New method of traveling on water

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Discussion Overview

The discussion revolves around a proposed method of traveling on water using Rotating Planing Surfaces (R.P.S.), which involve freely rotating disks designed to plane across the water's surface. Participants explore the lift-to-drag ratio, potential improvements over traditional planing hulls, and various experimental approaches to test the concept.

Discussion Character

  • Exploratory
  • Technical explanation
  • Experimental/applied
  • Debate/contested

Main Points Raised

  • One participant proposes that the lift/drag ratio of the rotating disks could exceed 5:1 due to reduced skin friction and differential fluid velocity compared to traditional planing surfaces.
  • Another suggests that practical experimentation, such as attaching the disks to water skis, could quickly reveal the effectiveness and control issues of the design.
  • A participant compares the design to a hydrofoil, noting that it may be more sensitive to surface waves and questioning the necessary boundary layer thickness for effective disk rotation.
  • Concerns are raised about the potential trade-off between reduced relative speed and induced drag, which could affect lift.
  • Suggestions for experimental setups include creating small models to measure drag forces under different conditions.
  • Some participants discuss the idea of powered rotation of the disks, with differing opinions on its necessity and benefits.
  • A participant references the Dunning–Kruger effect in response to perceived overconfidence in the discussion.

Areas of Agreement / Disagreement

Participants generally agree that experimentation is crucial to validate the proposed concept, but there are multiple competing views regarding the mechanics of the design, the implications of disk rotation, and the overall feasibility of the approach.

Contextual Notes

Limitations include uncertainties about the boundary layer dynamics, the effects of surface waves on performance, and the specific design parameters necessary for optimal functioning of the rotating disks.

Colin Wilson
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My question concerns what I call R.P.S. (Rotating Planing Surfaces). This version uses freely rotating disks to plane across the surface of the water somewhat similar to wheels on a car going down the road. Specifically what the lift / drag ratio might be and will it be higher than a typical planing hull at about a 5:1 ratio. My explanation of why I expect an improvement goes like this:

Since the disks rotate freely the skin friction is limited to the deflection of the boundary layer into a shallow arc from the front of the planing edge of the disk to the back of the planing edge of the disk. This results in an average differential in velocity between the planing surface of the disk and the water that is much lower than a non-rotating planing surface such as a planing hull or a lifting surface such as a hydrofoil would experience traveling at the same speed.

The following illustrations show the disks (attached hull not shown) with about 15% of the bottom surface area submerged. The attack angle of 5 degrees and the deadrise angle of 15 degrees being typical of a planing hull at speed.

Front view
Disks with WL front.jpg


Side view

Disks with WL side.jpg

Bottom view submerged area in orange
Disks with WL bottom.jpg
 
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Take a pair of water skis and add a set of your planing disks. You will quickly find if it works, if there are any control issues, and if you need to try different geometry. This is a case where one experiment is better than 1000 opinions.
 
A hydrofoil flies with its foils submerged so it is not affected by small surface waves. Your design appears to be a hydroplane that skims on the surface, and so is more sensitive to surface waves.

The downward weight of the vessel is still imparted to the water, so the vessel will radiate the same energy as wave pattern, circulation and wake.

You have reduced the whetted area, and reduced the differential fluid velocity, but I wonder how thick the boundary layer will need to be if it is to drive free disk rotation. Without a differential velocity the disk will not spin. Should the disk be rough, dimpled or smooth?
 
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Welcome, Colin :cool:

Interesting idea!
I am not sure, but it seems to me that reducing the relative speed would reduce the desired lift also, which would lead to inceasing the induced drag.
 
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Thanks for your replies. I've attached a PDF to better explain the concept and (page 4) to answer your replies. I believe I would need test tank like results to be taken seriously (test bed page 3) but I'm retired now with limited resources. I thought of maybe a crowd funding project? Any suggestions.
 

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Thank you for posting that.
I like that RC boat. :cool:
 
Interesting idea. I agree that an experiment will be the best thing to see how this works. To make a experiment that is not so expensive you can make a small model, and get a small boat that you can drive at a constant speed. Then make a rig where you can pull the model a distance off the side of the boat (so the bow wave does not affect it) and make the disks on the model able be locked. then pull the model with a line and have a fishing scale or something like that to measure the difference in drag force with the disks locked and free rotating.
 
@Colin Wilson
You should also consider powered rotation of the disks.
 
Baluncore said:
@Colin Wilson
You should also consider powered rotation of the disks.
He needs another form of propulsion to get up planing on the wheels anyway so i don't think adding a second mode of propulsion for after it is up on a plane is of any benefit.
 
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Stormer said:
He needs another form of propulsion to get up planing on the wheels anyway so i don't think adding a second mode of propulsion for after it is up on a plane is of any benefit.
I am not suggesting it as a form of propulsion.
It may provide more lift from the area of disk contact, by breaking or separating coanda effect.
 
  • #11
Baluncore said:
I am not suggesting it as a form of propulsion.
It may provide more lift from the area of disk contact, by breaking or separating coanda effect.
Ok. Then i misunderstood. I thought it was for boundary layer propulsion.
 

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