Weighting Going From Single To Double Steels

[wetb4igetinthewater]

Going from single tank with 117 cu ft steel with 19 cu ft pony, 6 lb plate, I had 23 extra lbs. With double 110 cu ft steel, 6 lb plate, I have about 20. But I'm still fine tuning it.

 

[cool_hardware52]

I was bored at some point and weighted a lot of dive gears. Here is what I can share. Photos can be post upon request:
1. brass din first stage, MK25 and Atomic M1 in this case, ~1.35lb.
2. Thermo single pro valve: 1.5lb each
3. Thermo 230bar manifold: 4.9b total. => Cross bar along is 1.9lb only
4. Highland 2.5" wide, 7.25" diameter band set: 3.9lb
5. Most stainless steel plate quoted for 6lb is actually just above 5lb. DR SS plate: 5.06lb.

So adding a x-7 HP100, that is -2lb. Adding a 1st stage: -1.35lb. Added cross bar: -1.9lb. Adding bands: -3.9lb. Total is just a bit over 8lb. Assuming you are not changing your plate, you can subtract 8lb from your weight belt. It is inline with my own experience.

Most "Medium" or "Standard" SS plates are right around 5 lbs, the harness however, adds ~ 1 lbs too. Particularly if a quality heavy gauge waist buckle is used. I quote 6 lbs for a SS plate and harness.

Modular tank valves tend to be heavier than conventional single tank valves. A pair of modulars + an Iso Bar adds 3-4 lbs more than a pair of non modular valves.

Tobin

 

[cool_hardware52]

All,
Just trying to get a rough idea of what to expect going from single steel to double (yes I know the whole story of doing a weight check...etc. just looking for a place to start). Currently in fresh water cold diving with drysuit I wear 15lbs lead, steel backplate (6lbs) with steel cambands(not plastic...add probably 1lb negative), and a STA (2lbs) along with a Faber FX 100 (which is about -.5lbs empty). I will be going to double tank Worthington x7-100 which are a bit more negative compared to the Faber FX100s. How negative are a typical manifold and tank bands? I know I will add another reg set so that may be another say 2-4lbs negative as well. Any thoughts and considerations to get me a ballpark. I will be doing the proper weight check when I get to the water, just want an idea of where I might end up. Thanks!

The goal with doubles remains the same as singles i.e. being able to hold a shallow stop with near empty tanks. What changes a bit are the assumptions. With singles you need everything you have with you that doesn't float to equal the buoyancy of your suit at your last stop, typically 15 ft. A 3 minute safety stop when no stop single tank diving can be tolerated in a pretty tight suit on that day your gas plan leaves a bit to be desired and you arrive at your safety stop with minimum gas.

With doubles that's a bad idea. Doubles implies staged deco, and if you lose access to some or all of your deco gases and you have to deco on back gas your shallow stop times can get quite long. You don't want to be trying to stretch your back gas while shivering in a shrink wrapped suit. Being cold sucks and being cold interferes with off gassing. That means you need to have enough ballast to allow you to add gas to your suit at your shallow stop.

To be able to hold a shallow stop with near empty back gas tanks and a fluffed up suit requires you to start the dive negative by the weight of your back gas +2-3 additional lbs.

Calculating this number starts with knowing how positive your suit is with minimum gas in it. Once you know that number the rest is straight forward, just add up the known weights of the components in your rig. eelnoraa's list will get you fairly close.

To test your suit:

Put on your undies and suit (the actual undies you are going to dive)
Jump into neck deep water holding a bag of "too much" lead
Vent the suit
Pick up your feet. If you sink remove some lead from the bag.
Repeat until you just barely sink
Weigh the bag of lead.

Tobin

 

[eelnoraa]

Most "Medium" or "Standard" SS plates are right around 5 lbs, the harness however, adds ~ 1 lbs too. Particularly if a quality heavy gauge waist buckle is used. I quote 6 lbs for a SS plate and harness.

Modular tank valves tend to be heavier than conventional single tank valves. A pair of modulars + an Iso Bar adds 3-4 lbs more than a pair of non modular valves.

Tobin

I have more weight numbers:
- H small plate by itself is 4lb-1.9lz (or ~4.1lb)
- Same plate with full DIR style harness, including crotch strap, knife sheav, but not knife is 6lb-0.3oz. => the full harness is 1lb-14.4oz (~1.9lb). That is with 2 stainless steel buckle, 5-ring harness, 2 2-ring crotch strap.

