Hmm, is there not another way this can be adjusted?
I was wrong, they have counter rotating in 4-stroke.
Than i would guess that the engines are to high, my old boat had 2 X 300HPDI and only 8,2m long boat and my wobbeling came around 59-60 knots.
I lowered the engine and it disapered but than i got the galopping effect instead.
But the boat was a little over powered, with 2 X 250 i would never have the problem.