Single 100 W/ 18 Pony On Bp/w

[Steelyeyes]

I dive a Whites Bullet dry suit in Puget Sound. My tank is an HP 100 and I dive with total weight load of 32ish pounds. Some weight is in my BCD in ditchable pockets, some in the trim pockets near the tank, 12 lb. is on a soft weight belt, and I have 3 lb. total in ankle weights.

I'm going to get an 18 cubic foot pony rig and plan on mounting it to my main tank in a valve down configuration. My current BCD is a bit undersized since I bought it for warm water diving years ago.

I'm interested in buying a backplate and wing set up with a bit more lift. I was thinking 40 lb (current BCD is 35 lb. of lift). I'm not brand conscious so whatever works the best is what I'll get and I'm not overly worried about price.

There are two things I'm in a quandary about.

One is that the inner bag/outer skin arrangement on the suit makes air migration in the suit a little problematic and I don't think wearing a BCD with a cumerbund and a 12 lb. weight belt is helping that situation. In a horizontal position over time air moves to my legs as it should but when I ascend it takes longer than I like to move back up to the vent when I'm trying to get rid of it. That leaves me with positive buoyancy I don't want. I think going to a more simple harness and moving all of my weight (besides my ankle weights) to the harness and wing will help solve that problem.

The second thing is the tank mount. If I get a setup with a backplate for a single tank and put a pony on the side will that leave the wing enough room to properly inflate or should I go with a STA to move the tank and the pony away from my back to give it more room to expand and not get pinched? The shops around here don't have a lot of examples on the floor to look at and those that do generally carry one brand so hands on investigation burns a lot of gas.

Thanks for any suggestions.

 

[halocline]

I would think about slinging the pony bottle. Actually I'd probably suggest forgetting about the pony, and if you are diving in a situation where you really need redundancy beyond your buddy, consider some technical training and true redundancy, i.e. doubles. Small ponies are IMO (many people will disagree with this) not much more than 'feel good' devices that likely do not provide an appreciable safety factor. But there are no real studies so it's all conjecture.

Anyhow, if you are really set on the pony, sling it. You'll have way more control over it, it will solve your wing issue, and it will help train you if you move into using full size bottles like stages for technical diving.

You'll love going to a BP/W with the hogarthian harness. You might give Tobin a call at deep sea supply; he'll offer expert advice about your set up.

 

[tbone1004]

deep sea supply stainless plate, quite possibly with the weight plates, and a LCD40 wing will be just dandy. I'd agree on slinging, though the 18 might be a bit awkward, I prefer to go with something much larger for ponies with an al30 or al40 being the preferred. Do the rock bottom calculation at the depths you are diving, an al18 at 100ft doesn't give you any buffer...

 

[decompression]

What Tbone said......

 

[eelnoraa]

Pony is for the diver him/herself, the normal rock bottom calculation probably don't apply here. so 18cf should be enough for 100ft bottom. Thought I also prefer sling al40. It is a lot more versatile piece of equipment.

Having that said, I think 35lb should be more than hp100+pony eve al40. Keep in mind, lift is a function of your suit, which didn't change. And function of the gas you are carrying, not the tank. 140cf of nitrox is only 11lb. 35lb lift is plenty.

 

[tbone1004]

I run rock bottom calculations with 1cfm combined. 1cfm for diver 1 and 0 for diver 2. Based on the online calculator it's 20cf required. Will it get you up? Certainly, but why run the risk with no safety buffer?

 

[Steelyeyes]

After more reading I'm leaning more toward a 30 cu. tank because it would provide a better margin of safety. Mounting it on back then would be more weight to lug around topside so slinging it would make more sense.

I'll see about borrowing or renting something to test the idea out on to see if I like diving like that. I'm planning on doing more training although I think I'll try and get that somewhere warmer unless I really fall in love with the wrecks up in BC. Thanks for the input.

 

[2airishuman]

As is pointed out frequently here I don't know anything about anything so please disregard anything I put here and consult the Gods of Cave Diving for a more Authoritative Answer if that's what you want.

Nonetheless I dive with a BP/W and a pony and feel I may be able to share such insight as I may possess.

I'm going to get an 18 cubic foot pony rig and plan on mounting it to my main tank in a valve down configuration. My current BCD is a bit undersized since I bought it for warm water diving years ago.

18 cf is an odd size. Perhaps you have an AL19 in mind, unless you are planning to dive an unusual older LP steel pony. One thing to consider with odd size ponies in a backmount configuration is that many of the mounting systems only work with certain specific cylinder diameters, so be sure everything you intend to use is compatible.

I see you're considering a slung AL30 also. I have been carrying a slung AL19.

I have run a variety of gas management calculations in a variety of scenarios and have concluded that an AL19 is sufficient for the depths and situations where I plan to dive with it, generally at depths less than 50 feet. An advantage of a slung cylinder is that it is easy enough to switch to a larger one for any particular dives that warrant it.

The larger and heavier the pony cylinder, the less likely you are to bring it along on all dives.

The second thing is the tank mount. If I get a setup with a backplate for a single tank and put a pony on the side will that leave the wing enough room to properly inflate or should I go with a STA to move the tank and the pony away from my back to give it more room to expand and not get pinched? The shops around here don't have a lot of examples on the floor to look at and those that do generally carry one brand so hands on investigation burns a lot of gas.

There are a wide variety of pony mounts out there for back mount use. In general they allow you to mount the tank at any angle to the primary tank that you need in order to get enough clearance. You do have to leave room for the cam band buckles to close but in general clearance isn't a problem from what I've seen.

 

[2airishuman]

I would think about slinging the pony bottle.

This is good advice but let's go over the reasons.
- You will be able to reach the cylinder valve on the pony and therefore have the option of carrying it with the valve off.
- You can easily see an SPG for the pony, either button style or on a hose.
- You are less likely to mix up regulators because the pony regulator is bolt-snapped or bungeed to the pony tank making its purpose clear. Also, if you carry valve off, that will also help prevent wrong-reg accidents.
- You can unclip the pony and abandon your kit in the rare situations that require it.
- Costs are low and there are no pony-specific components that remain attached to the tank or BC.
- You can switch pony sizes to fit the dive.
- As Halocline noted upthread, a slung pony helps develop skills useful for carrying stage or deco gases, should that be a direction your diving may take you.

Actually I'd probably suggest forgetting about the pony, and if you are diving in a situation where you really need redundancy beyond your buddy, consider some technical training and true redundancy, i.e. doubles. Small ponies are IMO (many people will disagree with this) not much more than 'feel good' devices that likely do not provide an appreciable safety factor. But there are no real studies so it's all conjecture.

While I think there is wisdom in this, there are many dives where doubles aren't feasible but a pony is.

You'll love going to a BP/W with the hogarthian harness. You might give Tobin a call at deep sea supply; he'll offer expert advice about your set up.

I have a DSS backplate and wing, and I like it. The DSS BP/W has a uniquely well thought out system for single tanks that doesn't require an adapter or rethreading the cam bands whenever the wing is removed.