Questions concerning Backplates.

[cool_hardware52]

I was on a shallow reef dive last week. I went completely inverted to look under a ledge. Just elevating my wing by that 1 or 2 feet or so caused me to start to rise. Being in fairly shallow water, the ascent accelerated pretty quickly. Attempting to dump air out of the butt dump valve wasn't working to stop my unintended ascent.

Perhaps the specific rotation I went through resulted in most of my air being in the right side of the wing. I don't know. It was warm water, and I was wearing a 3/2 suit, 6 # BP, and 8# of weights, with a 30 pound wing, so there wasn't much air in it, relative to its capacity. Thinking back on it, I think the reef was on my right, so I probably did start horizontal, rotate my right side up, then rotate to feet up/head down. So, it's very possible that most of my wing air was in the right side of the bladder.

Anyway, I ended up having to flip over to a head up position to dump air to stop my ascent. I felt like if I had been diving a donut instead of horseshoe, I could have stopped my ascent without having to flip myself 180 degrees. Or, of course, if I also had a right side dump valve.

16 lbs of total ballast with 3mm suit sounds like a lot to me. 6lbs of plate and harness, 8 lbs of lead and 2 lbs of regulator. Even with a buoyant al80 that's a *lot* of ballast to sink a suit that maybe 3-4 lbs positive. Over weighted leads to more gas in your wing than you need, and that complicates buoyancy control. We routinely see divers using nothing but their SS plate, harness and reg when diving 3mm suits and al 80's

Learning to use the OPV correctly is a skill. To dump *any* gas from the OPV you need to raise the value up to where the gas is in the wing. Pulling *down* on the string instead of pulling *UP* is a sure way to vent nothing. I'd suggest some practice. Try it a little deeper.

The real key to good buoyancy control is planning ahead.

Donut wings are not magic, divers with long experience in BP&W haven't been able to tell the difference between a donut wing and donut wing with a sealed lower arc because gas almost never passes though the lower arc of a donut wing.

It's a well used phrase, but worth understanding; "Don't look for a gear solution to a skills problem"

Good luck,

Tobin

 

[stuartv]

Don't you think it would have been pretty simple to just SWIM downward, that this would be able to push down even 10 or 20 pounds of lift? And I doubt you had much over 5 pounds of lift, unless you went for a full inflation instead of dump

Of course, if you have soft split fins, it is understandable that you could not fight the lift

Yes, I do believe I could have swum (swam?) it down. I was using Atomic Blade fins, I am a decent swimmer (1000 yds in the pool before work 2 or 3 times a week), and I was operating the butt dump so I definitely was not inflating. But, I don't generally think of using my fins to deal with buoyancy issues, so in this case I didn't really try that. I was gently kicking down at first, then I gave up and flipped so I could use the LPI dump.

---------- Post added March 22nd, 2015 at 12:39 AM ----------

16 lbs of total ballast with 3mm suit sounds like a lot to me. 6lbs of plate and harness, 8 lbs of lead and 2 lbs of regulator. Even with a buoyant al80 that's a *lot* of ballast to sink a suit that maybe 3-4 lbs positive. Over weighted leads to more gas in your wing than you need, and that complicates buoyancy control. We routinely see divers using nothing but their SS plate, harness and reg when diving 3mm suits and al 80's

Learning to use the OPV correctly is a skill. To dump *any* gas from the OPV you need to raise the value up to where the gas is in the wing. Pulling *down* on the string instead of pulling *UP* is a sure way to vent nothing. I'd suggest some practice. Try it a little deeper.

The real key to good buoyancy control is planning ahead.

Donut wings are not magic, divers with long experience in BP&W haven't been able to tell the difference between a donut wing and donut wing with a sealed lower arc because gas almost never passes though the lower arc of a donut wing.

It's a well used phrase, but worth understanding; "Don't look for a gear solution to a skills problem"

Good luck,

Tobin

I kind of expected a response like this. And I freely admit that a more skilled diver might not have had the same issue.

But, I also have to say:

I dove the same rig in December with 6 # and had a very hard time holding a SS at the end, so I don't think I'm overweighted. Maybe 1 #.

I believe I am operating the OPV completely correctly. I can feel air dumping out of it (and I understand basic physics).

