Backplate questions for double tank diving

[2airishuman]

If it helps at all, I currently dive a single HP100 with a DSS steel BP (6lb), the weight plates (8lb) and a 10lb weight belt in my drysuit with 400g Thinsulate undies.

You will still want a stainless steel backplate. You cannot use weight plates with doubles. Going from singles to doubles you'll be maybe 5-8 pounds more negative, not including the weight of the gas in the cylinders. Most HP100s are close to neutral when empty although I guess there are some exceptions. I would just start with the backplate you have now. It will probably work just fine.

- Is there a particular shape of backplate that's better for doubles? As in flatter vs deeper? I read that DSS plates are relatively flatter and Halcyon plates have a deeper V. Not sure about any of the other brands (DGX, HOG, Light Monkey, etc).

I don't think it matters much. You want to have room for the nuts, and that's about it.

 

[elgoog]

Here's the math I'm using.

Positive -
Drysuit = +25lb (measured at end of dive with 500psi in tank and with what I consider normal suit inflation .i.e. what I use during the dive)

Negative - (total = -22lb)
Empty tanks = -5lb (galvanized Worthington HP100s, buoyancy with valve is -10lb full, -2.5lb empty)
Steel backplate+harness = -6lb
Doubles regs = -2lb
Manifold = -3lb
Bands = -4lb
Can light = -2lb (the andrewy-brewed Monterey special I have now is nowhere near this but I'm also on the lookout for an HID light and those run in this range)

With the numbers above, I'm not overweighted with a steel plate and don't think there's anything more I would add to the setup that would change that (at least, not that I can think of). It comes down to how much is available for trim adjustments and I agree that there is no way to tell anything about trim until I get in the water and dive. In general, isn't it better to have more weight available to adjust trim? I would think so but I have no firsthand experience with doubles. With a steel plate I would have ~3lb to play with and with AL or Kydex BP, this goes up to ~7lb while still maintaining a balanced rig.

 

[tbone1004]

if you need more than 3-4lbs in a tail weight pouch, then there is something else going on in your setup. Usually crotch strap not tight enough or wrong fins

 

[Ouvea]

elgoogle:

I believe SeaOtter has a set of Faber HP100 that she doubled. I would ask her if she had any difficulty trimming them. You'll find that the amount of weight you carry isn't usually a problem and is determined after a few dives. Now placing the weights to achieve the trim you desire, that's a different story.

In truth, I do not recommend that you buy anything yet. Use the equipment that you have at your disposal and then buy what you need, after you have determined the weight you require and where you're going to locate them. Most of us are head heavy, hence we lengthen our harness to drop the tanks and shift the weight we carry rearward. If you intended on taking the GUE doubles primer course, I would consult with Beto before acquiring any new gear.

The DSS Kydex backplate does have a very flat profile. I do have to flex mine to fasten it to my doubles.

O.

 

[tbone1004]

@Ouvea why do you have to flex yours to get it on your doubles? are the bolts not adjusted properly? My kydex plate goes on my doubles with no flexing at all...

 

[elgoog]

I believe SeaOtter has a set of Faber HP100 that she doubled.

Yep, diving with her in a couple of weeks and she's going to be in the doubles then. Was going to use that time to check her rig out.

In truth, I do not recommend that you buy anything yet. Use the equipment that you have at your disposal and then buy what you need, after you have determined the weight you require and where you're going to locate them.

I'm not in a rush to buy anything, still at the point where I'm trying to see what I should be on the lookout for. Lots of people still left to talk to and their gear to check out before I buy anything.

If you intended on taking the GUE doubles primer course, I would consult with Beto before acquiring any new gear.

Definitely planning on doing this.

 

[Ouvea]

@Ouvea why do you have to flex yours to get it on your doubles? are the bolts not adjusted properly? My kydex plate goes on my doubles with no flexing at all...

It might just be the length of the bolts. In truth, I don't know their length. I just told my LDS to double up my cylinders so I really didn't bother checking actual specs. I let my LDS worry about this. My Kydex plate is very flat and does not have much of a deep center trough.

 

[sea_otter]

I believe SeaOtter has a set of Faber HP100 that she doubled. I would ask her if she had any difficulty trimming them. You'll find that the amount of weight you carry isn't usually a problem and is determined after a few dives. Now placing the weights to achieve the trim you desire, that's a different story.

Close, I have LP85s. I'm able to trim them nicely, but I do have a lot of weight in the tail (v weight cut in half on the bottom bolt only). I'm seriously tempted to switch from the aluminum to a steel backplate, though, as I've now picked up some very warm undies and need more weight to sink them (almost 20 pounds of lead - and don't have great places to put it all). That's the only problem with doubles - the dives get longer and I get colder.

 

[Stoo]

Everyone up here dives doubles with SS plates, except me. I use some ancient old "plastic" thing. I have no idea what brand it is, but it works fine. In my case, I need to drag my tanks into my RHIB after the dive, so having all of the weight in one lump is a pain. One of my more buoyant buds wears steel 100s, with a brass plate, and a V weight. It takes two people fo get them back into the boat.

If I was doing it again however, I would probably get SS just so my friends wouldn't look at me funny.

 

[Jack Hammer]

I own several wings and BPs. What I found over the years that works for me and is good compromise between the perfect size/weight/lift for each dive and keeping it simple is I use an aluminum plate in warmer Waters and a stainless plate in colder Waters. With 7.25" doubles I use a 40#-45# wing and with 8" doubles a 55#-60# wing. I mostly dive steel doubles, however when traveling to tropical waters I use doubled aluminum 80s with a 40#-45# pound wing. That combo carries the weight of all the extra gear and any stages I may have at the beginning of the dive without being overly large and without the need to bring 3 plates and 5 wings for every dive.