Basic gear from mid-twentieth-century Italy: Other manufacturers

[lowwall]

But several years later, Cressi released a Rondine fin equipped with a moving vane. This did open during the down kick, leaving the water flowing through, and did close during the upward kick, providing a much larger active surface.
The explanation provided was that the downward kick was ineffective, whilst the upward one was more effective.

That makes no sense (except as a marketing exercise perhaps). Humans generally have more power on the forward stroke than backward. My quick search suggests that the hamstrings are typically around 70% as strong as the quadriceps. You can equalize this via weight training or focused exercises. Perhaps this occurs - either naturally or purposefully - during fin swimming training, but it wouldn't apply to the average person.

Personally I think that employing modern carbon-fiber fins, of proper length, proper stiffness and proper angle, employed by a well trained swimmed-finning or underwater-speed athlet, there is no "negative" movement.
The fin is driven into a sinusoidal motion, with a rate matching the natural frequency of the blade, which is maintained "in resonance".
In these optimal conditions a large part of the work done by the muscles translates efficiently in forward thrust.

I don't have sufficient knowledge in this area to comment on your thoughts. But regarding the sinusoidal motion, have you seen the footage of the experimental Force Fins with the long tail and ball at its tip? There's a short video somewhere, but this is the best I could find (at 4:42). @Bob Evans?

My opinion is all those early fin designs, including the Jetfins, were attempts to counter-effect inefficient kicking styles employed by beginners or untrained finned swimmers.

I think paddle fins, including Jetfins, were optimized for quick turns and body position changes rather than top or sustained speed. Remember they were introduced when the market was interested in spearfishing. Agility and getting the most out of the first couple of kicks were more important than sustained speed, you aren't going to catch most game fish by chasing them down. I think they've stuck around because wreck and cave divers also value precision over sustained speed.

 

[Bob Evans]

That makes no sense (except as a marketing exercise perhaps). Humans generally have more power on the forward stroke than backward. My quick search suggests that the hamstrings are typically around 70% as strong as the quadriceps. You can equalize this via weight training or focused exercises. Perhaps this occurs - either naturally or purposefully - during fin swimming training, but it wouldn't apply to the average person.


I don't have sufficient knowledge in this area to comment on your thoughts. But regarding the sinusoidal motion, have you seen the footage of the experimental Force Fins with the long tail and ball at its tip? There's a short video somewhere, but this is the best I could find (at 4:42). @Bob Evans?




I think paddle fins, including Jetfins, were optimized for quick turns and body position changes rather than top or sustained speed. Remember they were introduced when the market was interested in spearfishing. Agility and getting the most out of the first couple of kicks were more important than sustained speed, you aren't going to catch most game fish by chasing them down. I think they've stuck around because wreck and cave divers also value precision over sustained speed.

 

[lowwall]

Sperm Force!

 

[Angelo Farina]

The claim made by L.Ferraro when he invented the Super Rondine was that the forward kick was less efficient (not less effective - excuse my bad English). The forward-acting muscles are actually stronger, but most of the available force is lost moving the water down by the part of the fin close to the foot. Hence creating an opening vane there avoids to waste that force in not-propulsive water displacement.
The Force Fins videos are very interesting, but are nothing compared with the secrete Russian video which I managed to see during my training for becoming a finned swimming instructor and trainer, in the eighties.
One of my teachers was a former Russian athlete, who had a VHS tape showing the tests performed in a Russian university in a water tunnel with the aim of defining the optimal kicking for maximum efficiency.
At the time (around 1985) Russian athlets were dominating in finned swimming and underwater speed competitions. They were the first to build fiberglass fins with positive angle (later evolved in carbon-fiber monofins).
Russian scientists did find the theoretical equations defining the resonance frequency and wavelength of resonating fin blades, starting from the equations of resonances of structure-fluid interactions of elastic bodies (namely the reed of some wind musical instruments).
They extended the theory for optimising the thrust-to-force ratio. In those years there was a black market of those Russians hand-made fins here in Europe...
We were trying to copy them, but we never managed to get those equations, so our copies of their fins were optimised the old way, by trial and error.
My teacher was an ex athlete, he told us on how scientists were designing an individualised fin for each of them. He did explain us qualitatively how they were working, but he did not know the quantitative formulas making it possible to calibrate the fins for the geometry and strength of the legs of a given athlete.