If you are in horizontal trim, with the wing inflated 25%, and you roll so your right side is up, then you pivot to an inverted position, and then you try to dump a significant portion of the air in your wing, while staying (substantially) inverted, are you really saying that a donut versus a horseshoe won't make any difference?

Lastly, I don't buy into the "don't look for a gear solution to a skills problem" concept. I have been and will continue to work on improving my skills. But, at the same time, if a different piece of gear will give me better performance, I'm interested! I will still continue to work on improving my skills. If I were more skilled, I might be able to dive with less ballast. Does that mean, I should go with less weight and not be able to hold a SS? If I were more skilled, I might be able to have the same SAC using cheaper fins. Does that mean I should have bought the cheaper fins and suffered with the reduced bottom time until my skills improved? If I were more skilled, I could probably maintain good buoyancy control and trim even with a jacket style BC. Does that mean I should have bought a cheap one of those instead of my DSS BPW?

 

[Scared Silly]

Getting the thread back on topic. The one feature that has been mentioned only once that I think bares repeating is the ability to use the backplate with a single tank sans adaptor. Backplates came from the technical side and double tanks. WHen diving a single cylinder one needed an adaptor. However, today with so people diving BP with single many plates like the DSS are built that way. Some like the Freedom plate are singles only. That is a good feature - especially when traveling as it is one less thing and weight to deal with.

 

[Rooster59]

Hey Tobin,

My brain hurts too much to understand this- "To dump *any* gas from the OPV you need to raise the valve up to where the gas is in the wing. Pulling *down* on the string instead of pulling *UP* is a sure way to vent nothing."

I get where the gas has to be at the valve, but can you re-explain the pulling *down* and *UP* part?.

Thanks!

 

[cool_hardware52]

Yes, I do believe I could have swum (swam?) it down. I was using Atomic Blade fins, I am a decent swimmer (1000 yds in the pool before work 2 or 3 times a week), and I was operating the butt dump so I definitely was not inflating. But, I don't generally think of using my fins to deal with buoyancy issues, so in this case I didn't really try that. I was gently kicking down at first, then I gave up and flipped so I could use the LPI dump.

---------- Post added March 22nd, 2015 at 12:39 AM ----------



I kind of expected a response like this. And I freely admit that a more skilled diver might not have had the same issue.

But, I also have to say:

I dove the same rig in December with 6 # and had a very hard time holding a SS at the end, so I don't think I'm overweighted. Maybe 1 #.

I believe I am operating the OPV completely correctly. I can feel air dumping out of it (and I understand basic physics).

If you are in horizontal trim, with the wing inflated 25%, and you roll so your right side is up, then you pivot to an inverted position, and then you try to dump a significant portion of the air in your wing, while staying (substantially) inverted, are you really saying that a donut versus a horseshoe won't make any difference?

Lastly, I don't buy into the "don't look for a gear solution to a skills problem" concept. I have been and will continue to work on improving my skills. But, at the same time, if a different piece of gear will give me better performance, I'm interested! I will still continue to work on improving my skills. If I were more skilled, I might be able to dive with less ballast. Does that mean, I should go with less weight and not be able to hold a SS? If I were more skilled, I might be able to have the same SAC using cheaper fins. Does that mean I should have bought the cheaper fins and suffered with the reduced bottom time until my skills improved? If I were more skilled, I could probably maintain good buoyancy control and trim even with a jacket style BC. Does that mean I should have bought a cheap one of those instead of my DSS BPW?

You have reported that a 1 ft change in depth at 30 ft started a nearly uncontrollable ascent because you could not dump sufficient gas from only the left side of your wing. The amount gas one needs to dump for a 1 ft change at 30 ft in 3mm suit is tiny, most divers can do that with their lungs.

How did you manage using the "flawed" design of a horseshoe wing to shift 100% of the gas in your wing to the right side just prior to your near corking leaving not even a puff of gas in the left side? I doubt I could do that if I wanted too……...

Your suit is *maybe* +4 lbs. and if you were using al 80 it would be +4 dead empty. I still don't see where you need 16 lbs of ballast. That suggests you are 8lbs personally buoyant. That would be extremely odd. One of the real joys of thin suits, modest gas volumes and proper weighting is the ability to do long shallow reef dives with almost no gas in your wing, using only your lungs for most depth changes.

You are a new diver, all I can do is again repeat that looking for a gear based solution vs skills is expensive and ultimately fruitless.



