Page MenuHomeFeedback Tracker

Boat - Prop gets out of the water, engine breaks + sound off
Reviewed, LowPublic


If you are going with a boat fast over waves, and the propeller gets out of the water, the engine breaks and the engine sound is going off. that is not very realistic! Should be fixed.


Legacy ID
Game Physics
Steps To Reproduce

Go fast with a boat over waves.

Event Timeline

red2blue edited Steps To Reproduce. (Show Details)Mar 6 2013, 1:15 PM
red2blue edited Additional Information. (Show Details)
red2blue set Category to Game Physics.
red2blue set Reproducibility to Always.
red2blue set Severity to Minor.
red2blue set Resolution to Open.
red2blue set Legacy ID to 2379355540.May 7 2016, 10:55 AM
Thales added a subscriber: Thales.May 7 2016, 10:55 AM

Please let us know in note section if you are still able to reproduce this issue in latest Developement build.

The "Problem" is still the same.
If you turn the waves to max, and you take the rescue boat and drive over the waves, the motors rpm goes down as long the propeller is out of the water. This seems to be unrealistic for me. You don't reduce the rpm every time the propeller goes out of water. I could be wrong, but that is my opinion :-)

This issue was processed by our team and will be looked into. We thank you for your feedback.

b101uk added a subscriber: b101uk.May 7 2016, 10:55 AM

When you get cavitation or the propeller suddenly coming out of the water when it was under high load on an engine without a hard governor, it can lead to engines detonating, in addition with 2-strokes it can cause leaning of the fuel/air mixture thus the lubrication is reduced at the same time RPM rise much increasing the risk of seizure which is further compounded by the raw-water pump sucking air into the cooling circuit of the engine (water from the sea/river/lake acts as the cooling medium pumped around the engine), also in the case of cavitation either on water jet propulsion units or conventional screw props it can actually start to abrade the metal from the blade tips and their leading edge, as small area of water near the tips/leading edge actually vaporises causing small vapour bubbles which then suddenly collapse due to the pressure change which can cause localised point pressures of up to 60000psig (4137 bar) on the propeller blade surface, when abrading starts to damage the tips/leading edge this only serves to cause yet more cavitation, in extreme cases cavitation can destroy a propeller in minutes – e.g. repeatedly lifting out and lowering back into the water an outboard motor propeller at maximum rpm.

That is why off-shore power boats used for racing actually have a guy who’s only job is to work the throttles and adjust the trim tabs to help keep the propellers in the water and to back-off the throttles when they do come out of the water, in order to protect the engines and minimise cavitation when they renter the water.

Throttleman doing their job:

So the principle of getting engine damage of high performance 2-stroke or 4-stroke engine (outboard motor) is not itself incorrect OR likewise having to reduce throttle when out of the water is also not incorrect, the automotive equivalent of not having your propeller in the water is like having your drive wheels off the ground.

However the problem in the game with the RHIBs, is that their centre of gravity is in the wrong place when under power, meaning that the front of the RHIB is dropping over the wave sooner than it should thus lifting the rear out of the water, when in reality the centre of gravity (fulcrum) is much further back and in essence moves with power and speed changes, given if you are pushing water backwards to generate forwards speed then there must be an equal force being pushed forwards from the propeller centre beneath the fulcrum which also wants to push the back of the boat down and conversely lift the front up as they rotate around the fulcrum.

So in essence the RHIBs need a dynamic fulcrum point which moves backwards with power application and speed (it still needs to be further back than it is at the moment), this then would allow them to be stationery and act much as they do now while at the same time when under power it would shift to the rear.

Also what doesn’t help I think, is you sea waves are to close together which is only serving to create steeper waves with a more pointed top, when you could probably move the waves twice the distance apart and marginally make the troughs between the wave tops slightly lower ending up with waves with less steep sides and a wider top and marginally taller which would reduce somewhat the rear of the RHIBs lifting out of the water.