Hi Mr Norway. Boom to boom is more difficult particularly if you run a high boom. Easiest way to get Vulcans consistent is to grab the mast. This lowers your centre of gravity and you can tuck up into a compact ball . So try this method... front hand as far forward as possible ,nice and early then go looking for a nice steep bit of chop upwind. When you have spotted your steep ,upwind chop ,pull the rig slightly back and head upwind to meet the ramp. Going upwind kills some speed and the steep chop launches you upward.try to do a slower more vertical jump so you don't end up sliding backwards at full speed this makes the odd of staying in control and completing the move greater.The grabbing the mast method will also force you to change. Change is good .
Grab the mast with your back hand as early as possible, while your going up the chop ,before your board has even gotten air.Then let go of the front hand as soon as you have grabbed the mast. Once in the air REEF the hand holding the mast back to the direction you came from, your head should also now be looking at the horizon where you came from with arm that's holding the mast straight and pointing back in the direction you came from.
No rush to grab the boom with your back hand, you can slide backwards and balance just holding on to the mast with 1 hand. When you do place the new backhand on the boom, don't sheet in aggressively as your rig will be leaning forward because you have the arm holding the mast straight and you will just catapult.
PIC1-Your back hand should already be holding the mast and have let go of the front hand. You should already be REEFING the mast back to the direction you came from.
PIC2_Your hands are actually both in the right place BUT the left hand should be holding the mast and your right hand should be free

So your rig is leaning the opposite way than it should be.
PIC3-Your looking downs that's where you will end up

You should be looking at the horizon at the end of your wake/trail ,just downwind of the fuzzy/droplet on the photo. In preparation for the move (moving front hand forward.....then looking for ramp) look for a tree/pole/ house /car ect on the horizon where you came from. You should be focussing on that spot (not at your wake/board or boom)in both PIC2 and PIC3 and REEFING your hand holding the mast towards that point
They say that the carve gybe is technically the hardest move in windsurfing. Well the Vulcan is the gybe but it is completed from the time you take off till the time you land. They are hard to master and take a while.Once you have the Vulcan it doesn't take that long to crack the Spock/spock540 or most other moves.