sorry George, with respect, I don't agree with you
If the bow of the boat is higher than level (has nothing to do with the trailer frame) and you drive with the window down at 60 mph you will hear a loud clunk as the semi passes you, that is the hitch coming up on the ball lifting all the tongue weight up, most trailers will give a little sway at this point. Lowering the bow down below horizontal and the effect disappears without changing anything else.
You will not get this effect if you have a weight distributing hitch. If you have a sway problem try to lower the bow of the boat before spending money on a weight distributing hitch, it is a lot cheaper solution. I did not dream this up, this effect is well known to many experienced trailer sailors and easy to test for yourself.
I just towed our H260 4000 miles, much of it through the mountains in the winter with just the regular trailer hitch that GM supplied with our Chevy 1500 pickup truck with the trailer towing package, never once did we experience any sway under any conditions, the bow is adjusted to be down just slightly.
If you have ever tried to carry a sheet of plywood on a windy day you know the effect of just changing the angle a little.
If the bow is down too much you can have problems with premature brake wear and reduced gas mileage

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