Cutting straight with a band saw

[sheryo]

Hi all,

I have a sawing question:

I have a piece a material: half cylinder 10" radius
30" long of hard composite foam.
I need to cut that in 3 pieces: 3 half cylinders 10" radius
10 " long.

I am not experienced with a vertical band saw.
Can someone explain me how to do a nice straight cut with a band saw. Should I use a guide? How do I account for
blade lead?

Any help or ideas would be very appreciated.

Thanks