3.5 hp is 41 pounds. the 4hp is 57 pounds. (per defender Website) That's pretty heavy to be muscling around. I don't even like the 41 lbs of the 3.5 but that's me. you need to pick the outboard based on how you plan to use it. For instance, I have a Honda 2hp at 27 pounds. I keep the motor on the dingy as it hangs from my davits. I use it primarily for just trips between shore and the boat and it meets those needs. So weight is an important factor for me where as if I was to use the dink for long trips, Horsepower would be more important.
2007 Hunter 49