Here's a picture of hooking up a 1 wire Delco

If you can count you'll say "but there are 2 wires" 

They don't count the ground wire for some reason. You don't really need the ground wire because the case is grounded to the engine through the mounting bolts and a lot of people don't use it but it's pretty easy to put it on.

Hooking up a 3 wire Delco (with 4 wires counting the ground)

Same Black ground wire hookup and Orange output wire hookup

The Red wire is the sensing wire for the internal regulator and in your situation hooking it to the output terminal works well.

The black wire next to it that's hooked to the green wire is the 12 volt excitation for the alternator. The Green wire color is just because that's what I pulled out of the drawer 

The 1 wire alternator is "self exciting". When you start the engine and rev it to a little over 1000 rpm's, the alternator is now excited and starts charging.Once it's charging, it will keep charging till you turn the engine off. Then on the next start, you rev it to 1000 or so and it's charging again. You can come down to idle speed and it'll keep charging as long as you revved it enough to excite itself.

The 3 wire needs 12 volts from a keyed ignition source to make it's regulator start charging. No revving it up is necessary.

The 3 wire can sense system voltage anywhere in the electrical system depending on where you hook the wire to.

In your case with a boat that doesn't have any big electrical loads, sensing right at the output terminal works well.

And.......since any of these alternators are a lot more powerful than your original the easiest way to protect your boat wiring which won't really handle much more than the original alternator's 37 or 40 or so amps is to put a 40 amp fuse right at the alternator output.

You won't use all the amps the alternator can put out if you get a 100 amp alternator, you're basically limiting it to 40 amps.

Some people just slap on a 100 or more amp alternator with no fuse at the output and can under the right circumstances melt wiring, make all kinda' sparks under the engine box and that's never a good thing

Here's a picture of a fuse setup that would work. The wiring to the fuse should be at least as big as the 10 gauge alternator output wire.

If you want to use all 100 or so amps, then to be protected you'd need some larger wiring all the way from the alternator to the ammeter in the dash and back to the engine again and you'd need the same size ground wiring.

The simplest but still effective setup would be the 1 wire alternator with a 40 amp fuse on it's output and the rest of your boat wiring could handle that.

Like with most things in life, there's more than one way to do do it, so maybe you'll get some other opinions.