We are going to install a bow-thruster and are wondering how best to wire it.

The motor will draw 500 amps, but of course only for a very short time

We will install a good sized starting battery beside the thruster.

One problem is that the alternator is only a 70 Amp Volvo unit. It has been OK for years, but all it does is charge a small starting battery. (House system is separate, with its own alternator. For a number of reasons we do not want to use it to feed the thruster)

Questions are
1) Will the heavy load on the battery running the thruster burn out the alternator?
2) If we install a 70 amp breaker to avoid overload on the alternator, will this cause diode problems if it pops?
3) Any ideas on how to protect the alternator and diodes .
4) Does the alternator even need protection, given that the high load would be for under a minute?

Thanks