Saturday, August 22, 2009

Missing link and side rail experiment

Sorry guys - I appear to have a missing link - must have 4gotten to put it in - will do so on Monday - do not have it now.

I did a little experiment last nite - I put side rails on the blades of my picasso carbon fins - I want to see how effective they can be. Apparently one can get up to 20 % efficiency increase - I would be happy with 10%. The C4 ranges have side rails. Only, when I think about options there are a lot of factors to consider:
Will the side rails inhibit the flexing of the carbon?,
How high should they be?
What is the optimum shape i.e. should I taper them?
Mine are only 1.5 cm above each side of the blade.
Should I shorten the footpocket rib and replace with rail?
What dampneing effect will they have on lateral movement of the fin.
How long will they survive the contacts with the bottom?
I used a windscreen rubber from which I cut a suitble section to make the rails.
If anyone has experience or has info on side rails please pass it on to me.


Volodya said...

Hi, Gletwyn,

I've been thinking a lot, drawing and.. even doing some side rails on my fins...
Rails help prevent water flowing from the zone of increased pressure to the zone of decreased pressure. That flowing occurs all the time, changing direction as we move our legs.
I also believe one can increase efficiency (save oxygen)by putting proper side rails on the blades... I think the outer wall of the rail should be flat and smooth. Their exact height can only be determined by very expensive experiments... At my level of 'craftsmanship' I use OMER's rails that are sold separately. Since they resemble C4's rails and both have the wrong shape, I cut the outer part of the walls which are to be glued to the blade and fix each piece separately, so that if one looks along the rail he sees a flat outer wall. I am sorry, I can't upload a drawing.
Yes, the rails somewhat stiffen the blade, not much. Yes, they consume some energy too, since they are made of rubber...
Given the discussed construction, the inner part of the rail curls each time the blade bends. This worsens the shape - a little - and prompts for a different construction.

Their life-cycle is not of much concern 'cause they're cheep.
I believe the height should be about 2 cm on each side, provided they don't curl much.

Now the bad part: trying to improve the performance of my Leaderfins carbon fins I started gradually shortening the footpocket ribs and adding side rails... My fins became much much better - more flexible and smooth... until one day one blade broke right at the bended zone! Then I saw that my blades only have one thin layer of carbon on each side but were mainly made of fiber glass... The footpocket ribs which I finally removed, strongly supported the blades and only allowed them to bend at small angles - not more than 10-15 degrees. As they were 2 mm thick the carbon yarn stretched too much. etc.
Yes, a friend or mine also used windscreen rubber, very cheep. I believe its height is not enough, and its shape - on the outer side is not the right one.
I would also like to get any advice on the subject.

Greetings: Volodya

Gletwyn Rubidge said...

Hi Volodya - Thanks for your comment - it certainly is of values am may save me much time in my experiment. I tried my carbon fins Spierre one with rails the other without - it was very stable compared with the other and felt more efficient but I must trest in the sea - fortunately my dive buddy has the same fins as me so comparisons can easily be made.
From what you say mine are wrong in that the side rails are 1.5 cm high and rounded - convex on the outside - I will post pics later in the week.

Volodya said...

Hi, Gletwyn,

Yes, side rails stabilize fin strokes and prevent them from going astray... but they do not prevent us from contracting the wrong muscles that make the fin go astray...
So maybe it is good to practice with no rails and then go deep down using them...?

I've been thinking on the construction of side rails that will do the job - channeling the water and preventing water-flowing from high to low pressure, without changing the strength of the blade...
I believe I invented a rather complicated form of very small side rails that inter-cover each other during bending and do not curl... Now I need someone crazy enough to start producing them...