thru-hull

I have an Irwin 41 that I'm gradually figuring out, but my most recent finding is that the plumbing from my center cockpit drain goes down into a seacock/thru-hull fitting uneder the waterline at the bottom of my boat. I don't quite understand this configuration. The cockpit sits high out of...

I need to replace my depth and speed instruments (original from 1979). What is the performance difference between a thru-hull and in-hull depth transducer? Is my 1970's fiberglass too thick to use an in-hull?