Why not use it? Because on an unfamiliar boat and on many boats that some are very familiar with the knot meter is not accurate or reliable for anything. Glad it worked out for you. I would never suggest coaching anyone to rely on that boat tool/toy. The better coaching is to get and keep the head and eyes out of the boat. Note the relative movement through the water, past other fixed objects, and the closing on the mooring. One other hint is to keep everyone off the bow until the very last minute. The body(s) waiving boathooks and arms can be very distracting to the young helmsman in an unfamiliar space. If you have any doubt stop the boat well away from the mooring and then go ahead at the lowest possible headway possible with infrequent touches of forward gear to get and keep the boat moving with steerageway. That velocity will be different for each boat and wind condition. Practice bringing the bow to a mooring can be done at any time with no one on the bow. It should be done by any helmsman until the helmsman has confidence on the boat of the day.