Your Vagabond 17 sounds like a sweet boat.
Clearly you understand the first rule of a boat. Water must stay outside of the boat.
So many boats of this structure and age can develop cracks, holes, separation of joints, hardware bedding issues which allows water to violate rule number 1.
Tracking down such problems is a process of elimination. Slow and tedious.
You state that it happens “after a day on the water”. What were the conditions like?
- Calm and motoring
- Light breezes tacking back and forth small ripples
- Blowing sno, waves crashing over the bow. Exhilarating
Does it happen when you first put the boat in off the trailer or gradually over a long time period?
Are any stopper plug’s missing?
Does water splash up the centerboard?
Does it happen when you are sailing flat or heeling over 20 degrees?
I know this sounds like 20 questions. This is the nature of the beast.