Hi gillespm,
Theoretically there is only one bilge, that's the area under the sole - maybe you're asking how many bilge pumps?
Bilge pumps:
My 170 has 0 bilge pumps since there is no way for water to get in there - the sole is complete and watertight. I have been thinking I should cut an access in the rear deck and put one in the bilge in case I hit something and puncture the hull. My 230 has 2 bilge pumps, one about midship and one in the aft.
Drain plugs:
My 170 has 3 drain plugs - 1 for the "bilge" and 2 for the deck area (above the sole). My 230 has 4 drains although there is only a drain plug in the single bilge drain. all are the size of a typical drain plug and can be plugged.