which backplate

[cool_hardware52]

Honestly, the plate's profile is too flat. It places the isolator too close to my head. With a single this is great. You can reach the knob easier. But with doubles, the isolator is RIGHT behind your head, and I like to rest my head on it when I swim. It reminds me to arch my back.

Again, this is just a personal thing, and others may disagree.

Perrone,

The overall bend, and depth of the center channel does effect the position of a single tank relative to the diver's back, but has alomost no effect on the position of doubles.

Consider this; When wearing doubles the tanks contact the back plate close the edge of the back plate. This is also where the back plate contacts the divers back, near the right and left edge of the plate. This means that the tanks are effectively spaced from the divers back by the thickness of the plate.

Don't have to believe me, just mock up a set. The center of your back, where your spine is, does not touch the plate at all. A typical manifold is 215 mm ( ~8.5 inches) center to center. Back plates taper from about 9 inches at the top to about 10.5-11 inches wide near the bottom. If plates average about 10 inches wide, and Doubles are ~8.5" wide where they contact the plate how can plate bend effect the spacing of the tanks from the divers back?

This is true regardless of either the overall bend of the backplate, or the depth of the center channel.

7" (or 7.25") tanks will place the iso closer to the diver than when using 8" tanks. Different manifolds, or more specifically different valve knobs will provide more or less clearance for your head. Angling the iso straight up, or even away from the diver can provide more clearance.

Regards,


Tobin

 

[cool_hardware52]

Hello Mikhail,

Deep Sea Supply uses 300 series stainless steel in their backplates, which has a slightly higher carbon content I believe. Tobin of Deep Sea Supply states that if a piece of stainless is correctly passivated (treated so that a thin layer of oxide is present on the metal surface), it will resist corrosion very well.

Passivation removes free iron that can act as the starting point for corrosion. Free iron can be imparted from the tools used to cut and shape stainless.

Tell me what's more likely, corrosion on unpassivated 316 or on passivated 304? The cutting and bending tools used on 316 will easily impart small particles of iron.

I believe the major reason many manufacturers use 300 series stainless steel is because it is cheaper than 316 and is just as functional.

That's true, 304 is a little cheaper than 316, but passivation is an additional process, and is not done for free.

When would I select 316 over 304? If I had an application where stainless is exposed for extended periods to highly corrosive environments at elevated temperatures. Scuba divers generally avoid boiling tanks of corrosive sauce. Scuba divers can rinse their gear too, unlike say a pipe in a paper pulp mill.

BTW, the "L" or low carbon variety of either 304 or 316 would be selected for improved weldability.

Deep Sea Supply uses plastic inserts around the slots which prevents any damage to the webbing, a very nice feature.

The elastomeric grommets in the corners of our plates are not "inserted" but are in fact molded on to the plate. The backplates are placed in an injection molding machine and the TPU is injected through the plate. These grommets not only provide a cushioned edge for the webbing they increase the effective thickness of the plate from ~.118" to almost 1/4" thick. This increased beaing area cannot be achieved by radiusing a .118" thick plate.

Regards,


Tobin

 

[LG Diver]

I've not had the opportunity to dive one of Tobin's plates, but I've seen them and they are very nicely made.
I have a FredT heavy plate (9 lb) and STA (5 lb) and am extremely happy with it. I don't think you can really go wrong with the DSS or FredT plates. I'd pick either of these over a Halcyon plate in a heartbeat. If you're diving cold water the heavy FredT plate or the DSS plate with weight plates are a significant advantage. I can't speak to the Hammerhead plate, as I've never seen one in person.

 

[Sadamune]

Hi Tobin,

Thanks for the clarification on your elastomeric grommets. It is the best solution to the sharp edge problem that I've seen.

As for the passivation issue, it is my understanding that any material that spontaneously forms a hard, non-reactive surface film in the presence of oxygen is conferred corrosion resistance. Thus, all stainless steels becomes passivated when exposed to regular air. However, you seem to refer to a different passivation process. Do your backplates undergo a more specialised form of passivation? Perhaps pickling?

Another question, if a 300 series backplate is left in the sun after a salt water dive, wouldn't the areas where salt water collects, e.g. under grommets, washers, etc., be susceptible to pit corrosion (chloride ions competing with oxygen on a hot substrate)?

