I have a Carvin fretless, with ebony fretboard. I have played with Thomastik jazz flatwound strings for several years. I started with flatwounds because I reckoned that the roundwounds were doing too much damage, but I think these flat wounds are are doing more. The edges of the tape seem to cut in to the ebony. Does anybody else have this experience??
It sounds like you might need to work on technique and don't "fret" quite so hard. As well, TIs are very flexible, so you'll probably want to work on a lighter touch. I have not experienced this problem with any strings on my fretless basses.
+1. Sounds like you're digging in pretty hard. If you don't already, keep your vibrato running parallel to the string and avoid 'guitar' vibrato that bends the string across the neck.
Sounds like an aberration to me. I've been using TI flats on my fretless electric basses for more than a decade (and TI Spirocores [flats] on DB since the late sixties) and have never experienced a problem like yours on rosewood or ebony fingerboards. Can you post photos that show the damage?
Just because a string is flat or round does not mean it will do more or less damage. T-I's have spaces between the windings which makes them that much more flexible, but that can also create grooves in the board. I see these grooves nearly immediately on my fretless w/ ebony board... I will take similar photos when I get back from jury duty today... Flat or Round you are to expect some kind of markings... Afterall there is something of a harder material vibrating against a wearable surface. Your fingers alone will wear the wooden fingerboard without any strings in place if you rub your hands across it enough...
Ebony is pretty tough stuff. Even if you are showing some surface wear, that fingerboard will last for a long, long time. When it gets too worn, you have planed and resurfaced... many times in fact. Use the string that gives you the sound and expression you want. The fingerboard is a wear and tear item and may have to be replaced some day.... oh well. Same thing with the brakes on your car, doen't mean we don't drive. I play double bass as well, same thing. In 50 years, my bass will need to have the ebony board stripped off and replaced. I do not spend one second thinking about that. Every brand of string will eat your frets or fingerboard. Thomastik is no better or worse than most.