Prop shaft seal questions

I am pondering building a pedal boat, and using props run out the side of the hull. Since the shaft and prop will be below the waterline, the shaft needs a seal. The boat will be fresh-water only, and since this is a "car-topper" size, the boat won't be stored on the water.

I don't know a thing about these types of shaft seals, other than McMaster-Carr sells a bunch in a variety of sizes. The buna-s ones say they are for water pumps; I'd guess that is what I'd need.

http://www.mcmaster.com/#shaft-seals/=89tyxw

Are these basically the same thing that boats use?
Do boats use more than one in-line?
Does the seal need to be backed up with oil?
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Seals for water pumps will work fine.