What was the knot line and float used for?

The knot line was a type of rope used for measuring speeds in sailing races. It was used before timing devices had been created. The knot line had five knots and was attached to the deck of the ship over a pulley and was led along the side of the ship at the water level while the ship was on course. The knots would pass through a person's hand and the number of knots would be counted during a 30-second period so that the speed could be calculated.

The Float

A float was created to ensure an accurate speed could be measured. The float was a 12ft pole attached to a line 49ft long. It was thrown into the water from a boat travelling forward at speed. The time taken for the boat to catch up with the float was then measured. The more knots, the faster the vessel traveled during the elapsed time.