Dear All,
First I will introduce myself I am a computer programmer and a electronics hobbyist , we own some fish ponds , fish die during overstocking I decided to build an Unmanned Surface Vehicle, I have already programmed the computers and worked over everything The only think I am really struggling with is the design of boat , i tried creating a square box with a plastic fan and brushless motor of a quadcopter but the issue is my boat doesnt do straight it just start going towards the bank of the pond. I have zero idea about the rudder control (i know i can control it with a servo motor) , secondly my boat is small not larger than 4 feet * 2 feet. My boat has an oxygen sensor which will keep on sending me data for the oxygen currently in water.
I am writting this post for helping with the
1. which motor and propeller would be better for such a small boat? it is not a racing boat it needs to go slowly and only run when it is needed.
2. any other design options which can help me in creating such boat?

Something like this.

Autonomous R/C Boat 13km Waypoint Mission (19 min 19 sec)