Lunocet photos from DEMA

Zerog,

What, when, and how much are you planning for the clinics at Ginnie? That is in range of me. If things are not settled yet, please put me on the PM list.

Connor

We are getting a group together for late January, please join us... there will be no charge. We are looking to provide demos and to share some breaching technique. I am planning on making demo/ breachng clinics a regular activity; maybe once a month.

I'd really like to stage breaching competitions starting this summer at Ginnie... with the water so clear, photography of a perfect breach would be ideal there.

Please email me if you would like me to send more info on the events...
zerog@windstream.net

Thanks,

Ted

Ted in the first week of February Davide Carrera will be coming to the Bahamas to hold a course and stay on until Vertical Blue in April. He is the only person I have heard of who has performed a successful complete body exit with a monofin - it is a combination of his short stature, power and incredible flexibility (to arch the back and whip the feet out before the hands reenter).
I can ask him about his technique and pass this on to you guys if you want, or you could even come and dive the blue hole with us to swap ideas.
Cheers, Will.

Yes, please pass it on... I would really like to get him on a lunocet and would like to speak to him about his technique... thanks.

Hi!

From Breacher to Breacher...

I´ve been trying out a series of experiments about
dolphin-style propulsion with stiff, hydrofoil-like
blades...

http://forums.deeperblue.com/746374-post43.html

...and arrived at the following conclusion:

The angle of attack of a hydrofoil can (easily enough)
be controlled by the means of springs or other elastic
elements, but...

This is not the way marine mammals accomplish it!

As we lack the kind of anatomy and muscles they
use to do so, another trick seems to fit us poor
human beings better:

I´ve been trying the use of angular hard stops to
control the angle of attack (completely avoiding the
use of any elastic element).
Apparently a bowden-system (much like bicycle-brakes)
with a handheld control is the best solution to dynamically
adjust the exact position of the angular hard-stops.
The effect compares to the gear-shifting in bikes.

By doing so, the angle of attack does not depend on the
force one applies to the fin, meaning that you can have
a flat, hi speed-angle, EVEN if you apply ALL your strength.

The use of elastic elements would mean that the angle of
attack gets steeper (low speed angle) when you apply more
force. Thus a speed limit is being obtained.

As soon as I get back home again, I´ll try to add some pics.

...just an idea...

I would love to see a direct comparison between two divers of about equal ability. One with a Hyperfin or other conventional Monofin and one with a Lunocet. (i.e. a race or breaching competition) To me, this would be the best way to tell definatively whether or not the Lunocet is faster than a conventional monofin. Also, i'd love to know how the Lunocet compares to the Finis competitor monofins, they are probably heavier, but the blade on the Finis monofins looks to have more surface area. Do you think this matters much for generating power/speed?

The Review will be up within a few days and I'll be happy to answer any questions it doesn't answer.

On Drag for Lunocet or Monofin,

I believe Eric Fattah' comment that the Lunocet needs to have less drag to be effective as good monofin and Zerog's experience indicating the that the Lunocet is proven much faster and more powerful than standard bi fins are correct even though they may seem contradictory and I offer a simplified explanation on the affects drag below to illustrate this.

Max speed corresponds to = ratio of max thrust divided by drag, this is true and is not simplification for any object unaffected by gravity (neutrally bouyant in water)

Lets assume the following for each (NOTE is made up data for example):
Standard Bi-fins = 1 unit thrust and 1 unit drag
Lunocet= 3 unit thrust and 2 units drag
Advanced Mono= 2 units thrust and 1/2 unit drag
Competition freediver = 2 units drag
Scuba Diver = 8 units drag

Test 1: Scuba diver with standard bi-fins vs advanced mono vs Lunocet :

Scuba Diver with bi fins = (8+1) = 9 units drag and 1 unit thrust.
Ratio of thrust to drag = 1/9 = 0.11 = very slow

Scuba Diver with advanced mono = (8+1/2) = 8.5 units drag and 2 unit thrust.
Ratio of thrust to drag = 2/8.5 = 0.25 = over twice as fast as Bi-fins.

Scuba Diver wtih Lunocet = (8+2) = 10 units drag and 3 units thrust.
Ratio of thrust to drag = 3/10 = 0.30 = Way faster than Bi-fins and faster than advanced monofin for scuba diver

Test 2: Competition freediver with Bi fins vs Lunocet vs advanced mono:

Competition freediver with bifins = (2+1) = 3 units drag and 1 unit thrust
Ratio of thrust to drag = 1/3 = 0.33 = faster than scuba with Lunocet

Competition freediver with Lunocet = (2+3) = 5 units drag and 3 units thrust
Ratio of thrust to drag = 3/5 = 0.6 = very fast, fastest yet.

Competition freediver with Advanced Mono = (2 + 1/2) = 2.5 units drag and 2 units thrust
Ratio of thrust to drag = 2/2.5 = 0.8 = Fastest of all.

So how come Lunocet is much faster for the scuba diver and quite a bit slower for the competition freediver?

This is because the Lunocet has 4 times the drag of an advanced mono (in this example may or may not be true) and this "wrecks" the competetition freediver/Lunocet drag combo which makes total drag double from 2.5 units drag to 5 units drag and even though the Lunocet in the above example is given 50% more thrust, 3 compared to 2 for the advanced mono, this extra thrust doesn't make up for the extra drag.

In the case of the scuba diver, the scuba diver drag starts at 8 units drag so it doesn't matter much if the Lunocet has drag count of 2 units or 1 unit like the bi fins or 1/2 unit like the advanced mono as it doesn't change the total drag much at all while the thrust changes alot with the Lunocet over the bi-fins and advanced mono.


