[MarkofSeaLife]

I put a turn or 2 around the amidships cleat.

 

[MarkofSeaLife]

I still dont see why you want a knot in the middle at all. Unless you are only using the one dock, the position of the dock cleats/bollards etc will be different each time and you will never be exactly in between then. The knots look too long to adjust but just turned around the cleat its quickly and infinitely adjustable.

 

[MarkofSeaLife]

I dock the boat in a slip, not a T dock so the 40 ft double spring line which is tied off at the dock and a piling at the entrance to the slip is suspended in the air when not in use. I slide the boat into the slip, stop at about the right spot and go amidships to slip the double spring onto the midship cleat. If I am not in the exact right spot I use the spring to pull the boat slightly so I can slip the loop onto the cleat. Once done I shutdown the engine and leisurely tie off the remaining dock lines.

Ahhhhhhh. Right. OK you explained it a bit better

Maybe an alpine loop with a bit of hose as chafe guard where it goes around the cleat.

But over time any knot will tighten up and be difficult to remove.