And in my measurement, these are exactly the number.
- Thermo single pro valve: 1.5lb each
- Thermo 230bar manifold: 4.9b total.
so 2 single tank value is 3lb total. A full manifold (two modular + cross bar) is 4.9lb. So ~2lb differences

 

[Storker]

Doubles implies staged deco

Maybe in your part of the world, but definitely not in my part of the world. As a rough estimate, I'd guess that perhaps 30-40% of my active clubmates use rec doubles, and the most common type is probably the D8.5Lx232bar. That's far from enough gas for a deco dive, but an nice amount for a cold water rec dive in a DS. For deco diving, I'd say that the most common twinset around here probably is a D12Lx232bar.

 

[Storker]

Now to the topic of the thread: Bouyancy change due to changing or adding tanks can be rather accurately - and easily - calculated, especially with metric tank designations. Let's say I switch from a single Faber 12Lx232bar to a Eurocylinder D8.5Lx232bar:

The gross buoyancy of the tank is given by its external volume. A 12x232 has an internal water volume of 12L. The volume of the walls is the weight of the tank (stamped on the tank's shoulder; a Faber 12x232 is 14.1kg) divided by the density of steel, so 14.1kg / 7.8 kg/dm3 = 1.8L. Total volume of the tank is 12+1.8=13.8L, the empty tank weighs 14.1kg, so it's 0.3kg negative. When empty, and not including the valve and the 1st stage.

A 8.5L Eurocylinder weighs 10.4kg. So, its external volume is 8.5 + 10.4/7.8 = 9.8L. IOW, it's a little less than 0.6kg negative. Times two, that's 1.1kg.

So, by going from a single 12x232 to a D8.5, the buoyancy difference of the two tanksets is just a smidgen less than a kg. Add the bands, the manifold, the second valve and the second 1st (which eelnoraa has weighed for us), and I can subtract an additonal 5kg from my belt. In total, I'll need about 6kg less with the twinset.

Since I've used several different types of steel singles, I've done this type of calculation a few times. I've always ended with an estimate within about one kilo from what I've ended up with after the buoyancy check. That's good enough for me.

 

[sheeper]

DiveRite Transplate single with steel STA and steel plate and Faber HP100 steel tank, 3mm wetsuit - Zero lead
Same as about with Drysuit - 16 pounds lead
Steel Doubles, DiveRite Transplate double wing with drysuit - zero lead

i found that calculations i made were always off. so i went to trial and error method to dial in exact weighting. Always carry an alternate lift method with doubles. Either a dual bladder or a lift bag

 

[cool_hardware52]

Maybe in your part of the world, but definitely not in my part of the world.

Er, ah, well, if you read the OP you will see he is 1) in New York and 2) planning on 2 x 100 cu ft tanks. I've done many, many deco dives on lp 85's or HP100's.

Tobin

 

[cool_hardware52]

I have more weight numbers:
- H small plate by itself is 4lb-1.9lz (or ~4.1lb)
- Same plate with full DIR style harness, including crotch strap, knife sheav, but not knife is 6lb-0.3oz. => the full harness is 1lb-14.4oz (~1.9lb). That is with 2 stainless steel buckle, 5-ring harness, 2 2-ring crotch strap.

I don't include the actual webbing as it is near neutral, the stainless bits yes the webbing no for purposes of ballast calcs.

A basic hogarthian harness kit does not include a 2nd buckle either. Some use them some do not, and many like myself that dive with very little additional ballast use a plastic buckle to constrain the can light.

Tobin

 

[Storker]

Er, ah, well, if you read the OP you will see he is 1) in New York and 2) planning on 2 x 100 cu ft tanks.

If that's what you really meant, I'd probably limit my statements a bit from the beginning if I were you.

Initially, you said "Doubles implies staged deco", i.e. a vast generalization which I challenged. Now you're more or less saying "Double 100s implies staged deco", which is a slightly different kettle of fish. And I don't disagree with that, since a twin 100 cuf rig holds pretty much the same amount of gas as the D12x232 set I was talking about. A double 100cf rig is way to big and heavy to be a good alternative for no-stop diving. Unless the diver is a masochist...