Chuck, Does your boat have a battery already?
If so and if it is a deep cycle marine then an electric might be the best bet.Before buying a electric motor I would check with the engine manufacturer about the size motor required to push a boat with the weight of a 170 and for the amount of time required to return from the longest distance you might be sailing if the wind dies, which it will do. It could be that the battery demand is so great that it is not practical. Small gas motors sometimes have the fuel tank mounted on the motor, thus being 1 unit. Remote tanks do have a longer range which might be required. The weight factor of a gas motor might be less than that of 1 or more batteries. I have a Honda 9.9 four stroke on my 95 H26 and can go a full summer on one 6 gallon tank of gas. That much fuel returns greater that 12 hours of run time.RayS/V Speedy