Physics Project: The Famous Foil Boat

[Yoomin]

Homework Statement

I know that (for a given mass) the volume of an object affects its density. The greater the volume, the lower the density; the lesser the volume, the higher the density. Thus, the lower the density, the more pennies the boat can hold before sinking.
My question is, how can I increase my boat's volume?

Homework Equations

The Attempt at a Solution

As a geometry and human anatomy & physiology student, I had to research all the basics of buoyancy on my own.
I've asked my math teacher how, but she doesn't know how, as she's my geometry teacher. Prior to asking, I've typed many variations of "how to increase volume" in search engines, only to find "how to increase semen volume!" and the such. :(
Thank you in advance.

 

[Sethric]

Are you there rules for the amount of foil used?

Since it's all about volume displaced, you can make the hull deeper; you can also scale the boat up, since volume goes as $$r^3$$ and surface area(weight in this case) goes as $$r^2$$.

 

[Yoomin]

There are no rules for amount of foil used.
I'm sorry, what does r stand for?

 

[Sethric]

Just radius in general. You know how people make jokes about physicists approximating things with spheres? That's what I was doing. But it remains true. As something "gets bigger" volume grows quicker than surface area. So a larger boat will displace more volume of water per amount of foil. The limiting factor is structural integrity of the foil, I guess.