Type of wood used for spine?

[spareparts]

based on what I've seen with general boat construction, including my own V20, teh wood is merely there for teh glass to fit over, creating a box type structure. There's no structural value for the wood itself, more so the glass covering it. Ive seen several boat manufactures using 1/3 cut pvc tubing in the bilge and covering it in glass, the glass itself creates a rigid chamber, the pvc just gives it shape. It allows water to drain thru that channel, even more so if you put limber holes in it for each bulkhead area.