Underwater Exhaust Outlet Segmentation for Hull Noise Reduction
Solution Overview
Problem
Underwater propeller drives installed on a boat's hull bottom generate noise and vibrations when the engine is running in idle position due to exhaust gases rising and hitting the hull, existing solutions either create cavitation or do not effectively utilize water as a silencing medium.
Innovation Solution
A method that controls exhaust gas exit by using a second underwater exhaust outlet closer to the hull bottom when the engine is running and the transmission is in neutral, which can be achieved through a rotatable housing or a valve system, allowing gases to exit through non-coinciding openings, thereby reducing noise and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If exhaust gases are discharged through a single underwater outlet positioned for optimal silencing, then noise reduction is improved, but exhaust backpressure increases during idle operation causing gases to hit the hull bottom
Solution Approach 1:
The exhaust discharge system is segmented into multiple outlets (first and second underwater exhaust outlets) positioned at different locations. The first outlet is positioned for optimal silencing effect, while the second outlet is positioned to prevent gases from hitting the hull bottom during idle operation, allowing the system to divide the exhaust flow management function across multiple discrete discharge points
Solution Approach 2:
The system dynamically switches between different exhaust outlet configurations based on operational conditions. A control unit activates the second underwater exhaust outlet specifically during idle operation when the transmission is in neutral position, creating a dynamic adaptation of the exhaust system to different operating states rather than using a fixed single-outlet configuration
2Object-affected harmful factors
If a second auxiliary exhaust outlet is added to prevent gases from hitting the hull, then noise and vibrations are reduced, but the system complexity increases
Solution Approach 1:
The second underwater exhaust outlet serves multiple functions: it prevents exhaust gases from hitting the hull bottom during idle operation, reduces noise and vibrations, and works in conjunction with the first outlet during other operating conditions. This multi-functionality justifies the added complexity by providing several benefits from a single additional component
Solution Approach 2:
The control unit automatically manages the activation of the second exhaust outlet based on detected operating conditions (idle position with engine running), making the system self-regulating without requiring manual intervention. The system serves itself by automatically adapting the exhaust configuration to the current operational state
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly reduces or eliminates noise and vibrations caused by exhaust gases when the engine is running in idle position by directing gases away from the hull, enhancing comfort and quietness.
Implementation Method 1
utilize the water as a silencing medium
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
A method for controlling the exit of exhaust gases from an engine which is used to power an underwater propeller drive arranged at the hull bottom (105) of a boat. The method comprises letting the exhaust gases flow from the engine through an exhaust channel (110) and exit through a first underwater exhaust outlet (115) in the underwater propeller drive. According to the method, if the engine is running and the transmission of the propeller drive is in neutral position, a second underwater exhaust outlet (220; 50, 60) is opened for letting exhaust gases in said exhaust channel exit (110) in a position closer to the hull bottom (105) of the boat than the first underwater exhaust outlet (115).