Most people using and even building trailers are not engineers and the "rule
of thumb" is usually good enough for them. I've built 100s of trailers and
never needed to resort to a finite stress analysis or calculation of polar
moments to design a good trailer. However, knowledge of how these affect
the performance of the trailer is important.
BTW, I've seen trailers with very small tongue weight that tow just fine and
others with the "recommended" tongue weight but and unbalanced load (i.e.,
high polar moment) that sway all over the road.
The suggestion to: "Get the boat where you want it. Then make the tongue
the length you want
it. Finally move the axle to get 10% of the weight on the tongue.", is a
pretty good one... but 10% may be too little or too much depending on the
design and towing vehicle.
I've also build trailers with movable axle/spring frames to allow the
trailer to be blanced to carry different boats.


"Floyd in Tampa" wrote in message
om...
Now I wonder how we ever made it to the moon, when a group of educated
intelligent men are debating the results of one of the most basic
engineering axioms. Also amazing is that so many people rush to proclaim
a
known fact.......on a national stage............when they are exactly
wrong.

I wonder how this thread would play out in Japan, or Germany?