We don't use many knots in the traditional manner. We normally splice loops into the end of our lines
The Eye Splice as they are very strong and permanent.
All of our floats are fitted with cleats at both ends. We generally secure lines to the aircraft using a cleat hitch
The Cleat Hitch.
We use an alpine butterfly on one of the fixed lines on our semi-sub to prevent the aircraft moving either forward or aft with a single rope whilst embarking and disembarking passengers.
If we are using someone elses mooring or picking up from a boat we will often tie a figure eight on the bight
Figure Eight on a Bight so that we can hook the loop over the back half of the forward cleat. We can then let the aircraft float back prior to starting the engine. When we start moving forward the loop falls off the back of the cleat - being attached to another boat/mooring prevents us from drifting into something expensive if the engine doesn't start.
The other knot we use is a bowline to secure the loose end of the anchor rode to the float locker to stop us from losing the anchor.
Rope selection and care is very important. Nylon is excellent as it is very strong and stretches under load. 12mm nylon has a breaking strain of 2940kg compared to only 1260kg for the same sized silver rope. Keep rope out of the sun, dry and away from chemicals to prevent deterioration.
A bare (web) footed pilot.