Maybe it's my eyes or the picture resolution, but the holes in the arm on the water rudder look pretty large - this may be a silly question but is are they a tight fit to the clevis pin? If so, I'd say one source of centering problems/slop may be the fact that you have several linkages in series - rudder servo to nose wheel (2 linkages) then nose wheel to water rudder (another two linkages), with ganging clearances. That coupled with the short moment arm looks like you have on the water rudder arm may be casuing some uncertainty about center. Slop is fixed, for a given hole diameter and clevis pin diameter. If you moved the clevis on the nose wheel arm to one of the outer holes and used a longer arm on the water rudder you might tighten things up a bit by reducing the amount of rudder movement due to any slop that may exist in the linkages. But as others have said, it will be under load in the water and may be less of a problem than you think it might. MJD