In the morning I'll be attempting a foil behing a cat style day boat with 65hp.
My wanted help is the starting ie getting up on the foil board.
I can to a very beginner level foil in light wind with kite.
Whats the easiest start technique please??

Starting is the same as wakeboarding behind a boat. Have feet already in straps facing the back of the boat at this stage board is vertical. (perpendicular to water surface). Get driver to drive forward, eliminating any slack in the rope. Then driver go full throttle until you're up. Driver then can slow down a little bit until you're comfortable with the speed.

Once up on the board, try leaning more on your back foot which will cause the board to rise on the foil. (Much like kiting)
You will find that the foil is more smooth and predictable away from the bubbles and wash caused by the boat's propeller.

I'd recommend wearing a helmet first few goes. I've had a lot of near misses almost falling head first into the foil. (usually when it stalls when going too slow)

Thx
Your advice will be applied.
Stay tuned.

Based on advice I did it behind a boat.
But much better fun with a kite.

Nar sorry loftsofwind, no need to floor it on the boat, this is just gona make the foil leap out of the water straight into a nose dive for a newbie. Slow on the throttle is best I found, about 40% of what's needed for a wakeboard. This gives the rider time to twist the board forward and apply front foot pressure as the foil rises.
It just makes sense, why would you want a huge burst of power the first time you get up on a foil? At first you're not even trying to fly so as slow as possible is best, that's the whole point of using a boat~

Boat power to get up depends on the boat and it's available power.
Now I am an expert, ie tried behind a 5 hp tinny and larger day boat with 65 hp four stroke, tinny with older 5hp full power was not enough however 65hp 4 stroke at about 1/3 power to get up was easy.
So both guys above are correct

Start with your back foot out in front of the strap so the board stays flat . On the start immediately cut out on your forehand side before the wake develops and straighten up , this puts you in clean water and you won't have to cross the wake. Keep the board flat then slowly creep your foot back. It helps heaps if the boat has a wakeboard tower or ski pole , it doesn't pull you down. Don't cut away from the boat when trying to foil if you fall the foil flips up towards your head.