Are you all just technical? What is technical?

[Fish-R-Man]

My brother was a commercial diver in So Cal for about 20 years or so. We were in a shop picking up some regs he was having serviced and while we were waiting, we were watching one of the sales guys talking with a couple that was very new to the sport. On the way out to the car my brother started to laugh. When I asked him what was so funny, he said " for that poor couple in there trying to buy the right gear, would be like you trying to buy a pick up at a monster truck show" I have a feeling he was right.....

 

[jonnythan]

That's a short-term 'instructor convenience' approach, that disregards the points I made earlier about enabling more intuitive grasp of stability, trim and control in the water.

Are we talking about "minimizing an OW course to it's barest essentials in the shortest possible time (for the instructor's benefit)", or are we talking about what is best for the student as a developing diver?

No, we're talking about things that make a traditional BC better than a bpw for basic scuba classes.

Most instructors would have no idea how to properly adjust a bpw anyway.

You seem to think I'm saying that people shouldn't use bpw rigs in OW classes. I'm not.

 

[Them]

Postscript: I went back to the same store and - like last time - asked the first person I saw about BC/. I'm sure I didn't use the same words but the main difference was that I said I was "really new to diving" instead of saying my open water cert dives are this weekend. That may not have mattered a bit.

Before I knew it there were two guys telling me about bc/w gear based on how their own rigs were set up, explaining different approaches, steering me away from prepackaged sets and towards building up exactly what I want from parts, etc. I was seriously impressed. I've been impressed on both visits really.

I know this was dumb and that I ignored some of the best advice on this thread by doing it, but I had made up my mind to do this part-way through this thread (besides, I am one of those screwups who value direct-experience knowledge over money.) I said go. We grabbed a ss backplate, some webbing, various other parts, and two guys, with a bit of help from a third, team-assembled and dry-fitted a system for me from parts. Just the BP/W (i need to do some more research on regulators etc). I will show it to my instructor this weekend but I expect I'll be using the shop's jacket BCD for the cert dives.

If I don't like (or for some reason find I can't get my cert) it I'll take the hit selling it and be glad for the knowledge. I suspect my choice of fluorescent yellow for the harness will cost me a full $10 on the resale value so I hope I like it.

 

[fire_diver]

Just my recommendation, but if that dive shop is letting you use thier gear for training dives, then use it. You will have the rest of your diving days to use the new BP/W. It will also give you a better comparison when you do start to dive the BP.

Yellow harness?1 Just kidding you. You really are a rebel!

 

[Them]

That was my thought on using the shop's BCD. It's free, it's familiar already, and it's what the instructor knows.


Yes, Yellow. Crazy BRIGHT yellow.

Four D rings plus some belt slides, an oxy cheq Mach-V 30lb wing, dive right plate, scubapro tank bands, two xs weight pockets, no-name buckle and i can't remember who made the padded crotch strap. I probably need to figure out more weight/weight holders but it seems like there are some options there and I wanted to see how much weight i was talking about before I added expensive tear away pockets or the like.

 

[fire_diver]

Your backplate setup sounds exactly like mine. After certification, be sure to do a proper weight check in your new gear. If you are using very light, or no wetsuit, then you may not need any weight other than the plate. I would suggest to put the weight pockets on the tanks bands, one left side, one right. But don't be afraid to play with the setup if you feel too head / foot heavy, back heavy, etc.

 

[Them]

I

(Force analysis)



What we've not identified is where we're measuring to ... the mass centroid of the diver-as-a-system is probably right about at the spine at belt height.

...


I was with you until this statement. ...

I suspect the issue is that I am assuming (perhaps incorrectly) that the diver is using the placement of lead weights to adjust the CG relative to CB, most likely at the beginning of the dive. So I wasn't sharing your CG=spine@belt height assumption. I am such a noob that I can't judge "normal" but it seems like the lead is going to be forward (or down for a prone diver) in order to offset the moment of the neg. buoyant tank... And to offset the moment of the forward/down positioned variable displacement buoyancy compensation bladder.

