BP/W HP100 vs AL80 weighting

[halocline]

Using the wing lift calculator often linked on SB, I entered the two extremes I could possibly be in. I used 10# head weight, -1 for DSS kydex plate, -1 for a light or other stuff (camera, hunting gear etc).

I don't know what you mean by "10# head weight", can you explain?

I'm not sure what you are trying to determine, is it whether to get a steel or kydex plate? Or is it what size wing to get?

Most divers would be substantially overweighted with no exposure suit, a HP100, and a steel plate. Most would not with an AL80. (The plate basically compensates for the +4.4 of the tank) If, in your normal suit, you use 4-6 lbs with a HP100, you'll probably be slightly overweighted with that suit and a SS plate, but not by much. You're going to add 5lb (more or less) of negative buoyancy and lose whatever positive buoyancy your BC has. You might check that by emptying it, and trying to sink it in a pool with weights in the pockets. It could take 3-4 lbs to sink.

I guess if you are mostly planning on using the HP100, a kydex plate would be a better bet for you. If you're mostly using AL80s, only occasionally using the 100 with your 2/3 suit, it's a different story.

 

[stuartv]

I don't know what you mean by "10# head weight", can you explain?

I'm not sure what you are trying to determine, is it whether to get a steel or kydex plate? Or is it what size wing to get?

10# head weight means the lift you need from your wing in order to keep your whole head up and out of the water. That is wing lift capacity that is in addition to counterbalancing the weight of your rig. Your wing would be suboptimal if it would only keep you neutral at the surface (i.e. the top of your head just touching the surface).

Since his post is all about using the wing lift calculator spreadsheet, it has been my assumption that he is trying to figure out what wing to get. But, that IS just my assumption.

 

[Mouth Breather]

Thanks guys for your inputs. You're both right, trying to determine wing size and ballast / plate material. I really don't use more than a 2mm most of the year. When I started adding things up it became obvious (as stuartv points out) that a HP100 with no suit and any backplate will be overweighted to some degree. Your inputs helped me confirm that.
I'll test the buoyancy of everything then give Tobin a call. He will probably clear all this up for me too but I like to do my homework and maybe reduce the stupid questions by 50%.

 

[seeker242]

Using the newer sheet, I'm -14 on descent and -6 at a 10ft safety. With a 26lb wing, I'd be filling it up to keep my head above water at the start. I shared the spreadsheet with these numbers if you want to take a look: LINKY

I've been playing with this calculator for a couple weeks now and no matter what I do with it, I can't get it show neutral at the SS with a steel tank with just a skin. Even if you drop the 2 lbs of trim weight that you are including, it's still -12 and -4. The only way I can get it to balance, with a steel tank, is to wear at least +7 lbs exposure. Let me know if you figure it out, ha!

 

[stuartv]

If you are only concerned about single tank diving, I will throw this out there. I now have dedicated rigs for single and double tank and I am seriously considering getting one of these back plates to replace my current dedicated single tank BP.

Store - Vintage Double Hose

It's only $75. It's aluminum. I don't know what the buoyancy is, but it can't be much. It was designed to allow use of a double hose reg, but it will work with a normal 1st stage. And it puts the tank right down against your back, instead of 1" or 2" or more away.

If I get one, I'll just mount trim weight pockets on the tank straps and use trim weights as necessary for ballast.

 

[Mouth Breather]

I've been playing with this calculator for a couple weeks now and no matter what I do with it, I can't get it show neutral at the SS with a steel tank with just a skin. Even if you drop the 2 lbs of trim weight that you are including, it's still -12 and -4. The only way I can get it to balance, with a steel tank, is to wear at least +7 lbs exposure. Let me know if you figure it out, ha!

The very reason I started this thread. It's that damned gravitational pull doing it I'm afraid, no way around it other than to add buoyancy. It surprised me too, as I said I take 4lbs with me with an older 2/3 full. My jacket must have more buoyancy than I would have thought. I'm going to find out just how much this weekend.

 

[sunnyboy]

I've been diving a BP & wing since 2003. Recently I bought an HP 100 (worthington, steel) but when teaching I have had to use AL80's as well. What I have found is that when I swap the HP 100 for an AL80 I must add 2x4lbs (8 lbs total) to the rig to get the same buoyancy. I have a cam band with two weight pockets on it for that purpose. I just put the two 4's in the pockets and strap the cam band to the middle of the AL 80. That way the actual rig and the DUI weight harness never change.

 

[Mouth Breather]

I've been diving a BP & wing since 2003. Recently I bought an HP 100 (worthington, steel) but when teaching I have had to use AL80's as well. What I have found is that when I swap the HP 100 for an AL80 I must add 2x4lbs (8 lbs total) to the rig to get the same buoyancy. I have a cam band with two weight pockets on it for that purpose. I just put the two 4's in the pockets and strap the cam band to the middle of the AL 80. That way the actual rig and the DUI weight harness never change.

With what suit?

 

[sunnyboy]

With what suit?

A drysuit, but that's irrelevant to the discussion. All I'm changing is the tank, so the weight difference is due entirely to the tank change.

 

[Mouth Breather]

A drysuit, but that's irrelevant to the discussion. All I'm changing is the tank, so the weight difference is due entirely to the tank change.

Very relevant to this thread, which is more about the inherent buoyancy needed to dive a bp/w with a steel tank. You have it in your drysuit, whereas most of us in my area are in 1-2mm if that.