I'm not sure what you mean by "rational", but certainly there are consistent, "systematic" ethical theories that one could arrive at from first-principles. Think Kantianism, Utilitarianism, Egoism, etc. If you were to ask philosophers whether their pet theory of ethics was rational, I suspect many would answer yes. Any theory of ethics that subscribes to ethical naturalism would answer that with a definite yes.

If you are going to have a contractarian position on morality and you don't want to end up thinking that morality is nothing but Machiavellianism, I suggest you read some Rousseau or Rawls (basically anyone who isn't Hobbes).