Look in to the 500 or 600 size motors. The 12v version spins at slow RPM's and will use a larger prop. The hull might be a bit slower but will provide reliable power. Direct Drive is preferred.

The information found in this forum is for fast electric boats. You may be mislead if you read the information in this particular forum. If you go back to the main boating forum page and click on scale boats you could get a better answer from those guys as they run boats more similar to yours.

Ryan