Designed using parametric equations and Calculus! 
(And kids still say, “when am I ever gonna use this?” … for shame!)

Three polynomials (one for each axis) describe a beautiful curve in 3-space for half of one side tube. Then cap it off with some slightly diminishing cylinders (using Calculus to get the angle to match the end of the aforementioned curve). Reflect twice to get the full outer tubes.

The floor is a squashed, elongated sphere that's been curved up on both ends to match the rocker of the side tubes – circles made with 16 segments to see the ridges on the floor (to mimic an I-beam style floor). 

The holes between the floor and tubes allow water to flow OUT of the boat (when you hit big waves!), called “self-bailing” – since the floor and tubes are all full of air, they float even if the floor-to-tube connection is not watertight. Print one and try it yourself in the sink or tub!