Buoyancy of fins & the effect on horizontal trim

[SouthSideScubaSteve]

This may be a little drastic, but switching from a typical BC to a BP/W can help with trim. A BP/W will put more of the weight on your back rather than hips which is one of the causes of bad trim. I also struggle with being feet heavy and I have yet to be able to solve it, I dive a Zeagle Stiletto by the way. I have not completely solved the issue but I have got it to where I'm not as feet heavy. I haven't gotten to the point to where I want to switch fins yet but it certainly could help if you have heavy fins.

I don't know the Stiletto, but I dive an Aqualung Black Diamond (back inflate). What you say makes sense, but I guess I was thinking that new fins would be cheaper than getting rid of my BC!!

On my last dives in salt water I was wearing a 3mil John & LS-Jacket (I figure it works out to being the same as waering a 5mm fullsuit from a bouyancy standpoint) and had 10# in the trim pockets (right behind my shoulder blades) and 8# in the ditchable pockets just above my hips ... maybe I should try moving a couple more #'s off my hips to see what happens.

 

[ae3753]

So you are saying that the buoyancy effects from the fins are negligible compared to the effect on my CoB by straightening my legs?

Yes. Body position has a significant impact on balance and trim.

You state that you are horizontal while frog kicking, and out of trim while fluttering. The biggest difference between these two positions is leg position.

 

[InTheDrink]

Differences in fin buoyancy aren't all that significant. They can be overcome with leg positioning (i.e. lever arm).

Hmmm, they're different enough to make a difference, from my limited experience.

Since getting Jets (which I love but might consider swapping for similar but less negative brands) I've had to move my tank up and extend my arms (superman) to keep decent trim.

No biggie, but there is definitely a difference.

J

 

[Vlane]

I don't know the Stiletto, but I dive an Aqualung Black Diamond (back inflate). What you say makes sense, but I guess I was thinking that new fins would be cheaper than getting rid of my BC!!

On my last dives in salt water I was wearing a 3mil John & LS-Jacket (I figure it works out to being the same as waering a 5mm fullsuit from a bouyancy standpoint) and had 10# in the trim pockets (right behind my shoulder blades) and 8# in the ditchable pockets just above my hips ... maybe I should try moving a couple more #'s off my hips to see what happens.

When I dive wet I use 10# and 6 of those I put in the trim pockets on my upper cam band. Even with that and my tank up fairly high I still slowly float feet down, but not near as bad as before. I think I have my my trim as good as it's probably going to get while diving wet without switching to a BP/W or switching to a frog kick. Right now I'm making the transition to diving dry and I'm fighting a combination floaty feet and sinking feet as I figure out bubble management.

 

[Randy g]

Try positioning your arms under your face or extending them forward with one hand holding the opposite wrist. It will move your CoG forward, moving your head down and feet up.

Kevin at UE did a peak performance bouyance class with us and completely changed the way we dive now. He showed us the difference in arm position in relation to horizontal positioning. It works!

 

[kanonfodr]

When I dive wet I use 10# and 6 of those I put in the trim pockets on my upper cam band. Even with that and my tank up fairly high I still slowly float feet down, but not near as bad as before. I think I have my my trim as good as it's probably going to get while diving wet without switching to a BP/W or switching to a frog kick. Right now I'm making the transition to diving dry and I'm fighting a combination floaty feet and sinking feet as I figure out bubble management.

^^^^:classic:
I did my first drysuit dive this Friday and I must say, that will cure your foot-heavy problem as soon as you end up getting a bunch of air in the legs of your suit.

Back on topic, what you do with your arms has an effect on your trim as well, I see most of the dive guides around her keeping their hands tucked under their arms, looking as if they were a little chilly. That would be one solution to keep you trimmed, but I am personally working on my frog kick as, once you get a good grasp of it, it works a lot better than the regular flutter kick. Less muscle use, which leads to less air use, and also doesn't run the risk of silting up the joint like a flutter kick can do.

Peace,
Greg

 

[HenrikBP]

I'm with Vlane; I put XS Scuba pockets on my cam bands and moved some of my lead from the belt to the cam band pockets. That helped a lot with my trim in general. It gives you more options for distributing whatever weight you need to help your trim.

Henrik

 

[Mayor]

Funny, I was in the pool today doing a weight check with another member. He uses a Steel backplate (6lbs) and STA with weight (6lbs). His feet were very floate so I pulled his fin off and it was negative. Hummmmmm. We moved some weight to the lower cam band and he was good to go. It was more of an issue with the AL80 then the HP100. He will have to pick up two small pocket to put one pound each in. That's all it took to make things right!

Everyone's body is different and has different weighting needs. Can't beat a few hours in the pool to fine tune your set up.

 

[ppo2_diver]

I use Scubapro Jets and haven't felt much of a difference from my "pool" fins. Much of it will come with experience. New divers may have not gotten their "swimming" legs yet and are not aware of their leg positioning. Try switching to the frog kick and put as much of your weight on top of your center of gravity as you can. Like others have said, I put my weights on tank band pouches.

 

[ae3753]

Yes, I use an AL80 (I got a great deal on a couple when Gander Mtn got out of the scuba business)... Any idea at what pressure an AL80 goes Positive?

It occurs to me that my problem typically gets worse as my dive goes on... I'm now wondering if I have my tank too high up and my tank is lifting my head & shoudlers up as the dive goes on???

Perhaps, but AL80s go butt light, when they become more positive.

Most people have the sensation of being feet light at the end of a dive with AL80s.

Depends on the AL80, but they are around -4#s at the beginning and +2#s when completely empty. Based on those number, it's around 1000 psi that they are "positive." However, they become less negative as you start using the air in the tank, so the tank effect will be felt sooner.

Oh, since you're in the Chicago area, reach out to Duane/pp02_diver. Internet assistance is okay, but getting help in person is significantly better.