Fin weight

[nivla80]

Hi guys,

I have no idea where to post this, so hopefull this is the correct place.

Just wondering, does fin weight play a part in being in perfect trim i.e. remaining horizontal in water with bent knees? I dive apollo XT splits, which are pretty heavy.

I believe i have my weight configurations right. No lead in a SS BP in a 3 mm wet suit, but as soon as i stop finning, my body tends to go to a vertical position itself. It is annoying as hell, as I have to consciously and constantly fight to keep myself in a horizontal position. Any input will be greatly appreciated!

Thanks!

 

[spectrum]

Fin buoyancy is a huge variable since it is out at the end of your body. Picture yourself as a see-saw. That is why bending your knees concentrates your center of gravity and helps.

One way to look at the equation is to say that instead of heavy feet you have a light chest. Since you have no weight belt the remaining easy option is to run your cylinder higher on your back. What do you use for a cylinder?

Pete

 

[The Kraken]

Actually, the specific gravity of the fin is of more importance. It's not so much about how much the fin weighs as it is a matter of its weight and its volumetric water displacement.

I'm sure length will come into play, but not as a major factor.

the K

 

[nivla80]

i don't own tanks, and when i dive, it's usually off dive boats, and i believe most ops use AL 80's.

Spectrum, I tried bending my knees, but still end up being vertical. And if i run my tanks even higher, I'm gonna get a concussion from crashing my head into the valves. It's about as high as it can get now, as in my head is already touching them.

Kraken, i don't really understand what you're trying to put across. Care to elaborate?

THanks guys!

 

[spectrum]

Kraken is correcting your use of the term fin weight, just as I did by using buoyancy. Once in the water weight is irrelevant but specific gravity will yield buoyancy.

When you say you go vertical do you mean feet down?

What is your build? If you are stout then an AL80 can be a problem. It is a moderately long cylinder and has a fairly thick heavy bottom that will act as a tail weight.

Pete

 

[ronbeau]

i don't own tanks, and when i dive, it's usually off dive boats, and i believe most ops use AL 80's.

Spectrum, I tried bending my knees, but still end up being vertical. And if i run my tanks even higher, I'm gonna get a concussion from crashing my head into the valves. It's about as high as it can get now, as in my head is already touching them.

Kraken, i don't really understand what you're trying to put across. Care to elaborate?

Thanks guys!

Have you considered mounting your first stage with the turret pointed down to give yourself 3 more inches of clearance? By mounting you first stage with the turret point down the first stage does not stick up above the valve by much at all.

 

[nivla80]

I'm 5'9 and 132 lbs...

Kinda underweight, i guess..

 

[spectrum]

Mmm that's pretty much my height, but not my weight!

If you can get your hands on a Steel High Pressure 80 to try I bet you will like it.

Those split fins are open heel style worn with booties, right? My fins alone are negative enough to offset my booties buoyancy.

 

[nivla80]

I wish i could, but most dive ops dont offer steel 80's, and besides, i will be way too negative...

Well, i'll see if i can maybe pop a couple of trim weights on my cam bands.. Thanks for your help anyway!

 

[rakkis]

Try attaching your wing further back.

Think of trim underwater as a teeter-totter. Lift from your air bladder and lungs brings your head up, badly placed weight brings your feet down. By moving your wing a little closer to your belly button (away from your head) or moving weight a bit closer to your head (for example, attaching your tank an inch or two closer to your head) you will bring your center of buoyancy closer to your center of gravity...thereby making it easier to get a horizontal trim.