While my boat is in the shop I have been looking at new boats on line.  I have noticed the same thing more than once and that is that aluminum boats although lighter are slower than glass.  I even looked at boats with similar hull designs, like the Tracker Tournament aluminum and the Nitro X5, same length, same motor, the aluminum boat is lighter and 10mph slower.  I am assuming that this is due to drag, but aluminum being non-porus, not to mention painted, I wouldn't think that drag would be that much of a factor.  Can anyone explain this phenomena?

The key word here is "similar" hull design.

Because they're built in a mold,  fiberglass hulls can be tweaked and modified for speed far easier than aluminum can and still keep the cost on aluminum down.  There are some performance aluminum builders out there,  Express is one.  

I've also read somewhere that because of the weight glass plows through water rather than glide over it.  As mentioned, glass molds can be tweaked to the optimum profile.

High performance bass boats have a "pad" type hull that the boat rides on to lessen the hull contact with the water. The lesser the hull contact with the water, the faster the potential speed. It is all about drag.

To add to Wayne P.'s post, when you're up on that pad you shouldn't be plowing anything and if you push it until you chine walk, you're barely touching the water.  If your motor is below the power specs for your boat, then you could plow the water somewhat when you get up on plane because the motor isn't able to lift the bow and midships out of the water.

Most aluminum boats sold on today's market are usually under powered but there are some high performance pad hulls available such as Xpress, G3, War Eagle, Triton, and the older Tracker Avalanche. With the proper set up and horse power these boat will offer performance equal to fiberglass boats maybe not as fast as the faster glass boats but plenty enough for any speed junky.

I have a friend with an Xpress X19 with smokin' hot Evinrude E-Tec 200 H.O. on its transom turning a 28-inch-pitch Raker propeller that will hit 72.8 mph; it will make me grin.

When I posted this I was thinking in particular about this tracker boat, and the g3's Speed estimate for this boat is 10mph is less than the fiberglass with the same motors.

Those hulls are not conducive to speed  

When I posted this I was thinking in particular about this tracker boat, and the g3's Speed estimate for this boat is 10mph is less than the fiberglass with the same motors.

and the fiberglass boat package probably weighs more than the aluminum.

What that aluminum boat doesn't have is a hull that's been designed with lift components built into the hull.  Fiberglass boat manufacturers utilize air pressure built up under the hull to help lift the hull up out of the water while the engine is pushing the boat forward.  Removing wetted surface area = increased speed.  

An aluminum boat can also be designed that way but the metal fabrication costs to do so drive the costs up and thus,  push the price of the boat out of the majority of aluminum boat buyers pocketbooks.