First trial of horizontal fin drive

[Skip Johnson]

Good questions, not many answers yet.

The ultimate goal is to have enough information/data to make a rational decision in deciding which path to choose for a run at the 24 hour distance record.

On the one hand I believe the horizontal fin drive has the potential to be more efficient than the paddle drives currently in use. On the other hand the paddle drives are a proven more mature tech.
The way I've chosen to check this out in to try the idea in model form; build and trial out a model with a fin drive and then if it looks good enough trial against the paddle driven craft.
Originally planned to do it with two different craft but free running models guaranteed to not run in a straight line so I've gone to radio control.

My previous experience with RC was 50+ years ago, things have changed some, it's a fairly extensive rabbit hole ;-)
Initially just an inexpensive Xmtr/receiver/ servo used some existing nimh AA batteries. System was wonky and would lock up full left. Nimh batteries with high internal resistance was the problem. Initial trials also showed that operating craft and getting reliable data solo wasn't that easy for an old man so I've ordered a onboard gps module along with the proper batteries.

If and when the model looks feasible, I'll pull the fin drive (6-3mm screws) and replace it with a paddle drive with same motor, total weight and trim and see what happens.

The current variables to test are fin area, aspect ratio, angle of attack, and what ever shows up as something to consider. In the end whichever system goes the fastest with the supplied power is the route I'll recommend.

 

[Doug Halsey]

...
On the one hand I believe the horizontal fin drive has the potential to be more efficient than the paddle drives currently in use. On the other hand the paddle drives are a proven more mature tech.

Pump foiler technology seems to have matured nicely by now. Anything to be learned from them?

 

[Skip Johnson]

Quite a bit, the issue is the pump foilers are using foils for support and the forward drive is somewhat an ancillary thing.
My world revolves mainly around providing canoe designs that are optimized for minimum drag for a given displacement and speed range; this effort is an ancillary attempt to provide the most force with the least effort at the upper end of that speed range.

Their foils are asymmetrical whereas I currently think that the fin drive wants to be symmetrical, we'll see.

 

[fallguy]

Pump foiler technology seems to have matured nicely by now. Anything to be learned from them?

I wish my 5 ton boat could skate like that!

 

[SolGato]

I wish my 5 ton boat could skate like that!

You don’t need full foiling, you could gain a lot by incorporating foil assist to your Cat which has proven benefits like quicker planing, ride smoothing, faster top speeds and increased fuel efficiency.

On the high end there are big name power cat manufacturers using this technology for the above benefits, and on the low end pontoon boaters who are installing simple inexpensive bolt on kits and seeing good results.

Keep in mind with respect to the above pump foiling that while it looks easy, it is not.

It’s kinda like hula hooping.

At least with pedal power people who can ride a bike or stair step pick it up quickly.

I watch people spend hours and seasons on the water trying to master pump foiling starting out with different size foils and boards, working their way up the ladder. Some get it eventually, and some don’t.

A kite really helps, but then that introduces a pat head while rubbing belly kind of challenge.

And then there’s the E-Foilers, the new Jetski any clown can figure out after a few lessons and barely master and control before hitting the water at high speed using mooring fields as obstacle and race courses…

 

[fallguy]

You don’t need full foiling, you could gain a lot by incorporating foil assist to your Cat which has proven benefits like quicker planing, ride smoothing, faster top speeds and increased fuel efficiency.

On the high end there are big name power cat manufacturers using this technology for the above benefits, and on the low end pontoon boaters who are installing simple inexpensive bolt on kits and seeing good results.

Keep in mind with respect to the above pump foiling that while it looks easy, it is not.

It’s kinda like hula hooping.

At least with pedal power people who can ride a bike or stair step pick it up quickly.

I watch people spend hours and seasons on the water trying to master pump foiling starting out with different size foils and boards, working their way up the ladder. Some get it eventually, and some don’t.

A kite really helps, but then that introduces a pat head while rubbing belly kind of challenge.