If so, then I agree...but I'll also point out that for that scenario and for an end-of-dive surface float use case, there's not much of a downside to simply adding more air and floating higher out of the water.

Again I must use the scuba inexperience cop-out. I know that back when a typical day for me included an hour playing in the surf the idea of being trapped on the surface by something buoyant would've horrified me. You went into/under waves or you got tumbled and I knew a few people who got seriously hurt in those tumbles. Even buoyant objects like surfboards were pushed down under waves and if you couldn't do that you dropped 'em and were glad of the leash. Of course that's different, I mention it merely to make my bias clear, but to me the surface is a rough place for delicate floating things.

Your backplate setup sounds exactly like mine. After certification, be sure to do a proper weight check in your new gear. If you are using very light, or no wetsuit, then you may not need any weight other than the plate. I would suggest to put the weight pockets on the tanks bands, one left side, one right. But don't be afraid to play with the setup if you feel too head / foot heavy, back heavy, etc.

Cool! That's exactly where the pockets are parked right now.

 

[Crush]

Your wing will let you get away with not using an STA but that will allow your wing to flop about when changing tanks, possibly settling higher or lower between dives. Some book screws like these will prevent that by fixing the wing to the BP.

Buy Highland by XS Scuba Stainless Steel Book Screw, Complete Set from Leisure Pro

BTW, nice purchase.

 

[Them]

Your wing will let you get away with not using an STA but that will allow your wing to flop about when changing tanks, possibly settling higher or lower between dives. Some book screws like these will prevent that by fixing the wing to the BP.

Buy Highland by XS Scuba Stainless Steel Book Screw, Complete Set from Leisure Pro

D'oh. Forgot that in my inventory. There are two "sex bolts" (same thing, but I guess sex sells) holding the wing to the BP.

BTW, nice purchase.

Thanks! I can hardly wait to try it out.

 

[-hh]

(more Force analysis stuff)

I suspect the issue is that I am assuming (perhaps incorrectly) that the diver is using the placement of lead weights to adjust the CG relative to CB, most likely at the beginning of the dive. So I wasn't sharing your CG=spine@belt height assumption. I am such a noob that I can't judge "normal" but it seems like the lead is going to be forward (or down for a prone diver) in order to offset the moment of the neg. buoyant tank... And to offset the moment of the forward/down positioned variable displacement buoyancy compensation bladder.

You're correct that a diver will choose to move lead around based on how he wants to be trimmed out. You can see this partly in the illustrations I provided - - there's some lead weights indicated in red, which change locations slightly in different frames. And what you're running into is the potential for contradiction in requirements between 'trim' elements when horizontal and during a dive, versus the 'trim' when horizontal on a surface float (mostly a post-dive issue more so than pre-): when horizontal, the "put heavy stuff lower" is fine, or even when floating with a full tank, but when one wants to float with an empty+buoyant tank at the end of a dive, you now want those weights to be to the rear...ie, where fire_diver suggested putting weight pockets on the tank bands.

FWIW, I am not at all a fan of weight-integrated BCs, as their front weight pockets are simply not in the right location.

(float height)

Again I must use the scuba inexperience cop-out. I know that back when a typical day for me included an hour playing in the surf the idea of being trapped on the surface by something buoyant would've horrified me. You went into/under waves or you got tumbled and I knew a few people who got seriously hurt in those tumbles. Even buoyant objects like surfboards were pushed down under waves and if you couldn't do that you dropped 'em and were glad of the leash. Of course that's different, I mention it merely to make my bias clear, but to me the surface is a rough place for delicate floating things.

Ah, a surfer! You're right: when you're in the breaking wave zone, there's additional factors that come into play for how a diver will plan to transit the surf zone safety, both coming and going. With the extra weight of all the gear, don't expect to be able to move/react as quickly...or as gracefully.


-hh