# Displacement of water for a boat and raft

## Main Question or Discussion Point

If you have a perfectly flat, rectangular raft and a perfectly flat, rectangular boat, which will displace more water? Or will the water displacement be the same.

I remember that the water displacement is dependent on the shape of the floating object and the weight, but I can't remember exactly how to calculate the water displaced.

This is for a cardboard boat design in a pretty shallow creek, so vertical displacement is the most important factor. Thanks!

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DaveC426913
Gold Member
First thing we need to understand is the functional difference is between a raft and a boat in your world.

I am going to guess that the functional difference between the two is that a boat is a hollow rectangle, whereas a raft is a solid rectangle. Would this be correct?

russ_watters
Mentor
...assuming that's the case and assuming the mass is the same, displacement, as Archimedes figured out, is equal to the weight of the boat/raft, so....

DaveC426913
Gold Member
... assuming the mass is the same...
That was going to be my next question. The OP has not provided enough detail and I wasn't prepared to take it for granted (If you assume the mass is the same then there is no functional difference at all between a raft and a boat). I figured I'd tease it out of him while he worked it through.