I'm all for a good project, but here's a few things I see that haven't been addressed yet.

First is that the battery listed is a 24V 20Ah pack, but the specs further down the page say 30Ah pack. So right off the bat, the battery performance specs are questionable.

The 20Ah battery would be running at absolute maximum power at around 800 watts by the time you factor in voltage sag. You may get 60lbs of thrust with that power, but only for maybe 15-20 minutes if you are lucky, as you will not get rated power out of the battery at a 2C discharge, not to mention it will shorten the battery life significantly

Your dreams of getting 150lbs will be dashed as the prop blades will not take anywhere near that load and snap off at the root. Not to mention the faster you spin a prop the less efficient it becomes.

Go to the Seabob page and take a look at how much power they require (2.2kW for a claimed 4.97MPH underwater for their slowest unit) and then try to figure out how they get an estimated 60 minutes of run time out of a 1.2kWh battery.

A little bit of simple engineering math up front will go a long way.

My recommendation would be have fun with the learning curve but don't modify the housing such that you can't at least change it back to a usable scooter when you are done.

Have fun,
Jon