BP/W: I officially don't get it

[Adobo]

Picture #2 could have an HP130 on his back and look the same. Maybe a puff of air in the wing at the start of the dive. The tank does have some effect but in this case it is a non issue. The OMS slipstreams are neutral in the water and I would guess the Aqua Lung blades are positive. They are not negative for sure.

Yes training and time in the water has a lot to do with it but can you trim out a jacket style BCD as easy as a BP/W?

Generally speaking, steel tanks are negative when empty and aluminum tanks are postive when empty. That means that properly weighted, a diver generally has more lead to carry when diving aluminum tanks. And that means more lead that the diver can distribute anywhere on his/her body to achieve horizontal trim.

The fact that the fins in pic2 are less buoyant than the fins on pic1 illustrates that weight was in fact distributed differently in pic2.

Again, there is more to it than simply going from rear inflate bc to backplate. I cannot speak for jacket bcs as I have almost zero experience with them.

It might just be that the most significant change here is not the gear but the knowledge of the diver.

 

[Sas]

Yes training and time in the water has a lot to do with it but can you trim out a jacket style BCD as easy as a BP/W?

I can trim out in a jacket style BCD if needed these days just as well as my BP/W. However, in earlier days, my trim was much better in a BP/W than a jacket BC. I find a BP/W helps to compensate a bit for poor skill, at least in my case These days the main advantages are that I have been able to drop 4lb from my weighting (due to the buoyancy of my old BC) and 6lb has been transferred from my weight belt to the steel plate. It is also more stable and does not move around like my old BC did. I like the harness better (I have had a Q/R break so prefer one piece harness) and I like it not having dump valves and d-rings all over the place. Also it is cheap to replace parts as it is modular. But helping with my trim, well not really an issue now, other than it is more stable but even with an unstable BC I can correct my trim quickly...

 

[Mayor]

Let me ask you this. Would a single tank adapter with 6lbs weight added make up for the alum 80 changes during a dive. If we really want to get into tank changes we should also find out what the tank psi were during the dive. Was this shot taken with 2800psi or 800psi?

The Aqua Lung fins are positive but his feet are still down?

 

[Adobo]

I am not in any way opposed to the use of backplates, but to the idea that there isn't any sensible alternative. I suppose I am fundamentally opposed to the prescriptive DIR/GUE approach, and much more attuned to the more relaxed "laissez-faire" approach of the training I had.

I have no idea how DIR or GUE got roped into this discussion. I thought we were talking about the merits of backplates and BCs.

 

[Mayor]

"The main thing your missing in this thread is the BP/W needs some time to adjust and get it right. Might take 2-20 dives to get it set up right. This should be done with a instructor / dive master to fine tune everything. Think of buying golf clubs off the shelf or getting a custom fit. This is a huge difference and you have to make a commitment. A little time and effort up front will pay off in the end."

I posted this sometime ago in this thread. IMHO you can never get the level of trim and control in any jacket style BCD that you can in a BP/W. Now that's just my thinking and it's not worth much.

 

[Mayor]

I can trim out in a jacket style BCD if needed these days just as well as my BP/W. However, in earlier days, my trim was much better in a BP/W than a jacket BC. I find a BP/W helps to compensate a bit for poor skill, at least in my case These days the main advantages are that I have been able to drop 4lb from my weighting (due to the buoyancy of my old BC) and 6lb has been transferred from my weight belt to the steel plate. It is also more stable and does not move around like my old BC did. I like the harness better (I have had a Q/R break so prefer one piece harness) and I like it not having dump valves and d-rings all over the place. Also it is cheap to replace parts as it is modular. But helping with my trim, well not really an issue now, other than it is more stable but even with an unstable BC I can correct my trim quickly...

We should do a dive together so you can change my mind.

 

[Adobo]

Let me ask you this. Would a single tank adapter with 6lbs weight added make up for the alum 80 changes during a dive. If we really want to get into tank changes we should also find out what the tank psi were during the dive. Was this shot taken with 2800psi or 800psi?

The Aqua Lung fins are positive but his feet are still down?

Actually, all the tanks I have ever dived have gotten more butt light at the end of the dive than at the beginning.

With regards to fins... if you are feeling head heavy (meaning that when you try to achieve horizontal trim), one of the ways to compensate is to dive with your head up and your knees down. You also bend your knees as extending your positive fins out further exacerbate the feeling of being head heavy.

If you then switch your fins to something more negative (or in this case, something that is neutral as opposed to positive). You balance out some of that head heavy feeling as the fins serve as a counterweight. You can then assume a more horizontal posture and even extend your feet out.

In this case, I don't know that the difference between the two fins the diver was wearing was significant enough to have caused any of the trim issues in the first pic but conceptually, changing the amount of buoyancy (positive or negative) does have an impact on the divers trim.

 

[Mayor]

Actually, all the tanks I have ever dived have gotten more butt light at the end of the dive than at the beginning.

With regards to fins... if you are feeling head heavy (meaning that when you try to achieve horizontal trim), one of the ways to compensate is to dive with your head up and your knees down. You also bend your knees as extending your positive fins out further exacerbate the feeling of being head heavy.

If you then switch your fins to something more negative (or in this case, something that is neutral as opposed to positive). You balance out some of that head heavy feeling as the fins serve as a counterweight. You can then assume a more horizontal posture and even extend your feet out.

In this case, I don't know that the difference between the two fins the diver was wearing was significant enough to have caused any of the trim issues in the first pic but conceptually, changing the amount of buoyancy (positive or negative) does have an impact on the divers trim.

I just thought we could have some fun with the pictures. After this PADI Dive Master candidate program I really want to take a few GUE classes. Can't wait to see if my skills are up to par.

 

[Mayor]

I have no idea how DIR or GUE got roped into this discussion. I thought we were talking about the merits of backplates and BCs.

Sorry, I might have said DIR but really should have said HOG.

 

[Sas]

We should do a dive together so you can change my mind.

Give me a yell if you are ever in Melbourne