There seems to be an opinion that SIDS are based on a specific number of engines. I would suggest that they aren’t! They are based on TERPS / ICAO ANNEX 16 (I believe) and involve a specific gradient.
This gradient is designed to get the aircraft clear of obstacles, noise, ATC crossing gradients etc etc. The reasons behind the specific gradient isn’t available to you as a crewmember, all that you know if your aircrafts climbing ability with all engines and one engine out.
Therefore your only safety is your knowledge of your aircrafts abilities!
Now for a couple of questions:
As for the idea of flying straight ahead, just how far are you planning to go?
With FMC equipped aircraft, would it not be easier to fly a programmed SID rather than flying straight ahead?
Thanks.
Mutt.