Calculate the total frictional resistance of a yacht

Group of sailing yachts at race

The frictional resistance is a force that is generated when the underwater parts of the boat and the water around are in relative movement (the boat moves through the water, or, in other words, the water passes down the boat). Therefore, it is a hydrodynamic force, and as a resistance, it works in the opposite direction to the movement, trying to slow the boat down.

The frictional resistance is due to the energy lost by the boat in overcoming the forces that tie together the molecules of water surrounding the hull and its appendages and in creating the eddies that are left behind. This phenomenon happens in the boundary layer.



Fill in each input with the appropriate value:



You will find the results in this section after launching the calculation.


How to use this calculation template?

1- Fill in the input parameters

Hull parameters (for more information, please check “Introducing the hull“):

  • Length of waterline (LWL) in meters.
  • Beam of waterline (BWL) in meters.
  • Draft of the hull (TC) in meters.
  • Volume displacement of the hull () in cubic meters.
  • Prismatic coefficient (CP) (adimensional).

Keel parameters (for more information, please check “Hull appendages, planforms, and wind sections: what are they?“):

  • Draft of the keel (TK) in meters.
  • Root (top) chord of the keel (CK1) in meters.
  • Tip (bottom) chord of the keel (CK2) in meters.

Rudder parameters (for more information, please check “Hull appendages, planforms, and wind sections: what are they?“):

  • Draft of the rudder (TR) in meters.
  • Root (top) chord of the rudder (CR1) in meters.
  • Tip (bottom) chord of the rudder (CR2) in meters.
  • Number of rudders.

Fill in the input fields with the appropriate values before launching the calculation. The units to use in each input are written in brackets (e.g., [m]):

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2- Launch the calculation

At the bottom of the input fields, you will find the following three buttons:

  • Reset: deletes all the values of the input fields.
  • Example: fills the inputs with predetermined values based on the YD41 design of the book “Principles of yacht design. “
  • Calculate: launches the calculation.

We evaluate the validity of the input values after launching the calculation. In case errors are detected, they are displayed on the screen:

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3- Visualize the results

We calculate the frictional resistance for different boat speeds. The relationship between both the resistance and the velocity of the boat is then presented for convenience in various interactive charts and tables. All of them display the same results, sometimes from different perspectives. You can switch between them and choose the visualization that might be more convenient for you:

Line chart
Line chart
Doughnut chart
Doughnut chart
Bar chart
Bar chart

Both the doughnut and the bar chart also feature an alternative visualization: the half doughnut and the aggregated bar chart:

Half doughnut chart
Half doughnut chart
Bar chart
Aggregated bar chart

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4- Interact

Use the selectors located at the top left of the results area to switch between the different visualizations available:

Line selector Line chart selector

Doughnut selector Doughnut chart selector

Bar selector Bar chart selector

Table selector Table selector

The frictional resistance value can be displayed either in Newtons (which is a unit of force) or in a percentage representing the ratio between the resistance generated and the hull displacement. You can change between both options with the appropriate selector:

Newtons selector

The boat speed axis can display either Knots, meters per second (m/s), or Froude Number (Froude):

Speed selector

The results are calculated for different angles of heel. You can select the heel angle for which you want to display the results:

Change the doughnut chart from full to half doughnut with the following selector:

Change the bar chart to an aggregated bar chart with the following selector:

Deselect or select the results related to each subcomponent by clicking or unclicking the following selectors, which appear at the top of each chart:

A tooltip with the results will appear on the screen when the mouse hovers over (in desktops and laptops), or the finger touches on (in mobile and touchable screens) the calculation points or specific areas of the charts:

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