# Boat Propeller Water Physics - What am I doing wrong?

I’m working on a fun side project based on the classic Roblox personal build servers. One of my favorite things to do with the PBS tools was to create rocket ships, so I wanted to expand the tools to support custom cars and boats.

I got custom cars to work without a hitch, but for some reason I can’t get boat propellers to work no matter what I do. In the past, I’ve made a “build your own boat” game with basic building tools that revolved (no pun intended) around attaching a spinning hinged part to a floating boat, the rotation of which would move the boat forward.

However when building something that functionally appears quite similar to the working propeller boats of yore, I’ve been unable to get any movement. Are there specific properties I need to give the propellers, the boat or the Vehicle seat to make this setup work, or have there been changes to water physics such that this type of behavior is no longer supported?

The boat in question:

Responses from individuals familiar with water physics is appreciated. Please keep the replies free of unsubstantiated suggestions. Thanks!

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Seems like the problem is caused by the centers of the propellers being submerged. The closer the centers are to the surface, the less effective they are.

Doesn’t seem to move at all even with the propellers raised

It’s weird because I inserted a propeller boat free model that appears to be rigged the same way (plus-shaped plastic paddles on a wooden hull) that moves, but I can’t seem to figure out why this boat won’t.

Still no movement with a slightly streamlined design

I’ve been trying to get this to work for like a week now lol

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Does it have anything to do with its weight or possibly make it weightless?

So the problem happens when the center of mass of each blade is aligned with the axis of rotation. Because you’re using two intersecting blades, their centers are perfectly aligned:

`````` 2
1O1
2
``````

You could replace these with four blades:

`````` 3
1O2
4
``````

Two opposing blades will also work:

``1O2``
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I have seen this problem before, try instead of having 2 parts for each propeller, have 4 different parts for each of the blades of the propeller.

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I’m not sure what the problem might be. I just threw together a quick boat and it seems to work fine..

We’re probably doing it differently, though. I’m using a regular vehicle with some propellers on the back wheels.
Here is the file if you want it:
boat.rbxl (26.7 KB)

The issue here is that you are using 2 parts instead of 4.

The RotVelocity does not work in water, it only work with velocity.

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how do you even manage to do that, it seems so hard to code a literal part moving your boat
wait it’s not even coded, I never knew that parts can literally move through water

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