[ursa minor]

This isn't a situation where the Dive is "underpowered" so much as how the power gets to the water and some basic principles of naval architecture. Also, note that even with double the power (it has 2, 300 HP Evinrude outboards now) it really wouldn't make a huge difference in speed.

As a displacement vessel, the length of the waterline dictates what the maximum practical speed will be, increasing the power above whatever is calculated to be required to produce "hull speed" will only increase the top speed a small amount even with a significant increase in power.

As has been noted in an earlier post, Diversified Contracting has a similar sized barge with twin 250 HP outboards. I've watched it go by our place many times, the operator runs those engines HARD and even with that I'd guess top speed is between 10 - 12 mph. It sounds to my ear as if the propellers cavitate a fair amount while doing so. Using Diversified's barge as an example, it looks like the Dive is similar in length and has roughly the same power so top speed would be in the same general range of 10-12 mph.

If they're not getting to 10 mph or so, I'm guessing part of the problem could be getting the propellers to convert the power available into actual thrust. The barge that APS referenced looks like it's powered by a pusher tug. If so, that likely has a diesel engine turning a much larger diameter and slower turning propeller that can get a better bite on the water to push the barge. Tough do that with engines designed for pleasure boats that turn small diameter propellers at high speed.