New BPW setup - worry about lift capacity?

[jellycatsdad]

Bought my first BC, a BPW setup, it’s a Tulsa T-Wing. An off-the-shelf setup that’s close to the Hogarthian setup with a continuous harness, an aluminum dogbone backplate - but with shoulder straps and padding I can remove. The wing is a 27lb lift capacity one. I dive in Monterey - so I’m wearing a 7mm wetsuit with a 7/5mm hooded vest and either 15lbs(steel HP80s) or 24lbs(AL80s) of lead. My concern is the wing being undercapacity - I’ve talked to a few people who said I’ll be fine with the current wing - and BPWs are modular by nature. Should I be worried about this? For now, I‘m going to wear my ditchable weight on a weight belt and put 4-5lbs as trim weight.

 

[L13]

It should be enough capacity. The BC is not there to compensate for the lead you are carrying. It is only there to compensate for buoyancy CHANGES during the dive. The two main sources of buoyancy change during a (recreational) dive are:

• Gas breathed during the dive
  • (~4-5 lb for the tanks you have)
• Suit compression at max depth
  • (not sure in your case, but see: Optimal Buoyancy Computer)

 

[jellycatsdad]

It should be enough capacity. The BC is not there to compensate for the lead you are carrying. It is only there to compensate for buoyancy CHANGES during the dive. The two main sources of buoyancy change during a (recreational) dive are:

• Gas breathed during the dive
  • (~4-5 lb for the tanks you have)
• Suit compression at max depth
  • (not sure in your case, but see: Optimal Buoyancy Computer)

I was punching though the numbers with that spreadsheet - it said my BC if I have weight on it isn’t enough to lift my rig. Is that more of a concern in tech diving?

 

[Brett Hatch]

It's a concern for anybody, I think. I don't do tech dives, just recreational, but I want my rig to be able to float. So, I prefer to put roughly half of the ballast on a waist belt, and half on the backplate.

For example, 10-14 lbs lead on the waist. And then on the rig, 2-4 lbs lead in trim pockets, plus 5 pounds for a steel backplate, plus 8 lbs for a full HP100.

How much lead do you dive with? And, can you put some of it on your waist or on a harness, instead of on the rig?

 

[jellycatsdad]

It's a concern for anybody, I think. I don't do tech dives, just recreational, but I want my rig to be able to float. So, I prefer to put roughly half of the ballast on a waist belt, and half on the backplate.

For example, 10-14 lbs lead on the waist. And then on the rig, 2-4 lbs lead in trim pockets, plus 5 pounds for a steel backplate, plus 8 lbs for a full HP100.

How much lead do you dive with? And, can you put some of it on your waist or on a harness, instead of on the rig?

As it stands, I dive 15lbs with HP80s, 24 with Al80s. My plan was to have 5lbs on the upper cam band for trim and the rest on a weight belt. I plan on getting weight pockets for the waist strap down the road.

I‘m also trying to figure out why I’m having trouble decending - looks like I’m wearing less lead, next dive with a HP80 I’m going 18lbs, and maybe 25-26 with Al80s, I sunk too quickly with 26lbs of lead with AL80s.

 

[Brett Hatch]

OK, so most of the lead is on your belt, so don't worry about the floating your rig thing. With 27 pounds of lift on the wing, it can support roughly 27 pounds of ballast on the rig. You are bringing much less than that on the rig, so you'll be able to float it no problem. 27 pounds should be plenty of lift for any setup in this area, except maybe heavy double steels with a thick wetsuit -- but heavy doubles in a wetsuit is a bad idea in the first place, and doubles would need a different wing anyway.

Well, if you are getting that from comparing to my numbers, there's a grain of salt there. Because our bodies aren't the same, and I don't dive a 2-piece wetsuit, I either dive a one-piece 8mm wetsuit, or a drysuit. I guess my wetsuit would be the closest thing to your wetsuit... for that I use 16 pounds lead, 5 pounds from the steel backplate, and 1 pound from an empty steel tank. So call it 22 pounds total ballast.

Your aluminum plate is probably 1-2 pounds ballast, HP80 is about 1 pound when empty, so that plus 15 pounds lead is around 18 pounds total ballast. If you are having trouble sinking, especially if you're having trouble at the end of the dive, then yeah adding a few pounds lead is probably a good idea.

One thing I will point out with your numbers is that a 9-pound gap between HP80 and AL80 doesn't quite add up. An HP80 is about 6 pounds more negative than an AL80, so when you have your weight dialed in, I would expect a 6-pound gap between the two setups. Have a look at the tables in this thread for more info; the relevant quantity here is the buoyancy when empty.

 

[L13]

I was punching though the numbers with that spreadsheet - it said my BC if I have weight on it isn’t enough to lift my rig. Is that more of a concern in tech diving?

I'm surprised! your suit compresses more than 20 lb ?

 

[L13]

OK, so most of the lead is on your belt, so don't worry about the floating your rig thing. With 27 pounds of lift on the wing, it can support roughly 27 pounds of ballast on the rig. You are bringing much less than that on the rig, so you'll be able to float it no problem. 27 pounds should be plenty of lift for any setup in this area, except maybe heavy double steels with a thick wetsuit -- but heavy doubles in a wetsuit is a bad idea in the first place, and doubles would need a different wing anyway.

Exactly.

One thing I will point out with your numbers is that a 9-pound gap between HP80 and AL80 doesn't quite add up. An HP80 is about 6 pounds more negative than an AL80, so when you have your weight dialed in, I would expect a 6-pound gap between the two setups.

I suspect OP is over weighted.

 

[lexvil]

It will help with the wild guessing if you give us a general size idea so the surface buoyancy of your 7mm can be guessed at.


for me, Monterey diving I don’t care if my rig can float, I’m more concerned with me floating in a ditch the rig situation. I can ditch about 2/3 of my lead if needed.

let me Add, you picked the wrong set up for Monterey unless you are pretty small.

 

[johndiver999]

As others have said, if you have sufficient lead to drop, the wing should be OK. I personally would want around 35 lbs for that type of setup, but I prefer to have excess capacity for emergencies (assisting buddy) or bringing up something heavy from the bottom.

Try it out and see how you like it. If it is full and spitting air out the over pressure valve at 100 feet, then you might have to change something.