If I have a flat floating object roughly 6 feet long about a foot and a half wide weighing around 9 pounds, and it had 2 underwater thrusters fixed on the bottom side of the back end of this object with each thruster having around 9 pounds of thrust, what would its top speed be or can you even figure it out with this information.

Apples and oranges.

Thrust does not have a speed component, it is force pure and simple. 9 pounds of thrust will move 9 pounds, probably very very slowly.

Let's look at an automotive example with thrust equaling torque. Torque gets you started, but horsepower determines how fast you can go and in your case you don't have a power figure, just the thrust (torque)..

Even if you could hazard a guess as to power, you don't know what the losses are.