From what I've read, the "L" does relate to welding, referring to grades with .03% or less carbon, which helps prevent carbide precipitation during welding that can promote corrosion. I wonder if FredT has a specific reason for using it...

Cheers,

Sadamune

 

[MaxBottomtime]

Another one is the Freedom plate. It curves around your hips and holds a tank closer than flat plates.
http://www.pacificcoastmarine.net/freedom plate.htm

 

[cool_hardware52]

Hi Tobin,


As for the passivation issue, it is my understanding that any material that spontaneously forms a hard, non-reactive surface film in the presence of oxygen is conferred corrosion resistance. Thus, all stainless steels becomes passivated when exposed to regular air. However, you seem to refer to a different passivation process. Do your backplates undergo a more specialised form of passivation? Perhaps pickling?

Passivation is specifically the removal of free iron from the surface. Stainless does not spontaneously passivate. Passivation can be achieved a variety of ways. Heated nitric acid, or electropolishing are two common approches. It is the removal of the free iron that allows a continuous oxide layer to form spontaneously.

Another concern, if a 300 series backplate is left in the sun after a salt water dive, wouldn't the areas where salt water collects, e.g. under grommets, washers, etc., be susceptible to pit corrosion (chloride ions competing with oxygen ions on a hot substrate)?

If you rinse your gear on a simi regular basis it's just not an issue worth worrying about. Given that the vast majority of ss Backplates in current use are 304, not 316, either minor discoloration is accepted, or routine gear maintainance is sufficient.

From what I've read, the "L" does relate to welding, referring to grades with .03% or less carbon, which helps prevent carbon precipitation during welding that can promote corrosion. I wonder if FredT has a specific reason for using it...

If I wanted to skip the passivation 316 might be worth considering. I prefer to have 304 without free iron to 316 that might still have free iron. It's a manufacturing choice, spend more on 316 and skip passivation, or buy slightly cheaper 304 and pay to passivate it.


Tobin

 

[SangP]

Mikhail Frenkel,

There are many options on a plate but I'll just add a bit more to what has been said already in that price wise a Hammerhead ss plate and sta is hard to beat. But in terms of designs that I like I would prefer to get a Oxycheq, Gary Hoadley. I prefer plates that have angled shoulder slots instead of flat slots as in Halcyon, OMS, Fred T as it feels more comfortable.

I would say since this is your first plate the Hammerhead is a great choice as it is really resonable, has the most number of mounting holes (not that you need that many anyway), is right in the middle of the road in terms of height profile, and bends that is equally comfortable for both double and singles heck for $100 you even get an STA.

SangP

 

[TSandM]

It may well be that all plates and wings are compatible if you use an STA. But I have had the experience of trying to put one of DSS's lovely torus wings on another manufacturer's plate. The DSS singles wing has a built-in STA, but the center window of the wing where the cambands come through is too narrow for the other make of plate. Failing to recognize the range of issues caused by this led to a somewhat exciting dive involving the replacement of my tank at 100 fsw.

 

[SangP]

TSandM,

Good point... Mikhail Frenkel, when you get a wing, make sure it fits your wing with or without an sta just in case.

SangP

 

[bradshsi]

Another question, if a 300 series backplate is left in the sun after a salt water dive, wouldn't the areas where salt water collects, e.g. under grommets, washers, etc., be susceptible to pit corrosion (chloride ions competing with oxygen on a hot substrate)?

From what I've read, the "L" does relate to welding, referring to grades with .03% or less carbon, which helps prevent carbide precipitation during welding that can promote corrosion. I wonder if FredT has a specific reason for using it...

Cheers,

Sadamune

If your really worried about crevice corrosion in 300 series steels (and like leaving your gear unrinsed), you could always try and talk Tobin into making you a backplate from Duplex stainless steel. Somehow though I suspect the premium price tag might be sufficient incentive to buy a 304 backplate and rinse it

Since the backplate isn't welded, using an L grade of stainless is going to have no practical impact on the corrosion resistance. Intergranular corrosion is specific to location where welds have been made. However L grades tend to be a little softer and easier to work. Perhaps Fred T uses it for that reason.