Mark,
That's a pretty large crack. Does the armature look like it is intact? If the armature is good, from what I have learned on my boat, I would clean out the crack, coat it with epoxy and when it gets tacky, fill it with a mixture of epoxy and portland, about as thick as you can mix it. It bonds well and seem to hold up, although mine hasn't stood "the test of time." You can also add a small amount of fine sand if you wish. If the armature is damaged, you have a structure problem and a completely different issue.
A good bonding agent if you choose to go cement, is acrylic that is sold at home building supplies. You can coat with it first and then mix the agent with the portland instead of water. (Acrylibond)
With that large a crack you should be able to go in and expose the wire and then force the filler in and around it.
Colin Brooks at ferroboats.com is the authority and he responds very quickly to e-mails. His book available from the site and is an excellent guide.
Sam Cowles at
ramprasaduk@yahoo.co.uk is also very helpful. He is usually cruising but returns e-mails. He has made many transatlantic crossings in the boat that he rebuilt. It's an interesting read on his web site.
Good luck, Ellis