Small single phase motors are not always satisfactory as induction generators.
Try spinning it at its rated speed or a bit higher and keep adding capacitance across its run winding. If you get to 120uf and it still hasn't excited you are probably out of luck.
If it does excite, use the smallest capacitor that makes it excite at about 10% below rated speed.
You will not have a very wide speed range over which it will operate, it will be very inefficient on light load and not particularly good on full load.
To make it submersible that is a major project and pigs may fly first.
Flux