18 lbs Vs. 26 lbs??????

[SeaFlea]

thx for your input, you are most experienced in these matters.

most if not all of my dive setups are with no suit and weights attached to the bp/wing harness. i found on my most recent trip that with the bp/sta i needed 4 lbs to properly weight myself. that was with a AL80. with a steel tank i would guess i could get by with 2 lbs or less.

with that being said, back to my question. with my current dive equipment setup it seems to me, to have my wing keep me and my gear afloat ON THE SURFACE i've got to be coming close to a 18 lb wings ability.

thx again, seaflea

 

[DA Aquamaster]

Assuming you are close to neutral in your swim suit and are not using an exposure suit, then what you really need to offset is any negative buoyancy from regs, wing, BP, etc, as well as the negative buoyancy of a *full* tank along with any weight required to hold your safety stop at the end of the dive with a near empty tank.

What often gets left out of the caclulations is how much lift you need to keep the average 15 pound human head above water if you surface early in the dive. In my opinion, in the vast majority of cases, an 18 pound wing won't cut it if keeping your head above water with a full tank is a consideration.

A 26 pound wing should be about the minimum in my opinion, but then I have never drank the "tiny wing is better" kool-aid.

-----

-9 lbs for a BP wing and STA seems excessive for dives with no exposire suit. Stainless steel is as heavy as it gets as no one has yet developed a need for depleted uranium back plates. So I assume you have a stainless steel plate or perhaps are using a really heavy STA.

If you are not using an expssure suit an aluminum back plate and a lightweight STA would be adviseable to keep the non ditchable weight to a minimum. It will greatly expand your tank options. From the airline travel perspective, it makes more sense to have a 2 lb AL plate and add 4 lbs of lead at the destination than to haul a 6 lb SS plate all the way there.

An AL 80 is about 4 pounds positive when empty, so it sounds like you currently only need the weight to stay down with an empty AL 80. If you swtich to a steel tank you will find many of the tanks in the 85-100 cu ft range are around 1-2 pounds negative when empty, which would leave you slightly over weighted even with no ditchable weight.

The other concern is that you need that much weight with no exposure suit. You could just be floaty by nature, but be sure you are not unintentioanly kicking on the surface and are using extra weight you don't really need in order to compensate. If that is the case, then you are needlessly over weighted already.

 

[GrumpyOldGuy]

Have you compared the price/size/weight between the wings? Despite the 44% increase in buoyancy you might find the other parameters about the same. The 26lb wing is going to be a lot more versatile choice if it is your only unit.

 

[Bonairetrip]

Well actually, in a worse case scenario the wing does need to support me and and all my attachments / equipment. i'm not sure I would want to ditch any of my equip. if left on the surface for a extended period of time.

After all, what else do we have to remain afloat if left to our own devices? Are you suggesting going for a nice long swim towards the the best option?

thx for you insight,

SeaFlea

Of course it needs to and that is what my (b) test does. Note the highlighted text above: it needs to support you (including your suit) and your equipment as a single unit. In your calculations, you are implicitly assuming that just you, wearing your wetsuit, are neutral at the surface.

Perhaps an example will illustrate my point. There are two divers, diver X and diver y. Both dive only in swim trunks and shirt. They use the exact same reg and tank. And plate and any STA or lights. At the end of the dive, they are both perfectly weighted with no air in their cell.

The only difference is diver x has a weight belt of 10 pounds and diver y has no weight belt at all. Under your approach, they would require different size rigs. How does that make sense?

For the scenario you describe above, the (b) test I provided earlier above more than covers you. Think about it -- if the wing can lift you when your gear is the heaviest (full tank tank) and your suit bouyancy is at its worst (wetsuit compression), it will float you at the surface.

I know this is contrary to what instructors used to say (the old rule: your BC lift needs to equal your weight belt plus 10). But if you think about it, your kit needs to do three things: a) you need to be able to take it off at the surface and not have it sink; b) it needs to compensate for any change in bouyancy; c) float you at the surface. If you calculate (a) and (b) properly, (c) is a given. (Note: my analysis would be different with a drysuit and I would add a bit of a fudge to (b) iff I was not wearing a wetsuit).

As Tobin noted below, the two largest variables we need to do the calculation (suit and tank config) we don't know...so it is still not possible to answer the question of the OP.

 

[Bonairetrip]

Assuming you are close to neutral in your swim suit and are not using an exposure suit, then what you really need to offset is any negative buoyancy from regs, wing, BP, etc, as well as the negative buoyancy of a *full* tank along with any weight required to hold your safety stop at the end of the dive with a near empty tank.

I generally agree.

That said, the OP was suggesting 9# of plate/sta and another 4# of lead. That would make him negative at the start (full tank) and the end of the dive (empty tank). A better choice there would be Kydex/Aluminum and less (or no) lead.

