Fin sandals to jet fins

[Sam Miller III]

Subject: Fins

Some time ago there was a thread on fins. A gentleman from Italy came on stong and the best I could comprehend his post he gave Italy and their designers/ engineers credit for the swim swim--Nonsence!


Many years ago I became interested in recreational diving fins, so for approximately 15 to 20 years I researched the history of fins and developed a very large file on the subject, This research resulted in a much abridged six page article.


Therefore, I would invite all of you to read the US Historical Diving Society journal, 1994, "History of fins." HDS #3,#4 & #5.


A very short history of fin development in the US and the world is as follows;


1868 Havlor Olsen "Fin Sandals for the feet." (US)

1932 Commander Luis de Corlieu "Swimming propellers" (aka Fins) (France)
1933 European patent
1937 US patent
*** Based on "the discontinuity of impulsion destroys the yielding power efficiency of a propulsion device"--what ever that means???




1938 Owen Churchill discovers Swimming propellers in Tahiti
1939 Churchhill & de Corlieu enter in to a contract to produce Swimming propellers
1940 Owen Churchill produces design patent and a improvement patent (US)
1940 Churchill produces 946 pairs of "Swim Fins"

1945 Pop Romano's Sea Net company produces "FROG FEET" (US)

1947 C.H. Wilen produces "Swimming tales" (Italy)


1952 Art Brown produces "Duck Feet" Spearfisherman Company (US)



1965 George Beauchat US patent for Jet fins (France)

(then Rockets -US Divers; 707 - Sportsways etc)

Can Luis, Captain, Nemmie, Mike or any one explain the

"the discontinuity of impulsion destroys the yielding power efficiency of a propulsion device"

In plain talk? In engineerese? In dive talk?

 

[JamesBon92007]

I am "none of the above" but the "discontinuity of impulsion" statement sounds a lot like what Scubapro was saying about fins when they first began marketing Jet Fins in the USA. Perhaps this refers to the "dead spot" that supposedly exists in swim fins.

Was the Beauchat US patent for Jet Fins the same patent that Scubapro used or was it a different patent? The fins were very similar but the only ones I've ever seen sold in the USA had the Scubapro logo on the top of the fin, and not just "Jet Fin."

 

[Eric Sedletzky]

Subject: Fins

"the discontinuity of impulsion destroys the yielding power efficiency of a propulsion device"

In plain talk? In engineerese? In dive talk?

The way I read it in regards to using fins is that if you are finning along, stop, then resume finning again you waste energy by having to get back up to speed. So in other words, even though you stopped and rested for a second, to get moving again requires more energy than if you were to never have stopped at all.

Or like James Bond said, some fins suck and have "flat" spots in their power cycle making them less efficient.

 

[Sam Miller III]

It was referred to as the "Law of Cubes--the discontinuity of impulsion destroys the yielding power efficiency of a propulsion device" so far no one has idenified the law of cubes as a valid law..

The Jet fins holes were based on a venturi effect and IDed as "swimmer's foot fins thrust accelerating device." Recall no other fins were made with over lapping holes???
sdm

 

[JamesBon92007]

Sam, I'm not sure if that's a question or not but yes, I have some Nemrod Venturis that overlap all the way to the end. If we can take that a step further and add some turbines with flywheels inside the venturis then perhaps the "discontinuity of impulsion" would be a moot point

Here's a quote from an article about Beauchat from Wikipedia:

"Vented fins
Vented fins were first designed in 1964 by Georges Beuchat and commercialised as Jetfins. The Jetfin tradename and design were sold to Scubapro in the 1970’s. This style of fin is strongly favored by technical divers that use a frog kick allowing a high degree of control but sacrifice speed for low oxygen consumption.[citation needed] Vented fins are generally stiff paddle fins that have vents at the base of the foot pocket. The vents are intended to allow for the passage of water during the recovery stroke, but prevent passage during power strokes due to the blade angle, attempting to lessen effort during recovery and improve kick efficiency. A review and study by Pendergast et al in 2003 concluded that vented fins did not improve economy, implying that water does not pass through the vents."

What I get out of this is that Jet Fins don't work. However, my feet tell me they work better than anything else they've ever had on them.