 

[Compressor]

@David Wilson Thank you for the excellent documentation you have presented. Very well done.

 

[David Wilson]

@David Wilson Thank you for the excellent documentation you have presented. Very well done.

Thank you for your acknowledgement, Compressor, and to everyone else who posted messages and thanks. The Tigullio Giada has generated so much comment and discussion that I feel I cannot move on yet to GSD. I do not intend to pass comment on the hydrodynamics of fins and finning as the grounding in physics I received at my selective boys' secondary school here in the UK was so inadequate that I committed myself more and more to the study of the arts and humanities, especially languages, whose rules, structures and workings proved far more attractive and intelligible to my adolescent mind. I have never regretted making that choice when at school but I have regretted my university setting me literary texts to translate but never ones relating to science or technology. Any attempts at those writings have been self-taught on my part since the the 1970s.

What I shall do to contribute to the Giada debate is to add another publication into the mix. A German fin patent granted to the Tigullio company in the mid-1960s and hence unlikely to relate to Tigullio's earlier flagship fin, the Manta. I believe I mentioned that the Italian term "brevettata" (patented) was applied to the Giada design and German Patent number DE 1928422U appears to fit the bill. I managed to find a copy in the European Patent archive at DE1928422U: Espacenet - Original document and date-stamped 4 October 1965.

Here are the German patent drawings:

 

[David Wilson]

Where, you might ask, is the text of the patent, where all should be revealed about the claims and principles of the Tigullio invention. To tantalise you, I will post the first page of original German text followed by my own translation. I have a Master's degree in the language, albeit based on literary studies, but my rendering will pay a good enough tribute to the language of the text if not to its scientific subject-matter.

German text:
Die Neuerung betrifft eine einstückig aus elastischen Material, z.B. Gummi oder Kunststoff hergestellte Schwimmflosse, bestehend aus einen zur Aufnahme des Fußes dienenden, z.B., schuhförmig ausgebildeten Fußteil und einem blattartigen, sich vom Fußteil nach vorn erstreckenden und in Bezug auf die Fußsohlenebene vorzugsweise etwas nach unten geneigten Flossenteil, der durch längsgerichtete Rippen verstärkt bzw. versteift ist.

Es ist bekannt, daß derartige Schwimmflossen beim Craulschwimmen eine etwa waagerechte bzw. etwas nach hinten geneigte Lage einnehmen, wobei die Sohle des Fußteils und die untere Fläche des Flossenteils schräg nach hinten, die obere Fläche des Flossenteils dagegen schräg nach vorn in Bezug auf die Schwimmrichtung gerichtet sind. Infolge der Beinbewegung des Schwimmers wird die Flosse nach oben und nach unten geschlagen, wobei der nach oben gerichtete, den Hauptanteil der Vortriebskraft liefernde Bein bzw. Flossenschlag in Folgenden kurz "Aufwärtsschlag" und der nach unten gerichtete, die Flosse in Ausgangsstellung für den nächstfolgenden Aufwärtsschlag zurückführende Bein- bzw. Flossen-
English translation:
The innovation relates to a one-piece swim fin made of elastic material, e.g. rubber or plastic, consisting of a foot part serving to hold the foot, e.g. shoe-shaped, and a blade-like foot part that extends forward from the foot part and preferably slightly downwards relative to the sole of the foot inclined fin part, which is reinforced or stiffened by longitudinal ribs.

It is known that swimming fins of this type take an approximately horizontal or slightly sloping backward position when swimming the crawl stroke, with the sole of the foot part and the lower surface of the fin part being directed obliquely backwards and the upper surface of the fin part obliquely forwards relative to the direction of swimming. As a result of the swimmer's leg movement, the fin is flicked up and down, with the upward-facing leg or fin stroke providing the main part of the propulsive power in the following briefly "upward stroke" and the downward-facing, the fin in the starting position for the next upward stroke returning leg or fin...

So where now is the second page of German patent text? Here is the scanned copy provided by the European Patent Office:

Notice any difference? Yes, a considerable deterioration in the quality, and hence legibility, of the text after the first page. So much so that the excellent optical character reader (New OCR) I habitually use to save myself having to retype text manually inevitably gets every second letter wrong and I end up proofreading gobbledegook. The remaining eleven pages of patent text are equally or even more illegible than the second page.

