I've learned that just because aluminum is relatively soft, that doesn't make it easy to drill and tap holes. In fact, its softness has its own hazards. I managed to break a tap.
What is happening is the soft aluminum shavings are getting stuck in the flutes of the tap, clogging it up. If the resistance suddenly increases, you need to reverse it, pull it out, and clean the tap. One time the aluminum shavings were stuck so hard I was wondering if they were welded in, and I had trouble removing them.
The same sometimes applies to just drilling the aluminum. If the shavings stop coming out, usually in a long spiral string, its probably because the aluminum is stuck to the bit.
You definitely need to go slow (despite it being called a "high speed tap") and make sure you aren't putting any lateral force on it.
I am making my own hydrofoil fuselage from a 1" x 1" bar. I cut the ends into a more streamlined shape with a cutting wheel, and did some additional shaping on a belt sander. I plan to continue shaping it, working on it now and then when I'm not riding it.