building a serafinocet

[serafino]

I've hit a major problem . The bolts I need don't exist. I don't have a machine shop that I could make them with either. I guess I'm gonna need to find another way to attach them to the rod. I may need to use bicycle crank arms and chop them up since they have the right threading. The problem is this solution requires more aluminum welding and the semester just finished and I don't have access to the welding machines for a while. Man I never expected this many problems on such a small build.

 

[Salehthefish]

hey mate

Try to use rivets or clamps if there is a way to make it in such a way clamp would do...

Would recomand that your design to go in this way:

1- Design and write it down on paper...
2- Chose materials, parts and check for availability...
3- Once everything is ready then you can start assembly ( Keeping in mind that some joints should be permenant and some would be temporary)
4- Then you will edit some points because you will never find perfect design...
5- Finishing

Better to check some topics on general design would be more helpful...

Anyway photos showing nice work and wish to see it finished soon...

 

[ahofbauer]

Hi there!

My Name is Max, therefore my wing should be called "Maxocet"!

The approach i used is slightly different:
There is a stiff winglike foil and also a pair of footpockets, as well as an adjustable
reaction spring and a flexing point. The difference is, that it is rather a low tech
and low fuzz approach to the problem.

both fins.jpg

I used normal footpockets and inserted them into a stiff wing i carved
out of a piece of hi density styrene. The wing is made of 6 layers
(each 3mm thick) that have been glued together leaving the openings
for the fin-blades. The Flyer-Monofin is there just to show the size.

dowels.jpg

The assembly is being held together by the means of four dowels made
of half-inch plexiglass bar-stock. (no glueing, so it could be disassembled if neccessary)

edge on.jpg

The profile is a symmetrical wing-shape, with some allowances regarding the "not so sharp" rear edge, it´s less dangerous and it doesn´t break off so easily.

springs.jpg

The rubber footpockets are too soft and dont´s transmit the force well, so it was neccessary to add two changeable fiberglass springs (white color) and swim a lot of trials to find out the correct config.

ribbon.jpg

These springs must be tied to the ankles in order to transmit the power correctly. This is being accomplished by velcro-straps.

The fin is really heavy when out of the water because it has about the same specific weight as water... but IN the water it is neutrally bouyant.

The only problem it the constant "croac-croac" sound that is produced between the foot pockets and the springs
I obviously haven´t tried a Lunocet, but my wing works quite fine. The wing surface, however, is slightly too small.
The wing is 80 cm wide, 18 cm long and 1.8 cm thick in the middle.

Good Air People!!!

 

[Kars]

I would love to see a video Max!

Is the blade at the perfect propulsion angle during most of the stroke?

Love, Courage and Water,

Kars.

 

[Salehthefish]

hey man nice and simple design excellent

Wish i would have time to work on any design like those...

all best

 

[ahofbauer]

Hi!

Right now I´m kinda far away from home, it´s something
that happens to me from time to time (anytime I work).
Hopefully that will change by the end of january.

Well, so much as for the video...

About the angle:
The angle is not that perfect, because the springs "come
out" of the sole and I haven´t had time to laminate some
"bent" springs to correct the defect.

But I discovered something I consider of PARAMOUNT importance:

The mere fact of using springs in order to control the angle
of attack of the blade, automatically defines the attainable
top speed, i.e. limites the speed.
That happens because the more power You put into the fin,
the more the springs flex and the steeper the angle of attack
becomes.

Remember:
A steeper angle means more "torque" and less speed.
Just great if You try to pull something underwater, but less
than ideal if Your quest is for speed!

...ever wondered why dolphins have that big pack of muscles
where the fluke connects to the tail?
That´s because they must conteract the tendence to "overflex"
the blade.

 

[ahofbauer]

Hi!

I´ve been toying around with the idea of
perfecting a springless fin.

Ideally, the blade would be attached to the
footpockets by some kind of hinge and
feature angular stops to limit the movement.

My current experiment uses (as the pics show)
a flexing point that is far ahead of the blade´s
centerline.
That means that the blade´s position is neutral
both at the top and the bottom of the sine-wave
described by the dolphin kick. It takes some
forward travel to flex the blade to a point where
propulsion is accomplished again.
That means that both the cusp and the bottom
of the sine-wave are useless for propulsion and
only the up and down strokes generate trust.

...about 50% of the complete power-input is
being lost...

After that much testing, it seems that the correct
flexing point should be at the blade´s centerline.
Because of the semi-ellyptical shape of the blade,
the surface is bigger behind the centerline and
causes the blade to "flip" over as soon as the stroke
changes it´s direction.

This very fast reversal in the blade´s angle at the
end of the stroke saves time.
The final result ist that the pauses at the stroke-end
become shorter. Possibely a relation of 70% power
to 30% pause could be attained.

Notice:
I´m not so much of a deep-diver as a fast-diver,
sub-surfer and breacher.

 

[serafino]

Hey guys been a while since I found some time to work on my fin or even come online. I found a solution the problem is I need a TIG welding machine which cost around 8,000 bucks. I'm waiting until the welding class starts up again this spring semester. Since I can't find a bolt I'm going to the bike store to buy aluminum bike crank arms since they already have the right threads. Then I'll chop em up and weld them to the rod I have.
Hopefully it will work.

Ahofbauer nice looking fins. I disagree with your springless is better. What you need is a combo. You need flexible resistance either springs or someother means and a stop to keep it from going too far. Dolphins are actually what I am basing my fin design on. They have huge muscles as you say so they can hold the desired pitch in their fin. It is very flexible if you have ever held a dolphins fin. The muscles are the stop which keep it from pitching too far.
Best of Luck,
Serafino

 

[ahofbauer]

Hi!

I fully agree with You...
...but in this case we´re trying to
"dolphinize" a human being (meaning: no muscles at all)

 

[serafino]

Sorry guys I have been so busy with everything lately I haven't even been able to think about freediving and my monofin. I have been extremely busy with free running and traveling. I will get this fin done. I'll finally have some time to work on it this month. I'll definitely make some progress and I'll definitely still finish my project. I'm not giving up easily.

 

[serafino]

Just an update I'm nearing the completion of the fin I have been busy with school lately and a sponsorship for another activity and they have had priority. I've just started working on it again and I'm almost done!!! I have a few things left to do but I'm not giving up!:martial