Careful use of a scotchbrite pad, used in only 1 direction, can evenly create a matte finish once you get the aluminum buffed to an even sheen.
But it all has to be pretty close to the same sheen 1st, then gently remove the polished look.
Most matte metal finishes create the look of grain on the metal. Using a scotchbrite also does that.
If thats the look you're going for, I've seen it done, and done well.
Why matte?
What boat?
Pix?