Bang, Bang...
Michael --You don't say when you're hearing the banging, but from my limited experience (I owned a '78 C-25 for a year before moving to the West Coast and moving up to an '81 C-30) it's not too unusual and there's no real "fix."If you're hearing the banging when at your slip or at anchor -- are you leaving the keel down, or retracting it? You should retract it when not underway -- heavy as it is, it still could "work" (bounce up and down in the trunk) in a heavy swell if down and potentially damage the trunk and related gear to raise/lower it.If you're hearing it when underway -- I heard that from time to time, particularly when in chop (I sailed on the Potomac River at Washington, DC), again just from "working" up and down in the trunk. I think that's just a characteristic of swing keels, period -- and no harm done. BUT -- it's important to service the swing mechanism (the bolt mechanism at the forward end of the keel/truck that it pivots on) and the pennant (the cable and crank/winch used to raise/lower the keel) on occasion. The pivot point in particular tends to wear, particularly over long periods of time given the type of "working" I'm talking about. If it were to let go -- well, the keel would drop out. Extremely rare, so don't start worrying about i just because I mentioned it. But sufficient justification to check it from time to time and replace if needed. And if the pennant/winch assembly goes you're stuck either up or down, neither good. So the next time you haul her you might want to check both.Having owned both a C-25 and a C-30 I can tell you they're both wonderful boats. My C-25 was great for river sailing -- that swing keel can really come in handy -- and I had some great overnight experiences on the Potomac in autumn (and summer, too). I'd buy one again in a minute and it'll be my top choice if I ever go back to river sailing and gunkholing. And the C-30 is an incredible boat for the type of close coastal cruising we do here in Southern California -- a real "ocean sailor" in those type of conditions --and a virtual "condo on the water" when we take her to Catalina Island.Hope this helps or at least gives you some peace of mind.Oh, as to wind speed -- my theory is that any amount enough to sail in is enough! I'm usually worried about too much versus not enough. And when there's no wind -- that's why they invented shore power, microwaves and blenders...Mike TurnerS/Y AmityLong Beach, CA