Buoyancy Feature
The Buoyancy Feature samples Unreal Water at spherical pontoons and applies flotation and water resistance to the simulated Assembly. A Part Model may contain only one Buoyancy Feature, but that feature can contain multiple pontoons.
The Unreal Engine Water plugin is required. A Watercraft Controller can command propulsion and attitude, but this feature produces the actual buoyancy and hydrodynamic resistance.
Add buoyancy
- Open a Part Model in the Part Model Editor.
- Add Buoyancy in the Features panel.
- Add pontoons from the Body in the Outliner, or use Buoyancy Auto Setup to generate an initial layout from Body mass.
- Position the pontoons across the hull and adjust their radius.
- Tune feature Settings while watching the Validation summary for supported mass and estimated immersion.
Auto Setup replaces existing pontoons. Its Pontoon Count, Target Immersion, and Layout Margin generate an initial layout and fit radius, height, and heave damping; review the result rather than treating it as final tuning.
Pontoon parameters
Each pontoon is a spherical water sample and force application point in Body-local space.
| Parameter | Description |
|---|---|
| Pontoon ID | Stable identifier unique within this Buoyancy Feature. It cannot be empty or duplicated. |
| Position | Center of the pontoon relative to the Part Body, in centimeters. Wider placement provides stronger roll and pitch stability. |
| Radius | Sphere radius in centimeters. A larger sphere displaces more water and can support more mass. Must be greater than zero. |
| Buoyancy Coefficient | Per-pontoon multiplier applied together with the feature-wide coefficient. Use it to redistribute support without resizing the pontoon. |
| Enabled | Includes or excludes this pontoon from water sampling and force calculation. |
Buoyancy settings
| Parameter | Description |
|---|---|
| Buoyancy Coefficient | Feature-wide multiplier for static buoyant force. It is multiplied by each pontoon's coefficient. |
| Heave Damping | Linear resistance against a pontoon's vertical velocity relative to water. It opposes both rising and sinking. |
| Heave Damping 2 | Quadratic vertical damping. It has more influence at high vertical speed. |
| Max Heave Damping Force | Absolute damping-force limit per pontoon, in Newtons. 0 disables heave damping. Runtime also limits combined damping so it cannot reverse vertical motion in one physics step. |
| Max Buoyant Force | Maximum buoyant force per pontoon, in Newtons. This caps the support produced by a fully submerged pontoon. |
| Slide Resistance | Resists horizontal sideways motion so the direction of travel follows hull yaw. 0 slides freely, 0.5 carves noticeably, and 1 behaves almost as if on rails. It works without water drag being enabled. |
| Apply Drag Forces In Water | Enables body-wide linear and angular water drag while at least one pontoon is in water. |
| Drag Coefficient | Linear horizontal drag strength when water drag is enabled. |
| Drag Coefficient 2 | Quadratic horizontal drag strength, with more effect at high speed. |
| Angular Drag Coefficient | Resistance against body angular velocity while water drag is enabled. |
| Max Drag Speed Meters Per Second | Speed used to cap the linear and quadratic drag calculation. It limits drag growth; it is not a hard vehicle speed limit. |
Placement and tuning
- Spread pontoons toward the corners of the hull for passive roll and pitch stability.
- Place their expected waterline through the sphere rather than far above or below it.
- Match total support to Body mass before tuning damping.
- Increase Heave Damping if the hull bobs repeatedly; use the force limit to avoid harsh impulses.
- Increase Slide Resistance when the hull rotates but its velocity continues sideways.
- Enable water drag only when broader linear and angular resistance is needed.
Tune the Buoyancy Feature before the Watercraft Controller. Controller stabilization can hide poor pontoon placement, and excessive damping can fight the Controller.