One problem I had with the Paula was that it had a relatively short run time per battery charge, especially considering it was using a 5 amp/hour battery.  To address this, I change the motor that came with the kit to one that would draw less current.

Phil over at Vac-U-Boat gave me a motor to try.   It is a 12 volt Mabuchi Heavy duty RS540.  Even though it is rated for 12 volts, I ran it off 6 volts.

The original motor is on the left, the new one is on the right.  You can see the it is a bit shorter then the original.  The shaft size is the same as are the mounting holes so it was a simple swap.

The new motor was a lot slower then the original while running off of 6 volts.  In fact, it may be too slow for some but the run time is impressive.  I ran the boat for around an hour and a half and only used up 1 amp/hour of power.  The actual speed is probably pretty close to scale (which is slow) but there is not a lot of reserve power for towing things if that is what you do with your Paula. 

Better results may be possible with a 7.2 volt NiCd pack, I'll test that next.  For now, I will live with the slow speed and enjoy the much extended run time.