Water Buoyancy Component in Unreal Engine | Unreal Engine 5.2 Documentation

The Water system includes a Blueprint Buoyancy Component which uses spheres (pontoons) to create a simplistic volumetric approximation of the object that is meant to interact with the water surface. This approximation provides a low-cost solution that can support multiple objects using buoyancy at the same time.

Example Water Buoyancy Blueprint

The Water plugin contains its own example content that you can use and explore. This includes a Blueprint which is set up using the Buoyancy component with a cube static mesh. In order for the cube to balance and sit upright on the water's surface, the Blueprint is set up using four pontoons.

The Buoyancy example Blueprint can be found under Engine > Plugins > Water Content > Blueprints and is named BP_BuoyancyExample. Drag and drop it above any Water Body surface. When you Play or Simulate, it will automatically drop and float along the water's surface like the example below.

Setting Up Water Buoyancy In A Blueprint

The following steps will show you how to set up and use your own Blueprint using a Buoyancy component.

In the Content Browser, create a new Blueprint Class, pick the Actor class, and give it a name. For this guide, we'll use "BuoyancyExampleBP."
Open your Blueprint. In the Components panel, click the Add + dropdown and select Static Mesh.
Select the Static Mesh Component. In the Details panel, assign a mesh to the Static Mesh assignment slot.

You can download the mesh used with this guide if you want to follow along exactly as shown. Drag and drop this mesh directly in to the Content Browser.

Boat Mesh
While still in the Details panel, enable Simulate Physics and the checkbox next to Mass (kg) under the Physics category.

Mass (kg) must be enabled for the Buoyancy Component to work.
In the Components panel, use the Add + drop down menu to add a Buoyancy Component.
Select the Buoyancy Component. In the Details panel under Buoyancy Data, you'll add some Pontoons that allow the mesh to float on water surfaces. Start by adding one Pontoon by clicking the Add (+) icon.

You should see a new pontoon element added to the array that looks like this:
Add three more Pontoons to the array for a total of four array elements. Place these pontoons along the front and back sides of the mesh to stabilize it on the water's surface, by using Relative Location to place the pontoons at the following locations:
- Index 0 (back left): 660, 370, 0
- Index 1 (back right): 660, -370, 0
- Index 2 (front left): -220, 370, 0
- Index 3 (back right): -220, -370, 0
  
  There is no visualization of the pontoons when entering their relative location. However, you can use Static Mesh Sockets and the Center Socket tag to place pontoons without entering specific location data, or add Scene components to your Blueprint and copy their location to the pontoon's relative location manually.
In the Blueprint Components panel, click and drag the StaticMesh component onto the DefaultSceneRoot making it the new Root component.

The Static Mesh must be the Root for the Buoyancy component to work properly.
Drag and drop your Buoyancy Blueprint into the level and place it above the surface of the water. Press Play or Simulate to see the results.

Buoyancy Component Properties

The Buoyancy Component has the following properties. These control the physics of how the pontoons interact with the surface of the water.

Click image for full size.

The following properties are available in the Blueprint Details panel under the Buoyancy section when you select the Buoyancy Component.

Property	Description
Pontoons	An array of available pontoons which can be of varying radii that are added to the component to approximate its volume. Center Socket: The socket on the Static Mesh to center this pontoon on. Relative Location: The location of the pontoon relative to the parent Actor's location. It is overridden by Center Socket when one is specified. Radius: The radial size of this pontoon (in world units). FXEnabled: Should this pontoon be considered as a candidate for visual/audio effects upon entering water for burst cues, which are implemented by the user?
Center Pontoons on COM	If enabled, center the pontoons around the center of mass when using relative locations. This is not used when pontoon locations are specified using sockets.
Buoyancy Coefficient	Increases the buoyant force applied to each pontoon.
Buoyancy Damp	A damping factor to scale damping based on Z velocity.
Buoyancy Damp 2	A second order damping factor to scale damping based on Z velocity.
Buoyancy Ramp Min Velocity	The minimum velocity to start applying a ramp to buoyancy.
Buoyancy Ramp Max Velocity	The maximum velocity up to which the buoyancy can ramp up.
Buoyancy Ramp Max	The maximum value that buoyancy can ramp to (at or beyond the max velocity).
Max Buoyant Force	The maximum buoyant force in the Up direction.
Water Shore Push Factor	The coefficient for nudging objects toward the shore (primarily for performance reasons).
Water Velocity Strength	The coefficient for applying force in River Water Bodies.
Max Water Force	The maximum push force that can be applied by River Water Bodies.
Apply Drag Forces in Water	Specifies whether to apply drag forces to an object moving through water.
Drag Coefficient	The coefficient for applying linear drag based on speed.
Drag Coefficient 2	The coefficient for applying linear drag based on the square of the speed.
Angular Drag Coefficient	The coefficient for applying angular drag that resists the rotation of the object.
Max Drag Speed	The maximum speed at which drag force is applied.
Apply River Forces	Specifies whether the engine should apply river forces such as downstream push and shore push.
River Pontoon Index	List of which Pontoons water forces should be calculated from. Used to calculate lateral push/pull, and to grab water velocity for main force calculations from downstream calculation when possible.
Water Shore Push Factor	The coefficient for nudging objects to the shore in Rivers (for performance reasons). Or, set negative to push towards the center of the river.
River Traversal Path Width	The path width along the inside of a river which the objects should traverse.
Max Shore Push Force	The maximum push force that can be applied by rivers towards the edge or center.
Water Velocity Strength	The coefficient for applying push force in rivers.
Max Water Force	The maximum push force that can be applied by rivers.
Always Allow Lateral Push	When enabled, allows an object to be pushed laterally regardless of the forward movement speed through the river.
Allow Current when Moving Fast Upstream	When enabled, it applies the current when moving at high speeds upstream. Disable for vehicles to have more control.
Apply Downstream Angular Rotation	When enabled, it applies torque to align the object along the downstream direction of the river.
Downstream Axis of Rotation	The axis with respect to the object with which the downstream angular rotation should be aligned.
Downstream Rotation Strength	The strength of the downstream angular rotation application.
Downstream Rotation Stiffness	The stiffness of the spring used to align the object along the downstream direction.
Downstream Rotation Angular Damping	The damping of the spring used to align the object along the downstream direction.
Downstream Max Acceleration	The maximum torque to apply per update for downstream rotation.

Debugging Water Buoyancy

You can debug the Buoyancy Component interactions with water surfaces using the console command r.Water.DebugBuoyancy 1. Each pontoon is drawn along with a grid of points that interact with the water surface.

The example below shows several different shapes and boat meshes using pontoons with different spacing and sizes.