Backplate bend revisited

[*Floater*]

As I understand it, less bend in a backplate puts the tank closer to the back thus increasing stability when diving single tanks. More bend allows single tank wings with narrow center panels to inflate more fully and creates more space for liftbag or SMB storage using a backplate pad. Are there other advantages or disadvantages?

Also, for those of who have used plates with different degrees of bend please post how they felt different, if at all, for diving singles and doubles?

And if you have a chance please measure and post the amount of bend in the plate/s you own. I'd like to know the differences.

As for me, I've only used DSS plates and they've felt fine with both singles and doubles, but then I don't have anything to compare them to. I traced the (inside) outline of one of my DSS plates and measured it with a protractor. The result I got was 13 degrees of bend.

 

[GreenDiverDown]

I have FredT plates, Halcyon plates, DSS plates, and OMS plates. In the water they feel the same to me. I choose my plate for a particular dive by its weight and not by its bend angles.

 

[The Kraken]

On my single plate I employ a 45 degree bend coming off the raised rib and a 5 degree bend where you show 13 degrees. The rib isn't as nearly as high as it is for a doubles plate.

On the double plate I incorporate approximately a 20 degree bend where you show 13 degrees.

the K

 

[cool_hardware52]

More bend allows single tank wings with narrow center panels to inflate more fully

Only at the expense of a higher profile tank position, i.e. the tank further from the diver. In normal use wings are seldom fully inflated, and then typically only at the surface.

and creates more space for liftbag or SMB storage using a backplate pad.

This I agree with, low profile plates provide less room between the diver and the plate for storage. There are alternative locations and means of carrying inflatables.

Are there other advantages or disadvantages?

There are a number, but I'll keep quite for now. I'm curious what others percieve.

Tobin

 

[*Floater*]

On my single plate I employ a 45 degree bend coming off the raised rib and a 5 degree bend where you show 13 degrees. The rib isn't as nearly as high as it is for a doubles plate.

On the double plate I incorporate approximately a 20 degree bend where you show 13 degrees.

the K

Hey K, could you elaborate on why you chose ~20 degrees of bend for your doubles plate? I assume it's not just for liftbag storage space...

 

[Mr.X]

Much like Stephen I use a variety of plates. Fred T, OMS, Halcyon, Dive Rite, Hammerhead, Abyss and Deep Outdoors. Different plates for different jobs + lead off-setting weight. The geometry of the harness slots can be a factor though. One out of the bunch was immediately sold off. I also find they dive the same. I do like Hammerhead and Fred T's hole options. IMO the most comfortable bend is Halcyon's minimal bend.

Stuffing - the issue becomes whether the plate has enough holes to accommodate the sack and other clip-on items. I can cram pretty much anything in there. Some sacks are better than others. OMS's backplate sack is only so-so. Halcyon being the best of the bunch.

I dive a rebreather & the plate with the flattest profile works best. Some fellas took an heavy mallet to their OMS plates to flatten them out. Of course, plates like this are totally useless for OC doubles config.

X

 

[Doc Intrepid]

I own 3 different "bends": a FredT, a Halcyon, and one of Scott Koplin's early plates. Of the three, Fred's and the H are pretty close, although there may be a few degrees of variance. Scott's is significantly flatter. One of the issues with Scott's is that the flatter bend pulls the center of the plate further away from the bolts on a set of doubles. The result is that the bolts on my four sets of doubles fit Fred's and the H plate, but are too short with Scott's plate when you add the wing. Scott's plate is currently set up for singles only (with a STA), and I sometimes use it when moving sets of doubles to and from the van - e.g. just the plate and the doubles, no wing.

OTOH, the flatter plate brings the tank valve on a single tank closer to the back of the diver's head - so the tank valve can more easily be manipulated. This would be a pretty significant benefit of a flatter plate when diving singles with bp/w (especially when using a STA).

FWIW... YMMV.

Doc

 

[cool_hardware52]

One of the issues with Scott's is that the flatter bend pulls the center of the plate further away from the bolts on a set of doubles. The result is that the bolts on my four sets of doubles fit Fred's and the H plate, but are too short with Scott's plate when you add the wing.

Just to clarify. A steeply bent plate allows the use of shorter band bolts on doubles, than would be required on a flatter plate. This is readily apparent to most.

What is not well understood is the relationship between bolt lenght and clearance to the divers back or exposure suit.

For the same set of doubles, using the same set of band bolts, changing from a steeply bent plate to a flatter plate will not change the distance from the bolt tip to the divers back. (This of course assumes the bolts are long enough to be used with either plate)

Double tanks are usually about 8.5" apart, center to center. That's also about how wide most backplates are. That means double tanks contact the backplate right down the outside edge, from top to bottom. Back plates, even fairly flat backplates, contact the divers back down the outside edges or close to it. (the exception would be dead flat plates, i.e. zero bend)

This means for all pratical purposes double tanks are seperated from the divers back by the thickness of the backplate (and fabric of the wing) If the tanks are contacting the divers back, swapping between steep plates and flatter plates won't move the bolts in relation to the divers back.

If your band bolts are set up as per these recommendations you should be able to use steeply bent or flatter plates
http://www.diveriteexpress.com/library/doubles.shtml

If your bolts are cut short you may be only able to use steeply bent plates, or plates with deep center channels.

Our Delrin Thumbwheels require only ~ 5/16" of band bolt to protrude through the plate to make a secure connection. There is no need to use excessively long band bolts.


Tobin

 

[*Floater*]

On my single plate I employ a 45 degree bend coming off the raised rib and a 5 degree bend where you show 13 degrees. The rib isn't as nearly as high as it is for a doubles plate.

On the double plate I incorporate approximately a 20 degree bend where you show 13 degrees.

the K

Just to quantify the effect of the bend on the closeness of the tank I did a quick calculation, and for an average plate (say 10.5" wide) the 5 degree bend would bring the tank a third of an inch closer relative to the 13 degree bend, all else equal, while the 20 degree bend would take the tank about a third of an inch further. Or more generally, each +/- 7 degrees results in roughly +/- 1/3 inches.

edit: Using the 8.5" for plate width (top of plate), the difference would be about 1/4 of an inch per 7 degrees of bend, all else equal. That's probably more realistic.

 

[cool_hardware52]

Just to quantify the effect of the bend on the closeness of the tank I did a quick calculation, and for an average plate (say 10.5" wide) the 5 degree bend would bring the tank a third of an inch closer relative to the 13 degree bend, all else equal, while the 20 degree bend would take the tank about a third of an inch further. Or more generally, each +/- 7 degrees results in roughly +/- 1/3 inches.

edit: Using the 8.5" for plate width (top of plate), the difference would be about 1/4 of an inch per 7 degrees of bend, all else equal. That's probably more realistic.

Overall plate bend is only one factor, the depth of the center channel is independent of the overall plate bend. Center channel depth, and width varies widely.


Tobin