Re: Is the C&C 30 MK1 a capible offshore boat?
You are probably fine for what you are wanting to do. C&C's are generally well built, well designed boats capable of pretty much anything you will experience coastally (just don't go out in hurricanes or tropical storms). I go out into the "ocean" with my old hunter 25 regularly, so you should be fine on that boat, again provided you keep an eye on the weather. Just make sure you have at least two reef points on the main, and ideally a %50 jib or some other type of "storm" foresail. If you have no "storm" jib, practice unfurling your genny 25%, and make sure you can make progress upwind with it. Don't rely on the motor for when the wind comes up. Also practice heaving to, and doing sail changes and reefs while actually under sail. (Reef the main by either going upwind and keeping the jib sheet tight while blowing the mainsheet but maintaining your course, or by heaving-to and reefing the main. Change the jib by either "peeling" the new jib onto the second headfoil slot, then tacking and dropping the original jib, or else by running downwind and covering the jib with the main to allow you to get it down onto the deck and put up the new one.)
If you are talking about doing a trip to Bermuda, that's a different story. The boat can probably make it, but will have to be modified to ensure ISAF compliance. You can find the ISAF offshore rules online, they are extremely helpful in identifying the seaworthy and the not so seaworthy features of your boat.
My father has an '82 C&C 32, and it is a very high quality boat with wonderful sailing qualities. The hull thickness is more than adequate, only the lexan ports were original and held on with glue. They were coming off so we re-glued and through-bolted them. The hatches are original and leak when waves wash over the deck, getting the v-birth wet, so will eventually be replaced though it is rare to get water over the deck generally so we are gonna leave them for a few more years.