Diving Performance - Beyond Drag (article Series And Discussion)

[REVAN]

I am using the exact same blades off my Aqueon, but in a much more efficient manner, being controlled by my hands, not a spring. Why wouldn't they provide propulsion?

If you articulate the fin properly, you can get some propulsion with it. I experimented with this years ago. It can certainly be used to change the dynamics of the monofin stroke, but all my testing indicated there was no net benefit from an efficiency perspective to using the front foil. I should caveat this with the fact that I am using the same basic fin both front and back, and the rear fin was specifically designed to work optimally without a need for a front foil (that is, it is balanced to not need a counterpoint beyond that of the diver's upper body). If I were using fins in the back that were less efficient than the front foil, then I suppose there could be something to gain from shifting some of the propulsion to the front. In my case, they were the same.

With my camera rig, I'm not using the foil for propulsion. It is just a streamline bar I use to hold the cameras out to the sides and steady. You can hold the cameras steady, or articulate the foil in counterpoint to a monofin stroke to generate extra thrust, but you can't really do both at the same time, and there is no counterpoint if you are doing flutter kicking.

Bottom line, the best use for the front foil I have been able to find is mounting cameras to it. If not for that, I'd much rather have my hands free to do other things during the dive. Unlike the DIR crowd, I like using my hands when I'm diving. I often find them useful.

 

[John C. Ratliff]

REVAN,

You know, a bicycle can be ridden "hands free" too. But by using the handlebars on a bicycle, you get more leverage on your legs.

The same holds true for the use of the front blades, that they provide stabilization to the dolphin kick and increase the force generated by the fins, while they also do provide propulsive force.

Do you have any trial evidence with data from your experiments, such as time or stroke numbers over distance to verify your observations?

Also, there is a reason for the loop in the line that connects the two blades. One is a slip knot that holds the blades together, while allowing to be separated for travel; the other is so the line can be looped around the hand, allowing the Hammerhead Unit to float out of the way when you want to use your hands to do something on the bottom, to take a photograph, to pick up something and put it into your BC pocket, to play with a crawdad or feed fish on the bottom, etc.

John

 

[REVAN]

Also, they do provide propulsive force.

Yes, but it is not free. It takes energy to do it and the conversion rate is no better than the fin on my feet (talking about my DOL-Fin monofin here). - Same fin, same efficiency limits.

I usually just let my camera rig glide in front of me, barely hold onto it and providing just enough push to keep it moving. It generates the lift to support it's own weight if I'm moving more than about a knot in speed (the camera rig is negatively buoyant). If I actually try to use it for propulsion, my shoulders get tired pretty quickly. You could probably build some serious upper body strength if you used it a lot for propulsion. The bodybuilding health markets are way bigger and more profitable than the diving market.

 

[John C. Ratliff]

REVAN,

This is conceptual only, as I'm not trying to market anything. The Hammerhead Unit would be built fairly easily by just about anyone. While I put together a "disclosure of invention," at this point I'm putting no effort into patenting it (though I do have about a year to do so if I wish). That was more an educational tool to show the concept.

Think of a humpback whale, with those massive pectoral fins. When that whale is in full speed swimming, they are folded away for streamlining. But when they are playing around, they are used for maneuverability.
Now, think about what any of these whales would be like without pectoral fins.

When I use the Hammerhead Unit, I sometimes use it for propulsion, I use it to make a very fast, hard surface dive, I use it to provide that propulsive thrust into a high current area, and to "glide" along the bottom, either with or against the current. Even when not used for propulsion, it stabilizes the body, and provides another "anchor" for the rest of the dolphin kick stroke.

I cannot help you concerning upper body strength, but realize that you're talking to a 70 year-old who is not a body-builder, who is using this to advantage.

For my videography, I use a GoPro that is helmet-mounted to get the video, and if I want some of me, I either take it off, or hold it to one side with my hand. I like your fin concept for this, but could not use it with the Hammerhead Unit.

I have some video I shot last summer, and I'll see whether I can get it back (had a hard drive crash) and put it together, but it may take a bit of time to do so.

SeaRat

 

[REVAN]

It will be interesting to try the streamlined kit with the monofin at some point and see how much improvement there is over the James Bond video configuration. Right now the pool is too cold to bother with any testing though. I figured that no one else was going to care about doing things with monofins, so it was a low priority that I decided to put off until June. I also figured that a front monofin would be even less appealing to scuba divers than having a DOL-Fin monofin in the back. That's why I have not pursued anything with it beyond using it for getting my videos.

 

[ronscuba]

Many internet arguments focus on differences vs. Similarities.

I don't agree with everything revan says, but it should be safe to say most divers would like the ability to go faster or the same speed with less effort.

What we are willing to do to go faster is different for each of us. Streamlining your gear is pretty simple and cheap. Improving kick technique is free. Getting new fins is something most divers do in their diving lifetime.

I just got back from Cayman Islands. 3 divers had new fins. They all were happy saying they could go faster and with less effort.

That turtle, grouper or stingray that is 60 feet away ? I could swim over to it for a closer look or sit and hope it swims to me. Nice to have a choice.

 

[REVAN]

What we are willing to do to go faster is different for each of us. Streamlining your gear is pretty simple and cheap. Improving kick technique is free. Getting new fins is something most divers do in their diving lifetime.

It can be cheaper. BCs usually cost $300 to $500, but a simple harness is usually closer to $50 and streamlined.

It's no secret that I'm not a fan of BCs. The soft bladder is the worst possible solution to buoyancy control that I can imagine. They are unstable in the water column and most divers would have better buoyancy control without them.

Between the drag penalty and how badly they work, I have a hard time understanding why everyone thinks they need to use them. As I see it, a BC is a piece of specialty equipment that is not appropriate to use on every dive, only some dives where they are more good than trouble.

 

[ronscuba]

I thought the purpose of the bcd bladder was to offset the buoyancy changes of a wetsuit as you go deeper and the tank as air is used.

As long as those 2 changes are present, we will need a bcd. It is possible to minimize that buoyancy change and then use a smaller bladder.

 

[REVAN]

I thought the purpose of the bcd bladder was to offset the buoyancy changes of a wetsuit as you go deeper and the tank as air is used.

As long as those 2 changes are present, we will need a bcd. It is possible to minimize that buoyancy change and then use a smaller bladder.

Your lungs have plenty of capacity to do both of those things unless you are diving more than 3mm full body suit. Beyond 3mm, it can still be done, but the planning has to get pretty good to pull it off. With a 5 or 6 mm suit, you need to know the target depth and set your weights for within range at that depth. For people who dive shorties, or no wetsuit like you, I honestly think a better dive experience can be had if the BC were left at home. It's not hard to figure out your weighting, and once it is right, it is just right. There is nothing else to mess with. Just swim and enjoy the dive.

Everyone thinks that I'm going to be crawling on the bottom because I have no BC. They are always surprised when I demonstrate better buoyancy "control" than everyone else in the group.

 

[sea_ledford]

But without a BC crappy instructors can't overweight the students to keep them on their knees during skills. And they'll NEVER be able to do a fin pivot!

Now all this talk of swimming 5 knots is one thing, but no BC!!!?? Blasphemy!

One of my favorite classes to teach is buoyancy control. First step- take away all of everyone's weight. Step two - go diving. Of course steps 1.1-1.9 are arguing about how much weight they used to use, or have to use or want to use.

-Chris