I should have added - in my case, I found three things to fix, and two to live with
1) at speed, water was pressing up through the rudder gland. Filling the relevant area of the rudder tube with grease periodically, mitigates that
2) at speed, water was pressing up through the near-the-waterline bilge-pump outlet, past the anti-siphon loop and into the bilge. New anti-siphon loop and some hose re-routing fixed that. Note that centrifugal pumps do not act as check-valves in the way that diaphragm pumps do, so if there's water in the hose, it will come right through the pump and into the bilge (unless you install a check-valve, but anecdotally that hamstrings the effectiveness of the pump, and doesn't really solve the problem - it simply makes it so you have a hose full of water instead of water in the bilge.)
3) it appears (?) that some small quantity of rainwater comes into my boat through the cockpit scuppers. I suspected that the scupper fitting was no longer properly bedded but I addressed that and still see some signs. My guess is there's a crack in a scupper hose. It's "on the list" to fix, but as it is sporadic, not harmful, not a safety issue (the hose is above the waterline from end to end), merely annoying.... it's not currently at the top of the list. I also suspect that one of my cockpit hatch lids allows some rainwater in. Same story. On the list to fix
the two I have resolved to live with are
1) rainwater. Comes down through the mast and into the bilge in surprising quantity. No real way to prevent it.
2) whatever water you "think" you've emptied out of the bilge, there's more lurking in hidden resources under the structural grid, and it will come out into the main bilge when the boat next heels. No real way to get rid of it. Best I've found is to dump some bilge cleaner into the bilge a couple of times a year and slosh it around during a sporty sail so that, at the very least, when that mystery water shows up later it won't be so stinky.
