Strange Leak

[Harvey]

I have a 1981 Potter designed Seacraft SC 23 and I have a strange problem. when boat is at mooring all is dry. If I power along in calm water at about 28mph
water enters bilge. If I turn on pump every 10 minutes while underway it will pump salt water out for 10 to 15 seconds. This continues till boat is at rest or at mooring. I am told it might be a scupper problem which I am unable to find. I have sprayed water from garden hose at and in scupper while boat on trailer but nothing definitive. Is scupper inside a fiberglass shell or is fiberglass the scupper.
Appreciate any input and thanks
Harvey/Marion, MA