Lunocet photos from DEMA

[efattah]

There is only one way I can envisage a breach with high drag, and that is using the 'jump box' method. I tried building a 'jump box' in Vancouver but it was a total failure. Basically a jump box is a device on which you literally jump off of, kind of like pushing off the wall in dynamic. The caveat is that whatever you 'jump off of', you must bring with you. I tried building a set of bolding 4ft wide blades that would collapse after you jumped off them, but the collapse drag was huge.

I tried 'jumping' off of the lunocet right at the surface, essentially a single stroke breach, but I was not able to get enough momentum from the single back stroke to get much out of the water.

 

[Bill]

Interesting problem when I look at it this way-

Peak speed is not as important as 'speed' (vertical velocity) at the point where you lose thrust.

When the head and shoulders clear the water, drag is dramatically reduced but somewhere in here gravity takes over.

An high jump flop over the bar backwards appears to require almost half a meter above the bar by the nose, navel and knees but not at the same time.

This seems to indicate that about three meters per second when the hips clear the water and one last kick that starts the rotation too, should do it.

Is three m/s humanly possible?

To balance gravity at that point you'd also need about a 60 mm wet suit bottom.

 

[Fondueset]

Will T knows a guy who can breach with a mono. He is very compact physically, and very strong and flexible. I don't have an exact description but it sounds like the guy really wrenches himself around in the air to completely clear the water.

 

[jome]

Interesting problem when I look at it this way-
Is three m/s humanly possible?

Finswimmers go faster than 3 m/s. The world record in 50m apnea sprint is around 14 seconds (last I checked) which would give about 3.5 m/s (which is also why I think the claim somewhere that you could maintain 10mph cruising speed with the lunocet sounded a bit sensational - but I don't know where that came from). 3 m/s would mean 16.5 sec sprint which is fast, but not impossible even for a non-professional swimmer (but you'd need to be semi-pro )

I'm working on the twins problem, if someone could just supply me with a really small lunocet and monofin we could solve this forever .

 

[laminar]

I think there's no way you could go faster than a monofin given the Lunocet's current construction.

Strokes per distance is misleading. As Chris said in the article I did 5-6 strokes with both the Lunocet and Hyperfin to ascend from 15m. But the difference was the effort needed to overcome the drag of the Lunocet and the drag created by the wide amplitude stroke. To breach you need higher efficiency and more power. Perhaps the Lunocet has the potential to access power in the quads, however, the application of that power will lack the efficiency (drag reduction) required to leap out of the water.

I still believe that the key to breaching is to be able to generate power without a wide undulation. That is what finswimmers excel at - going fast with minimal drag.

Also, I saw a regular swimmer do a vertical dolphin kick without fins up to his knees (to hit a flutter board held overhead by his coach) at a pool in Florida. So with excellent strength, flexibility and explosive coordination, I think breaching with a monofin is possible. The way the lunocet works now (current version), that wouldn't work.

The jumping off the water approach to breaching may result in a breach, but I think it may feel like a standing jump?

Hopefully, Ted will find the right formula for a easy breach. That would be a lot of fun.

Pete

 

[trux]

I still believe that the key to breaching is to be able to generate power without a wide undulation.

Yes, that makes sense. That's also why in this thread I suggested a variable stiffness for Lunocet - a gear where you could adjust the stiffness (and hence could reduce the kick amplitude) as you speed up. Or that it adjusts itself automatically. You simply need a different stiffness and different kick amplitude when accelerating from zero, than when already at cruising speed and trying to achieve the peek velocity. If I understand the current concept correctly you either adjust the stiffness to allow you easier acceleration from stand point, or make it stiff for high speed. In the first case you won't be able to get any high speed because the foil will bend too much and cause a lot of drag. In the second case you won't be able to accelerate efficiently and lose all your energy before being able to achieve the peek velocity. It is like trying to win Tour de France with a bicycle without any gear.

Ted liked the idea of a variable stiffness, but that was in the time he had the variant with the bungee. Since then, he simplified the concept, which had many advantages, but adding the on-the-fly adjusting of the foil tension may be technically challenging. Would be great though anyway.

 

[laminar]

Ted, check out windsurfing sails for inspiration.

They adjust on the fly from high power at lower speeds/wind power (deep camber) and decreasing drag profile at higher wind power (twisting camber, floppy leech/trailing edges).

Should hold true for water, as well.

 

[terrafugia]

When it comes to breaching, I think speed is more important than power. When you consider the “fun factor”, I think this is an even more true statement.

Think about darting out of the water at high speed for a breach, and then diving back in and slicing through the water without bleeding off the speed such that you can add a few kicks and do it again. Then, compare that to a forceful power leap where you are using the fin as a temporary hydrofoil to support your weight while you jump out of the water.

To me, the first description sounds graceful and exciting. The second description sound a lot like jumping into an elevated swimming pool from the ground level. I think the key to successful breaching is aggressive streamlining as opposed to more powerful propulsion. The problem is that when you get streamlined, you will end up looking like a dolphin instead of a finswimmer.

 

[wes]

Nice points and posts, all.

I think the point that Fondueset was making that drag wasn't everything in breaching is very interesting as for sure as you exit the water you will lose the drag from your upper body in the water. Of course the fin is still in the water so maybe fin drag is much more important then head and shoulder (and mask) drag.

