# Schmidt Wave Propellor

Discussion in 'Boat Design' started by clmanges, Jul 23, 2008.

1. Joined: Jul 2008
Posts: 510
Likes: 102, Points: 43, Legacy Rep: 32
Location: Ohio

### clmangesSenior Member

I'm starting this thread as an exploration of drive systems based on winglike foils that move in relation to each other. I was going to take up this question in my other thread about a drive system for my rowboat (see thread "I'm new here" under Boat Design), but thought that this topic deserves its own thread.

The basis for my query here derives from papers by Kevin D. Jones:

http://aa.nps.edu/~jones/

and specifically,

You'll find elsewhere that research has been done on two-foil systems with a pure plunging motion of one foil (as compared to rotary), with a downstream stationary foil. And that's the departure point for this thread.

In the Schmidt system, the downstream foil is "passive" because it doesn't create its own flow pattern. (I know that "passive" is not exactly a correct term here, because the foil does produce thrust -- I think it's safe to call it "quasi-passive" for now; better definitions are always welcome.)

Now, what if both foils move? I can think of a number of possible configurations, but for now I'd like to look at pure plunging motion.
Let's start with the case of opposed plunging motion: one foil is going up while the other goes down; their motion is 180 degrees out of phase.

What kind of interaction results from this? Will it always produce a thrust pattern (a reverse Karman street)?

What think ye?

Curtis

2. Joined: Aug 2021
Posts: 16
Likes: 0, Points: 1
Location: Denver, CO, USA

### Horton HCCIJunior Member

Hi, Curtis--

I looked at some of your (very) old threads, and it seems we share some interests in very unconventional designs and ideas, particularly in human-powered craft. The links on this one appear to be dead, but the notion of using moving foils as propulsion on a "rowboat" is right up my alley. Look at the "foilsculler" on youtube to get something of the idea: . Another is Atsushi Doi's "Tandem Powerfin" - . A third related idea is this patent: Patent Images https://pdfpiw.uspto.gov/.piw?docid=05021015&SectionNum=1&IDKey=72CEE557C072&HomeUrl=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2%2526Sect2=HITOFF%2526u=%25252Fnetahtml%25252FPTO%25252Fsearch-adv.htm%2526r=34%2526f=G%2526l=50%2526d=PTXT%2526p=1%2526S1=440%25252F13.CCLS.%2526OS=CCL/440/13%2526RS=CCL/440/13.

In essence, the idea is to use two vertical blades (foils), fully immersed at all times, and pull (scull) them back and forth in opposition to each other. Sort of like a linear propeller. The thought being that deflecting water using these water-wings is more efficient than paddlewheels, or scoops, or traditional oars. Humans can deliver a great deal of torque but very low power, favoring lots of surface area moving slowly--very large diameter, low-speed props, or their linear equivalent--two foils, maybe 18" deep and 8" wide, shuttling back and forth along 5' tracks (length of stroke for big, powerful rower) on either side of a hull. My idea is to combine this with a spring return to retrieve the foils and provide more constant propulsion, and then use three hydroplaning pods, two forward, one back, like a hydroplaning speedboat, with a fuselage suspended in the center for the forward-facing "rower"/pilot, in place of a traditional displacement hull. A "sliding rigger" configuration allows the rower to pull the foils out by extending the legs, followed by trunk lean, then arm pull, thus giving the power advantage of sliding-seat rowing without the weight transfer that would be detrimental to maintaining a plane. Various proposals to change angle of attack of blades as boatspeed increases. The goal (obviously?) is the outright HPV water speed record, or failing that, a fun recreational craft that won't be too much of a pig at displacement speed and can really scoot if you are fit and feeling like a hard workout. As you say above, "what think ye?" I have pictures and something of a writeup.

3. Joined: Jul 2008
Posts: 510
Likes: 102, Points: 43, Legacy Rep: 32
Location: Ohio

### clmangesSenior Member

An illustration would help a lot, but if you're using the same type of foil as the foilsculler and powerfin, it would seem your five-foot tracks would be perpendicular to the boat's centerline. Do I have that correct? You did say 'back and forth', which implies motion parallel to the boat, and I can't see that working.

Anyway, the problems I see with these designs are that:
* the mechanisms take up a lot of space in the boat
* as near as I can tell, the fins look vulnerable to damage from submerged obstacles
* it will be tricky at best to bring the fins out of the water for launching or landing

I suspect also that any of these systems would have trouble coping with waves of more than about a handspan peak-to trough, especially beam-on or quartering.

If you want to operate something like this with a five-foot side-to-side excursion, the only way to go is with a catamaran.

Also, see this thread:
Did I invent this or is it old and/or failed? https://www.boatdesign.net/threads/did-i-invent-this-or-is-it-old-and-or-failed.65472/

4. Joined: Aug 2021
Posts: 16
Likes: 0, Points: 1
Location: Denver, CO, USA

### Horton HCCIJunior Member

CImanges-

I attached a short writeup of my idea to the similar thread "Twin flapping tail propulsion HPB." Attached here as well. It looks like there are several good threads on this topic, some newer than this one. :0|.

In answer to your questions, yes, five-foot tracks would be perpendicular to the boat's (fuselage's) centerline, forward of the center of buoyancy and the pilot. The motion of the foils would be opposed; both foils start alongside the fuselage, get pulled out to the outrigger sponsons along their perpendicular tracks by the rower, and then get pulled back in to the fuselage by springs/elastic.

You bring up good concerns, but I think many can be mitigated, at least to some degree. Fins could be removed by the expedient of unpinning the foil mast pintle from its gudgeon on the foil "sled," much as the rudder on a small sailing dinghy is removed, for instance. Sunfish and other such craft have a sprung "kick-up" feature if the rudder encounters an impediment. This might be incorporated.

Agreed that the configuration would likely not handle much in the way of waves, and would thus be confined to flat-water applications, as with a racing shell, in which class it would be intended to compete. I can't really think of a good way to get around this at present short of going to a hydrofoil, which I see as draggier than I'd like where flat-out speed is the goal.

I don't see how a five-foot excursion (ten feet, if both sides are considered) would need a catamaran configuration. Multihull, yes--but a trimaran rather than a cat. Here is a model that shows the basic idea: . The foil assembly moving in and out along the tracks (forward beams) would replace the air prop, in my design. A very beamy kind of trimaran, but in a sense no worse than a shell with oars extended. And no real "hull"--a bit like the Yellow Pages Endeavor or Sailrocket 2, in the notion of a fuselage riding atop, or suspended from, three planing pods. But no sail, of course. I'm working on a little RC model to try to test the foil action.

(This topic really doesn't make a lot of sense under the "Schmidt Wave Propellor" heading, so I suggest moving to the "Twin flapping tail propulsion HPB" thread if there is further interest. Jakeeeef's original question/idea is pretty close to what I'm envisioning.)

#### Attached Files:

• ###### DaggerRo Description (abridged) v1.pdf
File size:
390.2 KB
Views:
39

5. Joined: Jul 2008
Posts: 510
Likes: 102, Points: 43, Legacy Rep: 32
Location: Ohio

### clmangesSenior Member

I'll follow this over on the other thread.

I'm not sure how much success you'll have trying to support a person on three little pods. Study how planing hulls work. A high-school friend of mine built a dirt-cheap little hydroplaning boat meant to run with an outboard of maybe 5HP. It looked like a flying saucer with the back half cut off plumb.

Some of the strangest things will get up on a plane, though. The Oz Goose routinely does, and blasts along at 15 knots and up, and it looks like a john-boat.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.