|I can't claim any experience-based expertise on the matter of transocean sailing, but I can tell you where you will find a lot of knowledge, in the offshore racing guides to preparation and their attendant mandated equipment lists. The following are based on discussions with sailors who have sailed across oceans, a lot of reading and a lot of racing around the lakes.
Almost certainly, you're going to want:
- real seacocks to replace the throughhull/gate-valve combination that C&C used up to the last 27's, along with softwood plugs and a mallet;
- a vented loop in the exhaust line to prevent large waves against the stern from creating a siphon back through the exhaust system that destroys the engine;
- a vented loop in the head inlet line;
- stronger lifelines and jacklines, with reinforcing plates under the lifeline, pushpit and pulpit bases;
- positive locks to prevent the companion board from sliding out if you are knocked down, with a similar lock on the companion slide;
- seriously beefed-up battery hold-downs to keep them in place in case of a knockdown;
- LED nav and interior lights to minimize electrical demand;
- ridiculous numbers of powerful waterproof flashlights with lots of spare batteries, all located where you can find them easily while blindfolded (blundering around in the dark and not accomplishing anything seems to figure largely in many yachting disasters).
I'd also have the rigging replaced, or at least inspected.
This is really the beginning of a list -- I know a fellow who sailed the Newport-Bermuda Race and he had a mandated checklist and set of standards that filled three large binders. It's only a start but I hope this is useful.
C&C 27 Mk IV
PS I've heard that someone sailed from the southern US to the Mediterranean, but no details. The Ireland adventure was from Dublin to Norway and back, a trip made incomparably more difficult by the tidal currents around the north of Scotland.