Improving trim?

[lowwall]

I *think* I need to determine the right amount of air to add to my BC but I can't seem to find that ...
Help?

The amount of air to add to your BC is just enough to make you neutrally buoyant. Trim is what happens when you are neutral and stop moving.

So what happens at depth when you are neutral and stop moving?

Next question is what kind of BCD and how much weight do you have? BCs with large lift capacity can make holding a desired trim difficult as the air moves around. The weight is because I'm trying to figure out whether to recommend a steel or aluminum backplate to replace your BCD

 

[Marie13]

I'm a 5'3 shrimp
But surely, there's a way to move weights around so it works?

I’m 5’5” and a HP100 was almost too big for me single tank.

You should see about trying a smaller tank. A HP80 would be ideal. They are nice little tanks for us shrimps for single tank diving. They are about 4” shorter than a HP100.

Sometimes gear doesn’t work for you and you have to try something else.

Know someone who is 4’11”. AL80s are too big for her. She has to dive AL63s.

 

[Wibble]

Wonder if your air consumption will improve with correct weighting and trim. Your SAC (Surface Air Consumption) will get much better as you get used to diving and become more comfortable underwater. Being overweighted and out of trim will definitely mean you use more air.

Generally speaking, smaller people consume less air -- simply because there's less mass.

Smaller tanks could be better for you as they may reduce your SAC.

 

[Scott]

I'm a 5'3 shrimp
But surely, there's a way to move weights around so it works?

Sometimes we make poor purchasing decisions that no matter the effort put in to making them work, it just doesn't.
My wife is 5'3 also and the only time she uses an AL80 is on vacation. For local, she took over a pair of LP80's I had and those fit her perfectly. For teaching it's an AL63.
I would really consider trading someone for another cylinder if possible or selling the 100 and buying something else, a HP80 as Marie mentioned. See if a another diver has another cylinder you can try. You might be surprised at the difference.

 

[lowwall]

Sometimes we make poor purchasing decisions that no matter the effort put in to making them work, it just doesn't.

Agreed. I suspect swapping the BCD for BP/W may help more then swapping an HP100 for an HP80. But it's a lot easier to test the HP80 hypothesis since you can just rent a tank. It would also be a cheaper fix given the resale value of HP100s.

 

[formernuke]

If you decide to sell the 100, let me know. At 6'2 they are my preferred single tank tanks.

I would highly recommend renting a steel 80.

Reminds me of many many years ago when a 5'5 guy couldn't wanted to use HP 120's.

 

[Marie13]

If you decide to sell the 100, let me know. At 6'2 they are my preferred single tank tanks.

I would highly recommend renting a steel 80.

Reminds me of many many years ago when a 5'5 guy couldn't wanted to use HP 120's.

Can steel 80s be rented in your area?

 

[Moerae]

I think a lot of people are waaaay jumping the gun talking about trim, changing tanks, etc etc.

To compensate, I add some air to my BC....

....I *think* I need to determine the right amount of air to add to my BC but I can't seem to find that ...

This sounds a lot less like OP needs help fixing trim and a lot more like OP needs an overall lesson on weighting, buoyancy control, and then trim.


As a first step, are you weighted correctly, @alex_can_dive?

Trim is a lot harder to work on if you're over-weighted.

Have you done a weight check at the end of the dive with roughly 500psi @ roughly 15ft (this means checking that you are neutrally buoyant at 15ft with 500psi in your tank, and zero air in your BCD, and minimal air in your drysuit if you use one)?

Can you hold a neutrally buoyant position and adjust up and down with your lung volume?

Do you have an instructor you're working with you can talk about buoyancy with? Maybe get a pool session in?

 

[formernuke]

Can steel 80s be rented in your area?

East coast divers had them pre covid not sure now that they have remodeled.

I'm not not sure which part of the state the OP lives in.

 

[formernuke]

I think a lot of people are waaaay jumping the gun talking about trim, changing tanks, etc etc.



This sounds a lot less like OP needs help fixing trim and a lot more like OP needs an overall lesson on weighting, buoyancy control, and then trim.


As a first step, are you weighted correctly, @alex_can_dive?

Trim is a lot harder to work on if you're over-weighted.

Have you done a weight check at the end of the dive with roughly 500psi @ roughly 15ft (this means checking that you are neutrally buoyant at 15ft with 500psi in your tank, and zero air in your BCD, and minimal air in your drysuit if you use one)?

Can you hold a neutrally buoyant position and adjust up and down with your lung volume?

Do you have an instructor you're working with you can talk about buoyancy with? Maybe get a pool session in?

I tend to agree with you in general hence why I asked if the OP had done that check.

With that being said hp100 and 5'3 is not a good combination.