And then there’s the E-Foilers, the new Jetski any clown can figure out after a few lessons and barely master and control before hitting the water at high speed using mooring fields as obstacle and race courses…

My boat has beaching keels and sacrificial timbers that it tries to skate up onto, but their design and lead in is mucho drag. I don’t want to steal any more real estate from Skip here. His project is really cool.

 

[jehardiman]

On the one hand I believe the horizontal fin drive has the potential to be more efficient than the paddle drives currently in use.

They are...sorta...kinda.... Depends on what you mean by "efficient". Today there are things like the pump foilers mentioned above, Suntory Mermaid II et. al., and wave powered sensor drones. These things use no power except their mass and waterplane. They extract energy from the wave orbital (and yes pumping up and down is/makes a wave) and use it to move in the direction that they want. Technically they are a facet if things called Wave Devouring Propulsion (WDP) or Wave Power Generators (WPG); they take in a portion of the wave energy as it moves past them. And that is the important point; oars/paddles, paddle wheels, and WDP all interact with the wave surface velocity/orbital in different ways. The same is not true for the screw propeller which for efficiency typically runs well submerged with its plane of action always perpendicular to the wave orbitals. Now this may not fit the rules and the river conditions of the MR340, but it is the reason the screw propeller replaced paddle wheels for most applications since the 1845 tug-of-war competition between HMS Rattler and HMS Alecto.

 

[fallguy]

Skip, the tuna uses a propulsion system that doesn’t rely on its body much. Your fins that failed were perhaps too flimsy as built? Not sure those bottom two are really tuna shapes either. Of course, the tuna are big eaters and may not possess the most efficient fins at all! Still really neat. It looks like your drive system has the fin running laterally, which of course forces me to ask if you tried to model a dolphin tail or why not?

And is the connection rigid or is the propulsion from each stroke. The dolphin wins in both directions.

Sorry if I am a pest, just curious, Dan.

 

[Skip Johnson]

Skip, the tuna uses a propulsion system that doesn’t rely on its body much. Your fins that failed were perhaps too flimsy as built? Not sure those bottom two are really tuna shapes either. Of course, the tuna are big eaters and may not possess the most efficient fins at all! Still really neat. It looks like your drive system has the fin running laterally, which of course forces me to ask if you tried to model a dolphin tail or why not?

And is the connection rigid or is the propulsion from each stroke. The dolphin wins in both directions.

Sorry if I am a pest, just curious, Dan.

First setup failed miserably; no forward thrust at all; my old mind doesn't see things as clearly as it once did. I thought I'd found a way way to have a fin oscillate without any mechanism in the water. Second setup worked reasonably well; current third seems good enough to establish some ground rules.

They are...sorta...kinda.... Depends on what you mean by "efficient". Today there are things like the pump foilers mentioned above, Suntory Mermaid II et. al., and wave powered sensor drones. These things use no power except their mass and waterplane. They extract energy from the wave orbital (and yes pumping up and down is/makes a wave) and use it to move in the direction that they want. Technically they are a facet if things called Wave Devouring Propulsion (WDP) or Wave Power Generators (WPG); they take in a portion of the wave energy as it moves past them. And that is the important point; oars/paddles, paddle wheels, and WDP all interact with the wave surface velocity/orbital in different ways. The same is not true for the screw propeller which for efficiency typically runs well submerged with its plane of action always perpendicular to the wave orbitals. Now this may not fit the rules and the river conditions of the MR340, but it is the reason the screw propeller replaced paddle wheels for most applications since the 1845 tug-of-war competition between HMS Rattler and HMS Alecto.

Efficient in this case is getting the most thrust from a fixed small power source; human power. Originally for a run at the 24 distance record. I suspect it might also be a good choice for the R2AK crowd moving large craft slowly but steadily, prop setups have been problimatical.

The fin drive, if it becomes viable isn't much use for marathon racing, Murphy watches over such things with interest.