Also as to which is more important, thrust or drag there is an answer to that and it is the ratio of thrust divided by drag. If you have a fin with 2x the thrust and 2x the drag you haven't gained anything. On the other hand that swimmer that could dolphin kick up to his knees maybe had 1/2 the thrust of a monofin and only 1/3 the drag due to very streamline swim technique so would do better in thrust divided by drag. This is why the breach test is so keen, even if a fin can produce monster thrust it must still have minimal drag or nothing is really gained.

Cheers Wes

 

[terrafugia]

I totally agree with you WES, it is a function of thrust to drag ratio. They are both important. In fact, that ratio is what will determine your maximum speed. I guess the point that I did not make very clear is that I’m thinking a monofin already has pretty good thrust. I have no doubts that it is possible to increase that thrust through more efficient hydrodynamic propulsion, but without lowering the drag, I’m not sure you can make enough difference to get the effect we all are looking for.

Keep in mind, humans are power limited. If we assume a monofin has 50% thrust efficiency and can propel a good fin swimmer at 6 knots in a sprint, raising the thrust efficiency to 100% will raise the swimming speed to only 7.6 knots (there is a cube-root relationship between power and speed). This would be the theoretical limit of performance gain without somehow getting more power into the system because attaining more than 100% thrust efficiency would violate the laws of physics. Whereas 6 knots has the potential to elevate a swimmers center of mass about 48 cm above the water, the extra 1.6 knots resulting from the increased thrust would only be worth an extra 3.5 cm of additional altitude in a breach. That is a mere 7% improvement in exchange for a doubling of the thrust.

However, lowering the drag does not have the same effective limit to speed because the drag term is in the denominator. Cut the drag by 1/2, and you get the same effect as doubling the thrust from 50% to 100%. But, it is theoretically possible to reduce the drag by more than 1/2. It could theoretically be reduced by 3/4 with appropriate streamlining, which would give you a maximum speed of 9.5 knots without improving the propulsive efficiency. Cut the drag by 7/8 and you would achieve 12 knots.

The bottom line is that, we should not expect any fin, no matter how advanced and efficient at producing thrust, to make a huge difference in how fast a finswimmer can go, without also addressing the overall drag of swimmer/fin combination as well.

 

[Bill]

I don't want to start something but this is the first time that I've heard about the 'cube root'. The formulae that I thought applied for a non planing form is

power=(K x velocity)^2 x weight with K being an efficiency constant

The square rule seems to work for bicycles and airplanes too.

 

[terrafugia]

OK, I see that I made an error in my math, but it was not the cube part. I treated something as linear that was not. The extra 1.6 knots would provide about 30 cm of additional altitude in the breach, not 3.5 cm. That is a 60% improvement for a doubling of the thrust performance. Sorry about the error.

Non accelerating motion:

Thrust = Drag = Cd*K*V^2

Energy = Thrust*Distance

Power = Energy/Time = Thrust*Distance/Time = Thrust*Speed = (Cd*K*V^2)*V = Cd*K*V^3

Cheers

 

[Fondueset]

The biggest drag reducer - along with an orca speed suit and no weight belt - would be a low amplitude/high frequency kick in classic monofin posture - of course slamming the arms for thrust just before they leave the water.

We were able to ascend with few kicks with the Lunocet but only at very high amplitude - essentially using the fin as a paddle. With that approach you'd essentially be working to kick yourself out of the water - rather that going ballistic by virtue of low drag and accumulated velocity > which are the two 'breaching philosophies' being presented here. I know for sure that fish use the ballistic approach and its also the approach I've seen dolphins use - that is - high oscillation/ low drag ballistic breach. (of course dolphins have more mass relative to fluke area than humans - and I think about 18% of that is muscle focused mainly on propulsion - not to mention streamlining)

 

[terrafugia]

What makes the Orca Speedsuit more streamlined than other wetsuits?

 

[Fondueset]

I don't know that there aren't better ones - but they are optimized for streamlining - and it is noticeable - in much the same way that a smoothskin suit is more streamlined than a nylon covered one. i don't think it would make the difference between breaching or not though and I think my phrasing is misleading - the biggest drag reducer, obviously, would be body position and small amplitude.

 

[terrafugia]

Regarding the issue of drag reduction, I’d be interested to know peoples thoughts on achieving better streamlining. How can we improve it and at what cost? Would it be acceptable to start adding fairings and gussets to a finswimmer to lower drag? If so, what are the practical limits, and how can it be done?

 

[trux]

I just wonder if anyone of you has any news about Lunocet? I see no news on the Lunocet website or blog since the Bahamas trip, so I wonder whether Ted works on improvements, or whether the feedback was more negative than he expected, and he has put the project to the backburner for the time being. Would be a pity, because I like the concept and believe it has a great potential.

BTW, Ted may be interested to know that Sporasub used their idea of bicycle shoes: http://forums.deeperblue.com/spearo-board/81011-spooo-raaa-suuuuub.html#post753280

 

[Fondueset]

Hi Trux - I just dropped Ted an email. We'll see what he says. I can see the cycling shoes working well on bi-fins - where drag is not such an issue. They are definitely comfortable, and would make for solid force transmission.

 

[trux]

BTW, I've got also email from the inventor of the DOL-fin mentioned earlier in this thread. He sent me a video and photos, and it looks also interesting (though probably less suitable for breaching, I'd tell). I am waiting for permissions to publish the photos/video - it was not clear whether he sent it to me for my personal information or whether I am authorized to share it with others, so I prefer waiting for the approval before putting it on my website into the Collection of Weird Fins.

 

[Fondueset]

I Trux,

We also tried the Dolfin in the bahamas. I'll pm you about it.