Hi.
I owned a 1972 C&C 27 mk2, a 1982 C&C 27 mk4 and a 1974 C&C25mk1. I've also inspected and sailed the C&C29 mk1 and C&C 30 mk1. I consider myself an expert on these great old boats.
Lets talk about your issues.
Spider cracks...they all have them, nothing to worry about. Check for softness. If there is a nice "ping" when you tap, its good.
Keel bolts. No way to check without cutting open the
keel. The pictures look good. I've seen much worse. In all likelihood they are good. I haven't heard of any failures yet.
Creeks and moans when walking about the deck above and below...get used to it. They boat is going on 40 years old. Wait till you go sailing in a big
wind, the boat will pretty much sing as it grunts and groans. I thought the bulkhead tabs were pulling out of the
hull once, but it was fine.
You found with with a
yanmar once cylinder engine. These are rare on the older models...and an excellent find. A great engine that will last forever when maintained. It may vibrate the hell out of the boat, and drive you crazy, but it won't let you down. Best to have a sea trial and take the
rpm up to speed. Watch for the engine "dancing" at resonant rpms and at idle. Also, be sure the controls are good...be sure you can idle, and shift easily into and out of forward and reverse.
Check the prop shaft for drips at the stuffing box.
Here's a BIG one...make sure all the original GATE valves have been replaced with BALL valves...very important...you may not be able to
purchase insurance without this. And while down there, check the
cockpit drain hoses for cracks and all through hulls for double hose clamps.
Most of these boats that have been maintained are in really decent shape for older boats. They were constructed with a high build quality and that is really shining through now that they are getting old.
If possible, check the prop shaft strut (holding the shaft near the prop). If the boat is in the water, you may need to go for a swim....if it wiggles...big trouble, should be solid. And the shaft should be solid in the cutlass bearing. Replacing the cutlass bearing is a little part, but a big job requiring pulling the prop shaft.
If the boat is
on the hard, check the
rudder for water. Once water gets in, thats it...new
rudder needed eventually, or after one
winter here.
The pictures you show all look good. I don't see anything that would stop me from moving forward. However....around here these boats are really common and inexpensive. $7500 is at the high end of the market, and should be justified by that diesel. You are
buying a great diesel engine, wrapped in a sailboat...LOL.
And finally, the original SS
rigging is well past its best before date. If the standing rigging has not already been replaced, plan on replacing it all. This isn't actually that expensive, just a bother.
Please let us know what happens, and if you have any more questions, I'm happy to help. If you aren't too far from Kingston
Ontario, I'd even go have a look for you. Thanks for asking about these great old boats...you made my day.