This is a complicated situation. Do you have duro torque or leaf spring suspension on the trailer. What type tyres and are they at the correct pressure. Has the toe and camber attitude of the tyres been set up correctly when the trailer was made. All these have an affect on the tracking stability.
For a general weight distribution, you divide the entire trailer/load balance into a 60/40 ratio. Yeah I know, how do you do that?
But anyway, 60% of the overall weight should be forward of the trailer axial.
Here are some effective and possible remedies. Depending on the exact problem, each may or may not have an affect. Depending on tire type, try changing the inflation pressure. Try a much harder inflation and then try a very soft inflation and see which has the better effect. Try taking the weight in the boat further forward. A very effective mod you can do, is to fit shock absorbers to the trailer axial. That makes such a difference to how any trailer sits behind a vehicle. Ensure Springs, if fitted, have no shackle slop and the springs themselves are not too extreme in their curve.
Hope this helps.