You can "experiment" with your NTrance quite easily to see how getting upwind
without the centerboard (CB) works.
If you were to get a new board (without a center board), at your weight I'd suggest a
slightly wider and more lightweight board than the GO 155.
Here's the technique:
Instead of keeping your board as "flat" rail to rail as possible (gets you planing the earliest) try stepping off center toward the windward rail slightly.
The idea is to tip or "cant" your board so the rocker in the bottom will take you upwind
due to it's shape.
You don't really need to "rail" your board all that much to get the water flowing under the "canted" bottom shape to steer your board upwind.
The largest difference is going to be rig positioning (steering).
Currently, to go upwind with the CB fully depoyed you rake the rig back (clew end of the boom down slightly) and your board steers upwind because you've moved the Center of Effort (CE) in your sail back toward the fin (relative to the Center of Lateral Resistance (CLR) created by the fully depolyed centerboard.
(I hope you either have it all the way up or all the way down (deployed) as partial deployment (say 45 deg.) really doesn't work and makes your board very hard to steer as the lift from the CB is not positioned correctly relative to the rig and the foil is very inefficient went set at 45 deg.)
So, if you raise your CB you lose the CLR of the CB. Now you only have the fin as your lateral resistance, and in sub planing (slog) mode the fin does not have enough water flowing by it to give you any real lateral resistance.
You need to "create" lateral resistance further forward under your board.
You do this by tipping the upwind rail down a bit so the board wants to "follow" the curvature of the rockerline and your course will be more upwind.
BUT, if you tip the rig back, at the same time you tip the board upwind rail down (to create that forward lateral resistance) the board will very quickly "round up".
It's doing exactly what the forces acting on it are telling it to do.
So, here's the "big trick".
You tip the upwind rail down to create the necessary "upwind surfaces", but you tip the rig forward slightly to "steer" the board.
If you want to go more upwind, tip the rig more nearly vertical (i.e. tip it back slightly).
If you want to steer the board off the wind slightly, tip the rig forward a little to overcome some of the board's tendancy to "follow the rockerline".
You can do this on your NTrance (or any other board).
Will you "have trouble" slogging upwind without the CB?......... right at first, yes, it will seem difficult..... but soon you will learn how to balance/steer with your rig and the board tipped upwind rail down and it won't be difficult at all.
Want to go higher..... tip the board a little more.
It's better to keep the rig pretty much upright (or somewhat forward of upright) and sheeted in only enough to give you the best forward drive.
If you sheet in too much, the rig will stall and the board will go pretty much sideways.
Give it a try on your NTrance and let us know how you get on.
Perhaps something like one of the larger Futuras will be in your future.
You need a board that's a minimum of 85 cm wide to get the best early planing.
Wider gives better early planing, it's that simple.
Hope this helps,