I've done a search, but think my question is probably a little too specific, so I'll throw it open to anyone who is prepared to offer advice.

I have an upcoming trip with my father MEL-SIN RT on BA, and we're planning to add a SIN-HKG RT on CX. These would be two separate bookings, both in the Y cabin.

We're looking at connecting the HKG-SIN leg with SIN-MEL, and the flights that appeal have a 1hr 45min connection. The next best option is around 5hrs, which is less than desirable. I'm QF Gold (OW Sapphire), so we have lounge access to pass the time if need be.

I'm thinking 1hr 45min at SIN is a relatively safe connection, as both us and the bags will be checked through from HKG to MEL, but I'm just a little nervous that 1:45 is cutting it fine. At the end of a trip, the last thing I want is the stress of missing a flight. And should the CX flight be delayed and we miss our BA flight, are BA obliged to put us on the next flight?

Anyone care to offer their advice or suggest what they would do in this situation?

Cheers.

You should be absolutely fine. That's not cutting it fine at all - you almost have time for a sightseeing trip to the city!

Should be fine, barring anything unforeseen. Because Singapore doesn't have any domestic flights, the terminal is basically set up like a domestic terminal. You exit on to a common concourse and just walk to your next flight. Some of the walks can be lengthy, but (again assuming nothing unforeseen) 1h45 should be fine.

1:45 in SIN is plenty of time - you likely will have more than 1 hour to spend in the lounge.

If you are on seperate tickets and miss a connection it depends of the type of ticket. It is the same as if you are coming too late to the airport (traffic jam etc).
If the ticket is flexible you will be rebooked.
If not it depends. In my experience most non US airlines will put you on a later flight in this situation - even if the rules say that they don't need to. Maybee somebody has experience with this on BA.

1 hour 45 minutes is more than enough time for a connection at Changi, should be no problem at all.

Provided you can check in for the BA flight when you check in for your CX flight (which I think is possible on separate tickets, not sure - bags are no problem, but passengers?), you can cut it as close as 20 minutes between the flights. The OW gates at Changi are all pretty close to each other.

It would take something major to cause your flight to be almost 90 minutes late, so you should be good.

1:45 should be plenty of time in SIN. I'm doing MEL-SIN(QF) and SIN-LHR(BA) and I have only 1:10 for my connection. I'm sure everything will be fine but I have noticed that my QF flight has been getting into SIN late all week, so we shall see.

I regularly make a connection from QF51 to MH610 at SIN which requires a terminal change. The connection time is 1.5 hours and I always have time to have a snack and drink in the MH lounge before boadring.

These are normally on separate but linked tickets with the QF being e-ticket and MH being paper ticket.

I've had connections at SIN on *A airlines (different airline inbound and outbound) of an hour or less and made every one of them - although sweated a close call a couple of times.

The only problem will be if inbound is significantly delayed (more than an hour). As its separate tickets the airlines have no obligation to protect your continuing flight. What happens will depend on fare rules of the second ticket, your status with them, also how much of a delay and how many passengers affected (eg if you're the only ones and first flight is 2 hours late they probably wont hold the second flight, but if there are lots of connecting passengers on those flights and first flight is 80 minutes late they may well hold the second).

In situations like this I try to make the second ticket flexible enough to cope with missing the booked flight, and also a backup plan for what I'll do if miss it.

DO you have connecting luggage?

BA has lately been pulling excuses as "IATA EU rules state that...." when presenting 2 seperate tickets at the BA check-in counter in Europe that BA cannot check through luggage to final destination. I don't know if they will pull that excuse over in Australia.

But a 60 minute connection within T1 in SIN is more than possible.