I know what you mean about the weight. My parents used to have a little 1 1/2 hp that weighed less than an electric motor. I, personally, would not trust my getting back home on solely an electric motor when dealing with tides or rivers. The other thing is be sure to rinse that motor really well after using in the salt and be careful about wind blowing salt water up into the head. I have had at least one go belly up because of corrosion.
If you need foam, let me know. I know where a fridge sized piece is washed up above the high tide line.