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Enhanced Water Physics, Vehicle Seats Support Rear Propellers

September 25, 2012

by Kevin He


ROBLOX BoatingWe’ve talked previously about our ongoing effort to build robust joints and motors, and even touched on implementing seats for boats that support rear propellers. We’re still ironing out bugs with our soon-to-be released robust joints and motors, but we decided to release our new boat seat and water propeller support first. These features function independently, letting you experiment with propellers and watercraft today. Though this blog post features some pretty complex ideas in terms of building, we are hard at work on streamlining these building methods in the future so they’re intuitive for all uses. For now, check out what we’ve got so far.

In order to understand the changes we’ve made to ROBLOX’s water physics, let’s discuss how a propeller works, particularly in water. Like tires on a car, propellers convert power into forward motion by rapidly spinning at just the right speed, velocity, and most importantly, angle. The faster they spin, the faster your water-based vehicle should propel forward.

Typically a propeller is found on the rear side of the watercraft. With some of the new features bundled into our new water physics simulation, you can utilize an advanced water viscosity force that supports propellers. Previously, our vehicles featured seats that only detected side wheels (like those of a car). Now, vehicles can detect thrust from a wide range of angles, including the rear.

In order to use the BoatSeat script, keep in mind that the propeller must be mounted as a motor instead of a hinge; only then will the boat seat script take over control of the wheels.

The “boat seats” aren’t new—they’re an addition to our existing vehicle seat object — but their capabilities are. Our seats now feature scripts that allow you to tune the parameters of your propeller, including thrust and steer ratios. You can set a max speed, tweak the amount of torque your propellers generate, and customize the speed (which you can see with our brand new, easy-to-look-at speedometer) at which you can turn your boat by utilizing real life rules of physics (i.e. the thrust ratio is used to scale down the torque, the steer ratio is used to scale down the turning speed, etc.).

Giving users this amount of control could yield  incredible water-based machines, but leveraging real physics to build a boat that can cut through water may be confusing at first. Because a boat exists in a buoyant environment, many aspects of it don’t behave like the cars or motorcycles you may be used to driving on ROBLOX today. The steering polarity, for example, is reversed, meaning the steer ratio may need to go from a negative number to a positive one in order to properly maneuver your machine. It can be a bit complicated at first; that’s why we’ve made a place and a boat for users to start with.

ROBLOX Boat Level


This level features an open-water terrain and a  boat with customized propellers in order to serve two purposes.

  1. As a gamer, it’s really fun to drive high-speed boats through water.
  2. As a scripter or modeler, it’s a great opportunity to check out our boat seat scripts to see the numbers behind making a propeller actually work in ROBLOX (it’s trickier than you think), and experiment with tweaks and enhancements. If your boat becomes undrivable, remember, you can always go and grab another one with stock settings.

You can use the torque and turn speed properties to change the direction of the propellers spin

We’re looking forward to seeing what our users will create, and encourage you to post your creations to the ROBLOX Forum. We’ll be keeping an eye out for new watercraft in the coming weeks.