Jim! Yes I’m in Sydney!
http://www.hobiecat.com/kayaks/features/miragedrive/ - this is one example… see the animation on the right hand side of the page…
The one I was originally talking about didn’t have a motion like this one…. It was shaped like the hydrofoil on an outboard motor’s cav plate… but as it moved downwards through the water it angled nose first downwards… and as it was dragged back up through the water it angled upwards and was pedal driven… so it just waved up and down underneath the kayak..
That mirage drive looks fancy… I wonder how much more efficient it is than a standard prop… I would imagine two of those drives… either on the sides of the hull or on top and below the main hull would negate any oscillation effects…
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of JimToddPsub@aol.com
Sent: Monday, 6 December 2010 2:50 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Fishtail propulsion
Stew, you're in New South Wales, aren't you?
Although I'm very healthy I certainly won't live long enough to fabricate every Rube Goldberg device that comes into my mind. Hopefully just conceptualizing some of them will teach me something that might actually be applicable and useful.
I think any biometric manned submersible would still have only one pressure hull for occupants. Any more than that would also have to include a large supply of sick sacks. Even with a single occupied hull you would have to devise a method to counteract the left and right motion to avoid motion sickness.
I know there is a commercially available kayak with a prop driven by a bicycle type mechanism. The shaft goes vertically right through the bottom of the kayak.
Ive seen kayak’s/canoe’s here with a pedal powered “fin” under the centre of the kayak… it moves up and down and angles itself as it moves so you get forwards propulsion! J it doesn’t have to be a sideways motion (dolphins and whales move their tails up and down not side to side J …. And if its on the centre line of the sub… dive planes could be automated to counter any up and down movement created by the fin’s drag in the water…
Thinking outside the box…. I know its hard (read impossible) to build flexible pressure proof joints… but in the future how about a flexible submarine? Like a snake… the centre portion could remain level, with occupants inside, and the other front and rear joints could create propulsion and manoeuvring… much like those autonomous snake robot’s! J a multi segmented sub… hydraulic rams between each section… you could even seal each section off from each other while under way… so each section is actually separate and then use the hydraulics to align the segments, seal them so you can walk from one end of the sub to the other when its not underway, or running off secondary propulsion… no flexible joints that way J
Stew
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Alan James
Sent: Friday, 3 December 2010 3:10 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Fishtail propulsion
I guess you'd need a large keel or rudder at the front of the canoe to stop the aforementioned
side to side movement, wich would be more pronounced being on top of the water.
----- Original Message -----
Sent: Friday, December 03, 2010 4:47 PM
Subject: Re: [PSUBS-MAILIST] Fishtail propulsion
It gets more complicated as you scale it up. As you wag the tail faster, the forces on the mechanism and structure get pretty big.
In addition to the propulsion from the sculling action, a significant portion of a fish's propulsion results from the vortices generated from the tail motion which is why they can accelerate so rapidly. It's similar to a whiplash action.
I may or may not be able to get the canoe to move more easily or conveniently than with a paddle. Or I might just make the yuloh master laugh.
I saw some others when I followed the link. One was hard to tell from the real thing.
Looking at their side to side head movement convinces me that it would be a bad
form of propulsion for a sub as you'd get sick quickly.
----- Original Message -----
Sent: Friday, December 03, 2010 3:41 PM
Subject: [PSUBS-MAILIST] Fishtail propulsion
Here are a few videos I found of mechanical fish such as we were discussing.
At some point just for fun, I might build a rig to try out on my canoe or a Jon boat. From a top view:
P= the powered section moved left and right
BBBBBBBBBBBBBBBBBBBBBBxPPPPPPxFFFFFFFF
When power is applied to P to swing it left and right, F will swing in the opposite direction (by the force of the water) to provide propulsion from the sculling motion. P will move through fewer degrees of arc than F. The range of motion for P is determined by the configuration of the push/pull rods which power it. The range of motion for F is determined by stops on the hinges.
I have several other projects with higher priority, but maybe one of these days...