So conclusion from above is that even though Lunocet has in example 50% more thrust than advanced monofin (3 units compared to 2 units thrust) it is slower than advanced monofin on competition freediver due to the large extra chunk of drag the Lunocet adds RELATIVE to the competition freediver. This is because a competition freediver has very low drag due to neck weight instead of weight belt, streamline mask/goggles, streamline suit and streamline head, neck, and over head hand and arm position. So when zerog tests the Lunocet vs the advanced mono in his pool the test may not be same as advanced freediver as zerog arm and head position are not optimal for streamlining like competition freediver (note this is very hard to achieve, takes lots of stretching etc so is not meant to criticize zerog for this, I and most freedivers have same issue).

Cheers Wes Lapp

Interesting Wes. Just one comment that doesn't affect the arguement much.

"Scuba Diver with advanced mono = (8+1/2) = 8.5 units drag and 2 unit thrust.
Ratio of thrust to drag = 2/8.5 = 0.25 = over twice as fast as Bi-fins."

When you talk of speed, you use the square rule. 'over 1.5 times as fast as Bi-fins' in this case.

considerations of speed are sort of moot if you don't take endurance into account. The revision of the lunocet we tested, for example, can handle a great deal of force - so it will out accelerate a good set of freediving fins from a dead stop. But if you start to talk about maintaining speed over any sort of meaningful distance things change.

Chris,

I read your write-up on the lunocet and am now wondering how your leg is?

What did you do to it? Is it healed?

I'm good Jon. It was sore for a couple of weeks - but never debilitating and didn't cramp my style diving-wise.

Bill,

Thanks and that is correct, it should read 'twice the thrust over drag ratio".

This would not make it twice as fast, if the thrust was constant with higher velocity which could be possible then speed increase would be 1.41 as drag increases with the square of velocity for a doubling of thrust/drag ratio.

Correct too Fondueset that this does not factor in efficiency which would affect available endurance. In the case of doing a single breach then I would think endurance would not play much of a part as would be only 2-4 second sprint.

The idea of testing a Lunocet against a monofin for breaching is very compelling to me as it would seem to be very easy to compare simply measuring how high one got with each and this should correspond quite well to max sprint velocity which is a function of the thrust/drag ratio.

It would be pretty straight forward to calculate the exit velocity of a swimmer based on their center of gravity max height achieved and from the exit velocity the ratio of thrust/drag that they had.

Cheers Wes

Front Page Lunocet was very interesting indeed, so definitely an upgrade model is in the making and you guys gets to test it again:friday

I read the report on the Lunocet. Very interesting. It sounds very possible that the hydrodynamics of the fin are producing a turbulance that creates alot of drag. Perhaps similar to the problems faced by jet aircraft designers when using a straight wing rather than swept wings. I know one problem they would have (even with swept wing designs) after the initial accelaration of the aircraft was that alot of drag was being created by airflow escaping laterally off the side of the wing (the Russian Mig-15 actually used veritcal stabilising 'gates' to force the airflow back over the wing and keep it from moving laterally along the wing's surface.) Keep in mind that any air/waterflow that is not producing lift/thrust is producing drag. I would be curious to see what certain alterations might acheive in a new iteration of the design. For example, trying more of a delta wing design that is more swept back then the current wing angle? I was just observing that conventional monofins are more of a true delta wing design than the lunocet. Please let me know what you think. Again, great write-up, I enjoyed reading it alot.

Thanks Bob,

Ted's opinion, in our last conversation, was that there is a strong possibility the shoe configuration was, in addition to creating drag, disrupting the way thrust is generated by the Lunate design - which, incidentally, does involve vectoring the thrust inward. Remedies may involve shiftin the foil axis toward the toes, streamlining the footpockets and other components, etc.
I can tell you that the foils themselves are very low drag - they pretty much slice right through the water.

In our last conversation Ted seemed much more interested in extending the range of functionality of the Lunocet beyond the focus of just breaching.

I think, also, that the discovery of ankle braces has lessened the need to compromise around ankle stress. I think the ankle stress probably comes from the fact that the lunocet's rigid foil transmits force more abruptly than a conventionl monofin - resulting in what amounts to repeated impacts when extreme force is applied. A conventional monofin softens the force curve by storing more of the energy and releasing it gradually.

Hi there!

A very simple and intuitive way to try
out the trust developed with different
kinds of fins is the rope-pulling-game.

So, take a piece of rope with a handlebar
on each end and let the two of them
do their best!

...better than number-crunching...

Would be good if you could find a pair of twins...

Good report, thanks Fondueset. I'm a bit surprised by the "high drag is ok for breachers" reasoning. I would have thought that drag would be an even more important consideration for breachers than it is for freedivers. After all, breaching is all about your peak speed, and peak speed is largely determined by the drag you incur rather than the amount of thrust you can generate. With perfect (dolphinesque) streamlining you could breach with no weightbelt and a pair of duck fins. In fact if you had a way of getting down to start with (rope?) you could do away with the duck fins and rely only on your terminal ascent velocity...

The logic there is that a breach is generated in about three or four kicks right near the surface and is primarly the result of a high energy burst - with a need for it to be transmitted directly to the water with as much fidelity as possible and followed, in all probability, by a pretty intense gymnastic maneuver.

Fondueset said:

The logic there is that a breach is generated in about three or four kicks right near the surface and is primarly the result of a high energy burst - with a need for it to be transmitted directly to the water with as much fidelity as possible

Click to expand...

In order to provide..... speed??

Not your logic I know, so I don't want to shoot the messenger. But it makes no sense to me. It's like a long-jumper saying "I don't need a runup with a high peak speed because the jump is only 'generated' in the last couple of steps. I think I'll wear gumboots."