 

[cool_hardware52]

thx for your input, you are most experienced in these matters.

most if not all of my dive setups are with no suit and weights attached to the bp/wing harness. i found on my most recent trip that with the bp/sta i needed 4 lbs to properly weight myself. that was with a AL80. with a steel tank i would guess i could get by with 2 lbs or less.

with that being said, back to my question. with my current dive equipment setup it seems to me, to have my wing keep me and my gear afloat ON THE SURFACE i've got to be coming close to a 18 lb wings ability.

thx again, seaflea

If you need 15 lbs of total ballast when diving with no exposure suit and an al 80 cylinder I would guess you are substantially over weighted.

If we take 15 lbs (plate, sta, reg and 4 lbs of lead) and subtract 4 lbs for the empty al 80 we still have 11 lbs of ballast.

People are made mostly out of water, and most people of normal stature will be close to neutral in just their swim suit.

I'd recommend a careful weight check. +11 lbs in your swimsuit is off the charts.

Proper weighting is key, bigger wings are not the solution to being overweighted.

Tobin

 

[Bonairetrip]

most if not all of my dive setups are with no suit and weights attached to the bp/wing harness. i found on my most recent trip that with the bp/sta i needed 4 lbs to properly weight myself. that was with a AL80. with a steel tank i would guess i could get by with 2 lbs or less.

with that being said, back to my question. with my current dive equipment setup it seems to me, to have my wing keep me and my gear afloat ON THE SURFACE i've got to be coming close to a 18 lb wings ability.

I would agree if you, without any gear, are neutral. Lets assume that you, just in your bathing suit are 10# bouyant. If you put on on a 5# weight belt, and nothing else besides your weight belt and bathing suit, do you still float? Or would you need a 5# wing to stay afloat?

That said, it seems like the smaller wing may lack the lift to float just your gear without you in it. If you have 16# in regs/plate/sta/attatched lead/ (OP figures) and you add a full tank (Luxfer S80 is - 3.6), you are now looking at the 26# wing in any event...

 

[hg frogman]

But if you think about it, your kit needs to do three things: a) you need to be able to take it off at the surface and not have it sink; b) it needs to compensate for any change in bouyancy; c) float you at the surface. If you calculate (a) and (b) properly, (c) is a given.

I agree with your points a), b), c).

I disagree with your assumption that a) and b) implies c). At least, it doesn't work well for me. My 30 lbs wing gives me enough support at the surface, while my 18 lbs is barely adequate. Of course, it depends upon one considers "adequate". For shore dives in a flat lake with no waves (for example) it may not be an issue.

I believe DA Aquamaster made the point all right in his post (as usual) : your rig has to float you with your head well above the water.

The discussion about bigger wings not a solution for being overweighted, though likely to be relevant, is another matter.

And finally a 30 lbs wing is more versatile (can work well with different suits, different tanks, etc) with no noticeable added drag, at least from my experience.

 

[SeaFlea]

Wow, thx for all the input. I do appreciate your insight.

Well, I can say that 13 lbs is what I need to maintain 15-20ft during my safety stop. the first day of my last trip I took my new BP/W (a 6lb ss backplate and a 3lb sta) and did a buoyancy check. Being quite comfortable with shorts and tee in 84 deg water, i found 2lbs was just shy and 4 was just right. Out of the NORM, but nonetheless true.

I agree with several folks that while 18 lbs of lift may be adequate, if not barely adequate for me, i would prefer to have abit of margin into the positive direction. the 26lb wing is a better choice, for me.

Thx to all for their time.

Good Dives, SeaFlea.

 

[cool_hardware52]

Wow, thx for all the input. I do appreciate your insight.

Well, I can say that 13 lbs is what I need to maintain 15-20ft during my safety stop. the first day of my last trip I took my new BP/W (a 6lb ss backplate and a 3lb sta) and did a buoyancy check. Being quite comfortable with shorts and tee in 84 deg water, i found 2lbs was just shy and 4 was just right. Out of the NORM, but nonetheless true.

I agree with several folks that while 18 lbs of lift may be adequate, if not barely adequate for me, i would prefer to have abit of margin into the positive direction. the 26lb wing is a better choice, for me.

Thx to all for their time.

Good Dives, SeaFlea.

Personal buoyancy doesn't change with depth, and does not need to be compensated for.

We use Buoyancy Compensators to compensate for things that change......

Personal buoyancy will impact total weighting, however if you mount the ballast required to offset your personal buoyancy to your person, and not your rig it will not impact the size of the required wing.


Assuming you were using an al 80 and it was near empty during your weight check you are ~+9 lbs in your trunks. That is not the norm. I suspect you may gas trapped in your current wing.

Tobin