pigboat's quote is spot on. I was awaiting return to my library to dig out the same information.
Operating out of FAJS (hot and high) in both the HS 748 and the F27, we often used WM for take off and always had it turned on during final approach in case of a go around.
We also used to execute a 'reduced power take off', brainchild of the then Chief Pilot.
Advance power levers to about 14,200 RPM, nip down the runway and if it looked as though you weren't going to rotate by a chosen point, advance the levers to enage WM. A lot of us thought that this was slightly dumb?
One important lesson was never to arbitrarily switch on WM during a dry take off with power levers at maximum. That would lead to expensive noises as little bits of engine tinkled out the back.
On the F 27 in England, flying for a major operator, we were forbidden to use water methanol at all, even on the hotest days. That company also had a peculiar operating policy for the fuel trimmers which ran quite contrary to Fokker and Rolls Royce's own operating manuals.
I seem to remember that both aircraft carried thirty gallons WM (US) a side. It was possible to run out of WM halfway through a take off or go around. Three wet take offs for a full tank each side was a rule of thumb. Thus, if you had five gallons a side and needed wet power for take off, it was time to top up the tanks before departure.
