It can be the key to saving from danger in many situations regarding speed. You can view speed from different angles. In this article, we are talking about hull speed. If you are a fan of sailing, you need to know what hull speed means and how important it is when designing a boat or any other boat. This article will introduce you to the formula for calculating hull speed and how our calculator works.

What is hull speed?

Firstly, we need to introduce you to the meaning of this term. Hull speed refers to the speed at which a particular vessel with a displacement hull should travel so that the waterline is equal to the wavelength of the bow wave. A bow wave means a wave that forms on the bow of a vessel as it floats on water.

Hull speed measures the speed of a boat concerning its hull. This measure is a factor of the waterline obtained by calculating the hull’s speed while sailing. Two factors are important here, namely waves and wavelengths. Waves you create while a ship or boat is sailing need to move at the same speed as the vessel’s hull.

However, it is necessary to know that waves are created on the bow and stern when sailing, which gradually slows down after spreading from the hull. It is essential to keep the balance up to that point to change the wavelength, representing the distance of one wave tip. We can say that the ship or the boat travels at the speed of the hull when the wavelength reaches the level of the waterline.

Graphical view of Hull Speed
Graphical view of Hull Speed

Why does hull speed matter?

Knowing hull speed can help you answer the question of how fast a boat can go. This specific measure affects how quickly the ship can travel. During the voyage, you should synchronize the hull speed with the bow wave and stern wave speed. Interference can then occur, resulting in more efficient ship movement.

If your speed is higher than the hull’s speed, the “nose” of the vessel will rise for the ship to reach the bow wave in this way. This process is known as planning and requires a lot of energy. The more you try to increase the speed and move faster than the hull speed, the more thrust it needs. The speed is exercised as the tilt of the vessel moves upwards.

Shortcomings of hull speed

Like all other measures, this one has its drawbacks. The science behind the hull’s speed clearly shows us all the advantages of knowing this concept, but it is essential to point out that it all depends on the hull’s shape. The hull design can be crucial in the work and functioning of the hull speed. We can distinguish in practice hulls found on canoes, ships, boats, catamarans, or kayaks and each of them requires different specifications and adjustments to the waterline.

Hull speed formula

The formula you need to use to calculate the speed of the rate depends on the value of the length of the vessel’s waterline, which you can express in feet. The following mathematical expressions presented below we can use to accurately calculate the waterline to achieve the desired hull speed of your vessel:

V_{hull} = 1.34\cdot \sqrt{L_{waterline}}

Or

L_{waterline} = \left ( \frac{V_{hull}}{1.34} \right )^{2}

How to calculate hull speed?

There is a well-established rule that we adhere to when measuring hull speed, and that is the understanding of “displacement hull.” The bottom line is that it is the hull of a boat traveling through the water. In this process, a tremendous amount of water is squeezed out. We come to data that says that the speed achieved in a series of waves expressed in knots equals 1.34 square roots of the wavelength.

The velocity of the hull (in the knots) is equal to 1.34 multiplied by the square root of the wavelength (in feet). As the wavelengths increase and the waves become more significant, the value of the hull speed changes. For example, we will take the situation that you own a boat with a total length of 18 feet while the value of the size of the waterline is between 16 and 17 feet. Guided by the presented formula, the hull speed following these values is 6.5 mph.

Example of Hull Speed
Example of Hull Speed

Hull Speed Chart: knots, mph, and km/h

To have an insight into all the units in one place, we can use the table below:

Waterline length (in feet)Hull speed (in knots)Hull speed (in mph)Hull speed (in km/h)
83.84.47.0
94.04.77.4
104.34.98.0
114.55.28.3
124.75.48.7
134.95.69.1
145.05.89.3
155.26.09.6
Hull Speed Chart

How to use the hull speed calculator?

Calculating hull speed using our calculator is a straightforward concept. CalCon calculators are extraordinarily advanced and powerful tools that give you the results you want in no time. For the calculation, you only need one value: the value of the length of the vessel’s waterline. Entering this value will automatically show you the hull speed in the second provided field.

FAQ?

1. What happens if you exceed hull speed?

The process of exceeding the hull speed causes the vessel to climb along the rear of the bow wave, creating huge waves with strong resistance.

2. How to increase my boat’s hull speed without changing its hull?

An increase in hull speed without changes in the hull can occur if you overload your boat. Again, this is a displacement hull, which in most cases is much narrower at the bottom, and therefore if you apply enough pressure downwards, that weight will further lengthen the vessel’s waterline, which leads to an increase in hull speed.

3. Can a boat go faster than its hull speed?

There are no rules that say you can’t develop the speed of a ship or boat faster than the hull’s speed. This is very easy to achieve with certain vessels, and then when you exceed the speed limits, the wavelength will become longer than the length of your boat. The bottom line is that a more significant amount of power is required to achieve movement faster than hull speed.