for the tandem because of safety. A couple points I'd like to make, and ask for input about.

Towing my friends double axle trailer verses my single axle, his seems to track a lot better on the freeway. Like mine always feels like it's weaving a teeny bit. Is this an effect of the extra set of wheels (or could it just be that he's got a different boat, truck, etc...)?

One possibly (depending on your situation) huge advantage of a single axle trailer is that it's much easier to move by hand. I park my boat on the stret and there isn't always much room, so I'll often sort of parallel park my boat: back up at a steep angle, so the wheel is agasint the curb but the tongue is way out in the street, then unhitch the trailer, and pivot it in by hand. This is really, really easy for me to do. I can park my boat in a space basically the size of the boat, and do it quickly. On the other hand, my friend's boat/trailer is a bith, even for the two or three of us to move by hand (to fit in his garage you've got to get it just right). We can move it in a straight line easily, but to turn it in place is really, really tough. So if you need to park your boat in tight places this is definitely something to think about (or is there some secret to swinging a tandem axle trailer by hand)?