 

[Sam Miller III]

The point of the post was to ID the first time fins were referred to as Fins, Frog feet, Duck feet etc

FYI
Ferraro/Cressi fins, 1962 were vented with a flap cover
SCUBA Pro 1963, were vented with a flap cover
Healthways 1965,were vented with a flap cover


Marzella fins, 1962 twin blade surfaces-- ie post hole diggers

1965 Jet Fins =SCUBA Pro "Jet Fin" in script on top of blade--Imported

They seem to work for me..but not as well as Ducks

 

[Luis H]

There has been a lot of talk about the vents on Jet fins not working or working. Some divers (Nemrod for one) have actually ducked taped the vents shot to see if it made a difference.

To me the ducts are not so much a hydrodynamic feature as much as a structural box section which provides the proper mid-section stiffness. The bottom line is that the Jet fins work and have worked extremely well for me for the past 40 years. I have tried other fins, but always go back to Jets (or direct copies of the Jet, the OMS).

I know the vents were advertised as a hydrodynamic feature, but I think that the geometry function as a structural feature that gives the proper flex to the fins. This might have been an unintentional side benefit, but IMHO it turn out to be the primary advantage of the Jets. This is just my opinion.



Sam

I am not sure what they are trying to say, but when I see a lot of technical terms thrown together in a short sentence, to me it sounds like a lot of techno babble thrown together by marketing to try to impress someone… “If you can’t baffle them with brilliance, befuddle them with bull sh..”.

I may be totally wrong about that statement. There may be some intelligent thought behind it, but in the Scuba industry I just see so many terms thrown around just to impress the customers or just other divers.

I always believe that language should be used to explain to the audience not to confuse them.

 

[JamesBon92007]

The point of the post was to ID the first time fins were referred to as Fins, Frog feet, Duck feet etc

FYI
Ferraro/Cressi fins, 1962 were vented with a flap cover
SCUBA Pro 1963, were vented with a flap cover
Healthways 1965,were vented with a flap cover


Marzella fins, 1962 twin blade surfaces-- ie post hole diggers

1965 Jet Fins =SCUBA Pro "Jet Fin" in script on top of blade--Imported

They seem to work for me..but not as well as Ducks

The point of the post is interesting and all but you can't expect us all to not comment on something as esoteric as "discontinuity of impulsion."

Which Ducks do you like the best? I was inclined toward the amber ones rather than the black ones because of the difference in flexibility but then they no longer seemed to be available. I think Voit started making some with adjustable straps right around then but they somehow didn't look right.

 

[Walter]

Thanks Sam, this is a fun thread.

 

[John C. Ratliff]

Sam, I'm not sure if that's a question or not but yes, I have some Nemrod Venturis that overlap all the way to the end. If we can take that a step further and add some turbines with flywheels inside the venturis then perhaps the "discontinuity of impulsion" would be a moot point

Here's a quote from an article about Beauchat from Wikipedia:

"Vented fins
Vented fins were first designed in 1964 by Georges Beuchat and commercialised as Jetfins. The Jetfin tradename and design were sold to Scubapro in the 1970’s. This style of fin is strongly favored by technical divers that use a frog kick allowing a high degree of control but sacrifice speed for low oxygen consumption.[citation needed] Vented fins are generally stiff paddle fins that have vents at the base of the foot pocket. The vents are intended to allow for the passage of water during the recovery stroke, but prevent passage during power strokes due to the blade angle, attempting to lessen effort during recovery and improve kick efficiency. A review and study by Pendergast et al in 2003 concluded that vented fins did not improve economy, implying that water does not pass through the vents."

What I get out of this is that Jet Fins don't work. However, my feet tell me they work better than anything else they've ever had on them.

Actually, this quote is not correct. The vents for the Jet Fins were designed to augment the down stroke, not the recovery stroke. This is described in the patent (as I recall--my copy has been temporarily misplaced). The idea is that just beyond the toe of the previous fins (such as the duck foot fin), this area was a "dead" area where water did not move. By providing the vent, and having another blade parallel to the top blade, the theory was that it would provide another surface to push off of. The vented water would "jet" to the rear rather than just through the fin, according to the theory.

I have done a lot of fin research, and have found that for the most part this seem correct. However, it also does nothing for this "dead" area on the up (recovery) stroke. This is well-described in the ScubaPro catalog for 1986.

There were some fins which reversed the position, of a vent which worked on the up-stroke, but it was not the Jet Fin. I believe it may have been a Waterlung (Sportsways) fin.

Dr. Miller, didn't Ben Franklin have something to do with the development of the first fins?


SeaRat