"6E9 indicates it's 40 hor
"6E9 indicates it's 40 horse Mariner built by Yamaha for Mercury. Most likely a "C" model produced some time in the 1980's.
That's not alot of horses for an 18 foot "glass" boat that has a dry weight of 1300 pounds or so. Add a couple hundred pounds of motor, a passenger or two, a battery, gas, gear etc and that 40 is going to working awfully hard to even move you away from the dock.
A boat that length/weight would normally be fitted with a 90 to 125 horse power option if you were looking for it to perform as designed.
Personally, I would consider a 75 horse to be the absolute minimum horsepower you would want to go with on that particular rig."