Wet wood inside fiberglass. I spent 4 years in the USCG and saw so many issues from that. Especially in the bilge where inboard motors attach. Who would think that if you drill a hole in fiberglass the core would get wet.
On a driftboat the ob is mounted a long ways from the bottom and gets plenty of flow. But, no matter what, you need enough shaft to get the prop into the water.