I am hoping (a) that the legible first page and the three patent drawings will suffice to provide my readers with an inkling of what the patent is about and that (b) they will return to report whether the text and illustrations leave us any the wiser. Anyone with sufficient knowledge of German and understanding of technical subject-matter expressed via the jargon of "patentese" is welcome to download the Tigullio fin patent themselves from Espacenet at Espacenet - Original document and wrestle with the existing blurred typing to elicit its meaning. I think I have already done all I can with this official source of information without either ruining my eyesight or testing my patience to the absolute limits.

I am now going to wait until the weekend before carrying out my original intention to move on to the GSD underwater products company. Please feel free to post in the meantime. Keep safe and stay well.

 

[Angelo Farina]

Thanks @David Wilson , you made an excellent job. This patent clarifies everything and confirms that, at the time, the upward (backward) stroke was considered the more useful stroke, while the downward (forward) kick was considered less effective. Hence the fin was profiled for optimal backward kick. Furthermore, the fin blade had negative slope, as the original Rondine (whilst Russian hand-made glass-fiber and carbon-fiber and Force Fins have positive slope of the blade).
I think that this is enough for the Giada...
And I am very anxious to read about the GSD, which manufactured my first pair of fins, mask and snorkel, replaced by the original Beuchat Jetfins just after my first certification.

 

[lowwall]

It appears that the sides of the fin were designed to collapse on the downstroke to lessen surface area and thus power. This is the opposite of Force Fins where the tails crease on the upstroke and then snaps back at the start of the downstroke.

The relative success of Force Fins - which are still available despite prices that have gone from merely premium to breathtaking - versus the Giadas argues for the superiority of that approach.

I have a pair of Force Fins Pros and, in my own timed tests, have found they work as well as my Scubapro Go Sports while being more compact and comfortable. It would be fun to compare them directly against the Giada.

 

[Angelo Farina]

It appears that the sides of the fin were designed to collapse on the downstroke to lessen surface area and thus power. This is the opposite of Force Fins where the tails crease on the upstroke and then snaps back at the start of the downstroke.

The relative success of Force Fins - which are still available despite prices that have gone from merely premium to breathtaking - versus the Giadas argues for the superiority of that approach.

I have a pair of Force Fins Pros and, in my own timed tests, have found they work as well as my Scubapro Go Sports while being more compact and comfortable. It would be fun to compare them directly against the Giada.

I add a last info confirming what you wrote. The Russians athletes developed their racing fins starting from a local copy of the Rondine fins, in blue rubber. For reversing the "good" side with the "bad" side, the Russians did use the fins upside-down, cutting a hole in sole, so that the foot was inserted through it.
This resulted both in a positive slope of the blade, instead of the original negative slope, and having the side ribs protruding on the top of the fin, instead of below.
Both things provide benefits for fast, efficient kicking, provided that the athlete learns how to use them properly, and trains with them. For a novice, instead, the traditional downward slope and ribs on the lower surface work better, because the novice does not know how to kick properly.
A big part of my work as a finned swimming instructor was to de-instruct my students for forgetting their wrong habits, so they could make good use of their legs.
Unfortunately nowadays most diving instructors, particularly "tech" instructors, do not teach to kick properly. They are more interested in keeping the reef safe from kicks, and to avoiding silting inside a cave or a wreck, than providing efficient propulsion and high speed.
Furthermore they do not teach anymore how to use hands with the opposition movement, a practice which disappeared already in the eighties (as it did require months for being mastered).
Finned swimming competitions are not anymore so common, and most people who start diving does not come anymore, as it was in the past, from years of spearfishing in free diving.
Year after year I have seen that the number of divers who have bad kicking increases, instead of diminishing.
Studying the fin development in the sixties and seventies is very interesting, as this history was made of ideas (often wrong), experiments and failures.
One could expect that fin designers did learn from those wrong concepts, errors and failures. Instead you can see everyday those old concepts resurfacing, and detrimental design (such as the modifications done by Scubapro when they got the license for the Jetfin from Beauchat) continuosly replicated.