A lot of this is rooted in past experience with noticing how Orcas performed in captivity and my experience with the slow improvement of AD style sculls as my builds got better over time.

 

[mc_rash]

Can you post more information preferably with a sketch or something on your setup? Others might make suggestions on it and help you refine it

 

[Skip Johnson]

Can you post more information preferably with a sketch or something on your setup? Others might make suggestions on it and help you refine it

Here's the current mark3 built primarily from laminated pieces of 3mm FRP held together with 2 and 3mm screws.

If there's a mark4 it will probably incorporate ball bearing(s) and some 3D printed bits and have adjustments for range of motion and spring tension.



.

 

[jehardiman]

Well I see a large part of your problem right there. The foil when oscillating needs a positive angle of attack throughout the stroke. With a passive spring, the vertical forces force the foil into that situation only in a small portion of the stroke. There are simple ways to fix that and even remove the need for the spring assembly at the base of the strut. Take a look at this paper:

Oscillating foils of high propulsive efficiency

Thrust-producing harmonically oscillating foils are studied through force and power measurements, as well as visualization data, to classify the principal characteristics of the flow around and in the wake of the foil. Visualization data are obtained using digital particle image velocimetry at...

dspace.mit.edu

EDIT to add; I don't know how much machine design you have had, but it is fairly simple to get the foil AoA step phased to the rotary cycle of the strut.

 

[Skip Johnson]

Well I see a large part of your problem right there. The foil when oscillating needs a positive angle of attack throughout the stroke. With a passive spring, the vertical forces force the foil into that situation only in a small portion of the stroke. There are simple ways to fix that and even remove the need for the spring assembly at the base of the strut. Take a look at this paper:

Oscillating foils of high propulsive efficiency

Thrust-producing harmonically oscillating foils are studied through force and power measurements, as well as visualization data, to classify the principal characteristics of the flow around and in the wake of the foil. Visualization data are obtained using digital particle image velocimetry at...

dspace.mit.edu

EDIT to add; I don't know how much machine design you have had, but it is fairly simple to get the foil AoA step phased to the rotary cycle of the strut.

The spring was a carryover from Harry Bryan's Thistle where it recovered some energy at the end of a stroke. It's already apparent it's not necessary here and spring tension is very light to center the foil when coasting to balance the weight of the foil. And yes it may not be necessary.

I really appreciate the link, have downloaded it and will try to digest it in the next few days.

My mechanical skills are rudimentary, if they had been better then my original high volume peddle powered jet might have been light enough that I would have finished the race ;-) More fundamentally I'm committed to keeping things as simple as possible, this thing already has 3 moving parts plus the motor crank. Since getting a 3D printer I've spent a great deal of time, filament and effort to make a simple morphing kinetic structure. While travelling down a different path about rattlebacks Rattleback - Wikipedia https://en.wikipedia.org/wiki/Rattleback I made a made a two sided version that is simple, elegant and has only one moving part, the rattleback itself. My drive to make a kinetic sculpture has subsided.

 

[fallguy]

Commenting much is outta my wheelhouse, Skip. But I have curious questions.

Do you have any idea what the angle of attack is and whether the angle is greater by far than the simple angle of the system?

Is the spring’s primary role to retain the fin holder?

Have you been able to measure the angle of attack delta from typical positions?

If the foil is mostly stiff, then is it just a paddle?

 

[Skip Johnson]

To satisfy some of your curiosity.

Current setup the foil operates at about 8 degrees +/- angle of attack, after digesting some of the info that @jehardiman kindly provided a link to, it should be more.

Spring's primary function is to keep the fin centered when coasting and might provide some transitional energy recovery at the top and bottom of strokes.

No; too early in the game.

Not a paddle, it's oriented 90 degrees +/- the angle of attack.

The last time I did some 2D video animation (parking jetliners @ an airport) the video was transferred to client on a floppy disk, not sure I could do such today, but this winter if I run out of things to do I might take a run at it.