Hi guys,
Interesting thread. The problem I see is that the market for monofins is really not large enough to justify the expense of trying out certain concepts in controlled conditions - unless you like really expensive hobbies! :duh
I've been thinking about monofins for a long time, tried out many different kinds, although none of the really new ones.
In my mind, these are the important points I would like to see address by a new design:
1. Asymetrical foil on upstroke and downstroke: I think most monofin designs work okay on the downstroke, but the upstroke acts like a brake at worst, or generates little lift, at best. I believe that mammals with fins get propulsion out of both upstroke and downstroke. True, trained finswimmers can get propulsion on the upstroke, but that costs extra energy for a freediver.
2. Clean leading edge with optimal angle of attack: The problem with the monofin in its current incarnation, is that it's attached to a person's feet, which, while they are flexible, are nothing when compared to the thinner shaft of a whale or dolphin's tail stem (or whatever you want to call it). I can't say for sure, but I would guess that when a whale moves its tail through the water, the leading edges of the fin are able to act on fairly undisturbed water (I'm assuming that's optimal - I may be wrong). This would allow the whale or dolphin to adjust the angle of attack of the fin for maximum thrust or max efficiency, depending on its needs. When I wear a monofin, I get the feeling that despite all my training, I'm stalling the fin at the beginning of each downstoke and throughout the upstroke. Usually the top part of the monofin around and under the footpocket is super stiff relative to the rest of the fin, meaning that it doesn't achieve the proper angle of attack needed for optimal lift and thrust. We need to get the leading edge of the monofin away from the body, like in the Aqueon, but perhaps it doesn't need to be so extreme and "in the way." I'm thinking of a concept that would create a "whale tail stem" for us humans that would put the monofin in front of our bodies and slightly below, giving it undisturbed water and the ability for us to control the angle of attack.
3. Less Turbulence: Obviously, a monofin that is flat at rest will create turbulence as you begin and end each stroke. A whale/dolphin tail is curved in 3-D. The edges of the monofin also give turbulence. You need a fin that has different thickness and flex characteristics as you near each edge (see windsurfing sail design musings below)
4. Form drag. Either you can create a flexible nose cone and stick your head and arms in it to reduce frontal resistance , or create a super efficient fin and swim much more slowly and more relaxed (like a Whale). I think most of us want something in between, but perhaps that's not the best way for us to swim. Think of how efficient no-fins really can be, just using our arms, we cover 3-5 meters of distance with one stroke. Yet, with a monofin we have to build up a stroke frequency to get going and really pay attention to reduce drag so we don't waste the energy.
5. Lift to mass ratio. I think we can safely say that the monofin is hugely inefficient compared to our marine mammal cousins when you look at the relative size of our fins. Dolphins have a tiny fin, but can go so fast. A blue whale is 100 feet long, and has a small fluke in comparison. But both have amazing body mechanics and musculature to make it all work. A monofin is between 1/4 and 1/3 our body length and twice as wide in some cases, yet we suck. Partly this is because our muscles and skeleton aren't set up for active streamlining. But also, I think, because we are not using the monofin in the right way for our limitations. It's not how big it is, but how you use it.
I think we can learn a lot from windsurfing sail design. The modern windsurfing sail, when powered up, uses battens and less often nowadays, cambers, to lock in a certain foil shape to create lift, even during lulls. In gusts, the head of the sail (the narrow part at the top), twists, flattens and loosens to allow wind to easy slip from the sail without causing tubulent drag. The battens in the sail have different thicknesses along the width of the sail to keep the overall foil shape consistent from luff to leech. So this means that you can configure a sail to be very powerful in light wind to get you going and then also still work very well when overpowered by not creating too much turbluence off the leech (trailing edge).
This could be applied to the monofin. I would expect if you could get the materials right, each stroke would be slow and drawn out, perhaps taking 2-3 seconds to complete, creating lift/thrust throughout the stroke. The centre of the fin would be thick and fat for lift and the edges would easily align with the water flow coming off the centre of the fin. If you wanted to go faster, you could shorten the tail stem and increase your stroke frequency and adjust the tension of the monofin to maintain its shape under higher load pressures. Possibly, the fin would be quite small relative to current designs.
These are exciting concepts I would like to apply to the monofin and try out some other revolutionary designs. I have lots of ideas on how to do it. Anyone have $10,000 they want to invest in my new monofin project?
I'm serious.
Pete
