After you set it, you usually have to apply it if it hasn't been done prior. Perhaps after the filter setting line:
Code:
Forms!F_OwnsBoatNewEntry!F_Cust_Sub.Form.FilterOn = true
I recall reading issues about altering form filter more than once but can't recall what the details were. Something about the first filter being re-applied if it wasn't removed first?
EDIT - don't think you should have the trailing double double quotes though
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.