Hole using Boolean

 From:  turnrock
6303.1 
Hi everyone,
I have a model i made and i want to blow it up then cut it in 3 pieces so i can print each one filling up most of my printable space and in the end i will glue them together for a very large print.
The problem im having is when i try to Boolean it im left with a hole.Im still pretty newb so im not sure why this happens sometimes and other times it works how i want.
Anyone have an idea of what i can do to cut this up and keep it watertight?
Thanks in advance
Aaron

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