Tobin

---------- Post added March 22nd, 2015 at 08:25 AM ----------

Hey Tobin,

My brain hurts too much to understand this- "To dump *any* gas from the OPV you need to raise the valve up to where the gas is in the wing. Pulling *down* on the string instead of pulling *UP* is a sure way to vent nothing."

I get where the gas has to be at the valve, but can you re-explain the pulling *down* and *UP* part?.

Thanks!

Rooster,

Picture a horizontally trimmed diver with a partially inflated wing. The gas is in a bubble running down each side of his wing and along side the cylinder. The OPV is located on the divers side of the wing. At first glance that looks like the "wrong" side for the valve if you want to dump gas in trim. In reality the wing will wrap the tank slightly and now the OPV is not on the underside of the wing, but is on the "outside" of the wing near the top of the wrapped wing. If a diver reaches back and grabs the pull cord and pulls "down" i.e. toward the bottom of the ocean the corner of the wing will be pulled down too and the gas that was in that corner will go somewhere else in the wing. OTOH is the diver pulls the string Up towards the surface the opv and wing is lifted, and the gas in the wing is able to escape as intended.


All too often divers moving from a jacket BC are used to having 1/2 dozen dumps, many operated by cords routed all over the BC and a cable actuated quick dump on the inflator (pull dump instead of plain elbow) at the hose connection of the BC. These divers are accustomed to simply yank on this or that cord or hose until gas is dumped with no concern for where the gas is in the BC. This is the key difference when moving to a simple BP&W.


Hope this helps.

Tobin

 

[Rooster59]

OK, crystal clear now.

I always reach down and grab like this, and pull my fingers apart to activate the valve, that part of the wing itself doesn't move. I never even thought about it, I just roll my hip up a bit then pull.

Thanks!

 

[Eric Sedletzky]

OK, crystal clear now.

I always reach down and grab like this, and pull my fingers apart to activate the valve, that part of the wing itself doesn't move. I never even thought about it, I just roll my hip up a bit then pull.

Thanks!


View attachment 205179

OMG!!! you still have the plastic knob on the end???
Don't you know that's totally non DIR compliant and you'll die!

 

[cool_hardware52]

OMG!!! you still have the plastic knob on the end???
Don't you know that's totally non DIR compliant and you'll die!

While the knob of toggle is not likely to be a great risk for single tank recreational divers there are good reasons for not using the "toggle" on a wing OPV. It's easy to get it tangled on a left hip dring, particularly when you have bottles clipped off there. It's also easy to get a toggle stuck between to stage / deco bottles. The wider profile of doubles wings puts the OPV and hip dring in close proximity for many divers. Less so for single tanks, but it can still happen.


The common modification is to remove the toggle and replace the cord with a thicker cord (typically 3mm) that is a bit longer and has a few knots in it. That works great for Pulling but.....

The recess in the inner valve seat retainer is too small to allow for a proper knot on 3mm cord. People end up melting a "blob" on the end of the cord and these can break off.

That's why DSS builds their own OPV's

Once you make the recess in the inner valve seat retainer large enough / tall enough for a proper knot the standard OPV outer cage is no longer tall enough for the valve to open, the taller seat retainer hits the underside of the cage.

This requires a new outer cage.

Seems like a minor issue, but fixing it requires two custom injection molds.

Tobin

 

[cool_hardware52]

Here's a pic of the DSS valve Seat Retainer (left side) with a larger deeper recess and the industry standard Valve Seat retainer (Right side)



Here's a pic showing a knoted 3mm cord can't fit in the industry standard Valve Seat Retainer



And a pic showing the 3mm cord with knot in the DSS Valve Seat Retainer

 

[stuartv]

You have reported that a 1 ft change in depth at 30 ft started a nearly uncontrollable ascent

No, I didn't. I said 1 to 2 feet and the depth I stated was "shallow". I will clarify that the depth was closer to 15'.

Also, you did not answer this question :

If you are in horizontal trim, with the wing inflated 25%, and you roll so your right side is up, then you pivot to an inverted position, and then you try to dump a significant portion of the air in your wing, while staying (substantially) inverted, are you really saying that a donut versus a horseshoe won't make any difference?

And if it doesn't make any difference then what is the reason for offering a donut? What IS the reason to choose a donut over a horseshoe?