My Potter 19 with trailer weighs between 1500 and 1600 lbs. We tow it with a
1995 Volkswagon Passat which has a V-6 engine, front wheel drive, and a 5
speed manual transmission. I've never determined the tongue weight, but
since both my wife (4'10", 100lbs) and I separately can lift it, I estimate
it at 50-80 lbs. That would put it between 3 and 5 percent of the towed
weight. We have no problems with swaying or any side to side motion unless
we go over about 65-70 mph. I wouldn't want to go much faster than that
anyway, and with a low tongue weight we have no trouble with steering or
with pulling the boat out on steep ramps.
I guess my feelings are that if you're satisfied with how things are
working, then there's no need to mess with anything like the 10% rule of
thumb.
Andy Krumpe
P19, Great Wight