How Does A Boat Speedometer Work

Nothing can match up to the fun of sunbathing on the deck of your boat while making the most of your summer escapades. Having a boat of your own makes thing much better as you get to enjoy the best of sea and sand whenever you fancy.

A speedometer serves as an extremely important instrument which can give you a clear idea of the speed level of your boat. Today we are going to discuss in brief about the working of your boat speedometer so that you can troubleshoot problems and utilize its efficiency to the fullest.

Speedometers rely on pilot tube mechanism which has led to its nomenclature of Pitometer. It compares your boat speed with that of the water on which it is moving. You can gain idea about accurate boat speed through the constant supply of two unique data pertaining to water speed and air pressure created by water.

A pilot tube which is connected with the system passes through the underside of the boat into the water. Water is pushed inside the hose as the boat glides along the surface. The speed is measured whenever water travels into the tube area through the pilot. The lack of any exit prevents water from getting into the hose. This causes a change in air pressure inside the hose as your boat moves at different speed levels.

The gauge can provide with an estimate of your boat speed by combining air pressure with water speed. The degree of pressure shares a positive correlation with water speed. A rise in air pressure induces the meter to reveal a faster speed. Similarly, low speed hints at decrease in air compression.

Boat speedometers can be broadly categorized into three categories for common use:

  • Using GPS or global satellite positioning to measure speed – this type of speedometer transmits periodic signals to orbiting satellites for obtaining the most accurate boat speed indications.
  • Using velocity and water pressure – it uses a tube within the hull for collecting information and measuring speed from the same.
  • Impeller is employed for gauging speed – it is positioned beneath the ship and follows the same principal as that of an anemometer while measuring wind speed. The impeller spins faster in sync with increasing speed of the boat to measure the vessel’s speed.

Bottom Line

Amongst the three types, the GPS method ranks highest in the scale of accuracy. Before the advent of these modern speedometers, a rope tied in knots at a specific distance from each other was used to be dropped in water. The number of knots which passed by over in a particular time frame provided with an accurate estimate of the speed of the vessel. This navigation method earned the name of dead reckoning and was the primary means of gauging nautical speed before the advent of modern instruments.