Hey author, whirlpools dont form from ships sinking they form due to two or more strong currents meeting at the same point much like tornadoes form from multiple strong air currents merging. Ships sink and they may cause eddies that look like whirlpools due to water displacement BUT they are not strong enough to do what you think of here especially since these boats SLOWLY filled up with water from the bottom up which means all the air was pushed out under normal pressures.
Kronos