Remember (these in my words):
One short blast means “I am altering my course to starboard”
Two short blasts means “I am altering my course to port”
Three short blasts means “I am operating astern propulsion” AKA going in reverse
Four short blasts mean “I am turning around in the fairway” one more short blast “to starboard” or two more short blasts “to port”
Five short blasts means “I am about to crash into you if you don’t do something” – generally move out of the way of the big boat NOW
One long blast means “I am coming around a corner or blind spot. Beware I am here.”
I hope this helps. The Rowing Code gives you the full details.