Buoyancy is the force that keeps objects on a liquid from sinking. It is equal to the weight of the water displaced by the object. My boat is a stretched cylinder that his hollow but it is open from the top to lessen the weight and increase the chances of floating, this is because the boat will hopefully be lighter than the water displaced. The cylinder is connected to four hollow spheres which will make the boat impossible to capsize and since the are hollow, they will not take up much weight so it will still float.
The maximum amount my coins my boat could float with was 2. My boat didn't do well compared to others because my boat was fragile and unstable and when added weight the boat capsized. Other people had a more solid base than me and the pontoons were directly touching the foundation when mine were connected with a thin rod.
Instead of having four hollow balls connected by thin rods I would have hollow cylinders that would be under the boat and wider than the boat so it doesn't tip over. I would also make sure that the hollow cylinders would have adequately thick skin so there come no holes but still thin to make my boat light.