Why did my 12 volt dc blower motor quit?

I actually asked a question about DC motors earlier tonight. Let me explain in greater detail. I am building a very small pontoon boat for an engineering class and I set up a 12V DC blower motor with paddle wheels to propel the boat. I ran the motor 3 times and suddenly quit with no warning of malfunctions. I hooked a 7.2V battery to it and it quit. Then hooked the 12V source back to it and nothing. It quit with the 7.2V source. Also, no time for rust to set up. Ran the trials in 45 minutes. No, it was not sealed. Any explanation or was it just the water? The motor was sumerged. Was told by older fellow that the made trolling motors out of the same blower motors and it would last 3 fishing trips.