In article W9wEb.426354$275.1302314@attbi_s53, Greg Milligan
wrote:

I'm interested in a plans-built amphib, and the Coot and Osprey II have
attracted my attention. Any thoughts/opinions about one vs the other?

A friend of mine built an Osprey II twenty years ago with a 160 HP fuel
injected O-320. He could never get it on the water without porpoising.
Another fellow 30 miles away built one 15 years ago and extended the
step six inches further aft from what the plans called for. This
enabled him to land and take off without porpoising.
I flew the one my friend built for twenty hours. Including a trip to
Oshkosh and back. Land and take off at 85 kts. Cruise at 95-100 kts.
Max speed 110 kts. Good rudder authority, poor aileron authority in
cross wind conditions. I'm 6'3" and had to scrunch down in the seat to
keep my headset from contacting the side of the fuselage. Gear up
landings on wet grass are non events with the fuselage keel and wing
sponsons. I was the only person (other than him) that he let solo it.
It was fun to fly, but because of the difficulty he had on water, I
didn't try to get it wet.

On a related issue, I have been underwhelmed by the useful loads of both
aircraft...around 450 pounds, more or less. Is there any "conventional
wisdom" out there about "supersizing" a plane; i.e. building to 120% or so
of scale?

TIA.