I have an 18ft narrow GRP cruiser and I find it very helpful to use a bollard in a narrow lock, especially when single-handing. Plastic cruisers start moving at the slightest surge much quicker than narrowboats, and you can look up from paddle-winding to find the boat moving away quite fast.
Controlling small GRP cruisers with the engine in a lock is hard - they are almost impossible to steer at low speeds. It's also nice to turn off the engine in a lock, particularly when it's a 2-stroke. Bollards just outside locks are also useful when single-handing: unless I can drive straight into the chamber, I usually tie up and switch off before the lock, get the boat through the lock on a centre (and sometimes bow) line, and only get back on board and restart the engine at the other end. In deep locks this also saves getting filthy climbing slimy lock chamber ladders. Rings would be just as good as bollards, if it's a question of aesthetics. Chris Hulin nc Lucy II at Bossoms
