Every ship has a certain hull speed. This can be useful to know. You can also easily calculate it yourself. We are happy to explain more about the advantages and disadvantages of hull speed and how to calculate it.

## What is hull speed?

Hull speed is the maximum speed at which a boat can sail in a normal condition. The hull speed is caused by the amount of water pushed away by the underwater ship (the hull). If the boat is sailing in normal condition (i.e. at hull speed), a bow wave is created in front of the bow of the ship. This is because the water is pushed away there and moved to the rear. If the high hull speed is exceeded, the boat will plane. In this case the boat no longer sails through the water, but over the water. The following image explains the different phases.

## Why know hull speed?

The hull speed therefore indicates how fast a boat can sail in a normal condition. This can be useful to know. If you continue to sail between low speed and hull speed, you will need significantly less power. This saves fuel and is therefore more sustainable. If you exceed the maximum hull speed, it will be difficult to gain more speed. Instead of speed, your boat only creates more waves. So it is better to avoid hull speed if you want to gain speed and planing.

## How do I calculate it?

Do you want to calculate the hull speed of your boat? Then you can use a simple calculation to calculate this. The sum is as follows: multiply the square root of the ship’s waterline in meters by 4.54. A 9 meter boat therefore has a hull speed of (√9=) 3 x 4.54 = 13 km/h. If you have a boat of 16 meters, the hull speed is 18 km/h. After all: (√16=) 4 x 4.54 = 18 km/h. Please note: this speed is purely an approximation, but it is a useful rule of thumb.

## The importance of hull speed

It can be important to calculate the hull speed of your boat. To sail fast, your boat’s power must be much higher to exceed the hull speed. The boat must ride over its own bow wave and lift out of the water. But once your boat has reached hull speed, it can hardly increase in speed. This is because the boat cannot catch up with its own bow wave, because it cannot travel faster than the running speed of the bow wave. In this case, adding more power only results in more water displacement. The hull speed is therefore a physical limitation of the sailing speed.

## Advantages and disadvantages of a high hull speed

Sailing at a high hull speed has both advantages and disadvantages. An advantage is that your boat requires considerably less power. This saves fuel and is therefore more sustainable. The disadvantage is that it is more difficult to increase speed. This is because the boat cannot ride over its own bow wave. Your boat is then ‘trapped’ in water displacement.