my book is sayin 20 deg +/- 1, it's not the best idea, but , i have done it with a prop. run two ropes from the back of the trailer to the bow eye, strap the transom down, cranked right up to the post. back in till the cave plate is in,
still all strapped down , fire it up, trim up a bit so she's throughin a tail,make a pull, ckeck it at 5000rpms, i'd hit at 21, thinkin your rev limited. be careful, ya don't want it in your tow rig
watch your water pee toob .
or have a friend drive, on a flat day.