How to measure fins efficiency

[amihov]

I have been thinking about fins efficiency . I always have this feeling that some fins are very efficient on the surface and they loose their quality once when you are 5 meters down. I don't understand why the efficiency is changing. Water doesn't compress so it is not the water . The only conclusion is that long blade fins are poor on the surface because you can't make a full kick whit them .But when you are using them under water they are much better because you can move greater volume of water whit full amplitude. And short fins are efficient on the surface because they required less amplitude and you can achieve full kick whit them on the surface.

 

[laminar]

Water density does increase with depth, doesn't it?

 

[shoutatthesky]

I believe technique is far more important to the efficacy of a fin than the fin itself. Also different fins require slightly different techniques. I agree that long fins are no good for surface swimming(unless you use Eric Fattah's method of swimming on the side with an arm outstretched).

 

[shoutatthesky]

Like Amihov said water doesn't compress so how can water be denser at depth? Could temperature or salinity levels increase density?

 

[Bill]

Water density does increase with depth, doesn't it?

Good question. Does that 5 degree density rule that seems to be unique to water apply at the same temperature in salt water? Does the sun make the surface water more salty?
I guess in Vancouver there are other more important things, eh.

lol
Bill

 

[ncunuclear718]

I believe technique is far more important to the efficacy of a fin than the fin itself. Also different fins require slightly different techniques. I agree that long fins are no good for surface swimming(unless you use Eric Fattah's method of swimming on the side with an arm outstretched).

Please tell me more about Reic Fattah's method
or give me a link, Thanks!

 

[shoutatthesky]

http://forums.deeperblue.net/freedi...behind-ii-return-tahsis.html?highlight=tahsis

Post #8

 

[amihov]

I don't thing that the sun will affect the water so much. Salt water is more dense than normal water but that is not the case whit fin performance. I have 3 pairs of fins rondela cressi they are small fins good for the surface i never had problems whit them even in very cold water. But my Beuchat Competion is different thing. In the beginning i like the fins but the plastic stared to change its shape. After about 2 years they were not strait any more and when i use them in cold water the fin has bad response . Now i am using them only in the pool. It seems like plastic fins are greatly affected from water temperature . In the pool i can swim whit them and they are not as bad as in cold water. My last pair of fins witch i got about 3 months ago is C4 Flap carbon fiber. I have been very happy whit them water temperature is not affecting them at all. The bad thing about them is that you have to be very careful whit them the material is very fragile. For me the best combination is a pair of good plastic fins for shore dives around rocks and cabon fiber for deep dives. The problem is to find a good pair of plastic fins for cold water.

 

[shoutatthesky]

Two years out of plastic fins sound like a good run. Problem with plastic is it has a memory so they stay bent after some use. Your problem sounds like it has nothing to do with water temperature.

 

[amihov]

Yes they are bent .Plus in the pool they are better then in cold water. Now whit my carbon fins i am not sure if it is normal to have small like air bubbles on the fins surface. I have been taking care of the carbon fins but i don't remember if they were like this when i bought them . They have 2 years warranty maybe i should talk to the manufacture or to the company from witch i bought them from.

 

[laminar]

I agree that long fins are no good for surface swimming(unless you use Eric Fattah's method of swimming on the side with an arm outstretched).

Actually, that is a fairly common finswimming training technique.

I would guess that the change in perceived efficiency is actually more related to the massive buoyancy changes in the first 5m that require a slightly modified technique. I've never noticed it as such. I've always felt way more efficient at depth.

Yes, temperature and salinity relate to seawater density:
Ocean Motion : Background : Ocean's Vertical Structure

Here's a density calculator:
Utilities: seawater density

 

[Bill]

Thanks for the calculator. I'll have to plug in some numbers and check. Since fresh water reverses at about 5 degrees and becomes less dense with colder temperature. I've always wondered about salt water. Now I wonder if it's a 'fact' that wasn't true to start with, like so many others. ..... and while I'm rambling on, after the change of state at zero, where water looses over 10% of it's density, does it become more dense again as it cools?
Older and older, curiouser and curiouser.
Aloha
Bill
ooP.S. Before I'm accused of hijacking a thread, I have a pair of blue (soft) plastic blades that were my first purchase from a Kona dive store over 20 years ago. I've used them 500+ times and they haven't changed shape or feel much. I mounted them on my favorite Omer pockets briefly last year.

 

[trux]

Bill, have a look at this thread: http://forums.deeperblue.net/beach-bar/71544-unknown-water-post645914.html
The links may interest you and your questions will be on topic there

 

[Bill]

Thanks Trux. I read your post last week. The links were very interesting.
Aloha
Bill