peterivanac
Member
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After watching the Paul Larsen Interview, I am surprised by the apparent lack of clarity around the behaviour of the main foil. I was communicating with Paul during the record period and as someone who designed, manufactured and tested super-cavitating foils in the form of propellers on a regular basis, I felt that we gave a pretty clear opinion and explanation of the current foils and what design features/conditions were required to obtain maximum foil L/D for that application. We also provided foil sections and a recommended foil area for the application but cannot see if they were used (it doesn't look like it). We identified that the original super-cavitating foil had at least twice the area that was required and hence why they didn't trip the foil into full super-cavitation. Even after sawing off a good portion of the foil, there was too much wrong with the design to show significant gains. A new foil was recommended and you see the results. Whilst Paul didn't ever confirm the section shape and surface area they settled on, it did always appear that the final foil was still larger and had a flatter face section than our recommendations.
From the interview, it sounded like he did have a LOT of people in his circle of influencers so it can certainly be understood that there was some conflict about the design direction to take and how the foil should actually operate.
The fact is that the aim with these foils is to FULLY SUPERCAVITATE the low pressure side of the foil (not just the trailing edge) whilst minimising the angle of attack for maximum efficiency. To do this, I use quite a lot of camber near the trailing edge to generate lift. Another fallacy about these propellers is that you rely on surface ventilation at the design operating point. You do not. Ventilation is ONLY used to reduce both lift and drag during acceleration and trip the foil into partial super-cavitation at lower speeds/loads.
Based on the fact that Paul had to fiddle with fences to maximise the ventilation of the foil says to me that the foil area was still too high to naturally push the foil section into full super-cavitation on its own and the foil still may not have been fully ventilated on the record runs.
Other points of clarification;
- The super-cavity is comprised of water vapour (steam at ocean temperature).
- Maximum efficiency of super-cavitating foils requires a FULLY super-cavitating suction face.
- 100% foil super-cavitation can be achieved without ventilation (however is often required to get the foil to it's full loaded design point)
- The thickness of the trailing edge has NO affect on efficiency on a fully super-cavitating section at it's design point. It can however assist the propagation of ventilation which allows more foil slip which can assist the accelleration and loading of the foil to allow the formation of the super-cavity.
- Foil area is by far the most critical factor, followed by foil section and foil shape.
- Foil aspect is the least most critical factor on super-cavitating foils (within reason.
- There is no hydrodynamic limit to the operation of super-cavitating foil, only structural.
Based on what I have heard and seen on this video, I'm convinced that a new foil could further improve the efficiency of the foil and significantly increase the top speed. That fact that the boat did what it did shows just how right Paul got the concept and despite a possible lack of clarity around the operation of the foil, fully deserves all the credit for the project.
<iframe width="672" height="378" src="https://www.youtube.com/embed/uJ_A9-ddNKU" title="Shooting the Breeze with Ronstan - Paul Larsen" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>
From the interview, it sounded like he did have a LOT of people in his circle of influencers so it can certainly be understood that there was some conflict about the design direction to take and how the foil should actually operate.
The fact is that the aim with these foils is to FULLY SUPERCAVITATE the low pressure side of the foil (not just the trailing edge) whilst minimising the angle of attack for maximum efficiency. To do this, I use quite a lot of camber near the trailing edge to generate lift. Another fallacy about these propellers is that you rely on surface ventilation at the design operating point. You do not. Ventilation is ONLY used to reduce both lift and drag during acceleration and trip the foil into partial super-cavitation at lower speeds/loads.
Based on the fact that Paul had to fiddle with fences to maximise the ventilation of the foil says to me that the foil area was still too high to naturally push the foil section into full super-cavitation on its own and the foil still may not have been fully ventilated on the record runs.
Other points of clarification;
- The super-cavity is comprised of water vapour (steam at ocean temperature).
- Maximum efficiency of super-cavitating foils requires a FULLY super-cavitating suction face.
- 100% foil super-cavitation can be achieved without ventilation (however is often required to get the foil to it's full loaded design point)
- The thickness of the trailing edge has NO affect on efficiency on a fully super-cavitating section at it's design point. It can however assist the propagation of ventilation which allows more foil slip which can assist the accelleration and loading of the foil to allow the formation of the super-cavity.
- Foil area is by far the most critical factor, followed by foil section and foil shape.
- Foil aspect is the least most critical factor on super-cavitating foils (within reason.
- There is no hydrodynamic limit to the operation of super-cavitating foil, only structural.
Based on what I have heard and seen on this video, I'm convinced that a new foil could further improve the efficiency of the foil and significantly increase the top speed. That fact that the boat did what it did shows just how right Paul got the concept and despite a possible lack of clarity around the operation of the foil, fully deserves all the credit for the project.
<iframe width="672" height="378" src="https://www.youtube.com/embed/uJ_A9-ddNKU" title="Shooting the Breeze with Ronstan - Paul Larsen" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>
