Formula for estimating wing size?

[scubadiver888]

Found it, I had seen it sometime back.

Its by @DevonDiver

http://www.scubatechphilippines.com/wing-lift-calculator.xls

The spreadsheet is hosted by DevonDiver but the actual creator of the spreadsheet is listed in the file. It is Constantin Novoselsky (cnovoselsky@hotmail.com). We should give credit where credit is due.

That said, this spreadsheet asks for things like "Head Weight" and "Suit weight". I KNOW my cold water rig requires 27 pounds to float. If I use my 25 pound wing, my gear slowly sinks. If I use my 27 pound wing my gear floats at the surface without me in it. I took guesses at what the numbers should be for the things I didn't know (head, suit, etc.) and most the time the spreadsheet was telling me from 18 to 23 pounds of lift.

This spreadsheet is overly complicated.

Darrell

 

[decompression]

Tobin, I couldn’t agree more,
2 things the wing does;
1. Float your gear at the surface
2. Compensate for the weight of air you bring with you.

So, simply add up the negatives (air, steel tank, backplate, lead etc.) this gives you X
If you Dive drysuit, stop here and ensure that your wing lift is great than X
If you dive thin wetsuit, also stop here, wing must be greater than X
If you dive thick wetsuit shallow, stop here, wing must be greater than X
If you dive a thick wetsuit deep (60’+) consider using a drysuit but if you must then estimate buoyancy loss of suit, 50% for double 7mm, 25% for 7-5mm, usually 10-15 lbs, add this to X= equals the wing lift required.

X (20lbs)+ 10 (5 mm wetsuit)= 30 lbs

 

[hammet]

Tobin, I couldn’t agree more,
2 things the wing does;
1. Float your gear at the surface
2. Compensate for the weight of air you bring with you.

So, simply add up the negatives (air, steel tank, backplate, lead etc.) this gives you X
If you Dive drysuit, stop here and ensure that your wing lift is great than X
If you dive thin wetsuit, also stop here, wing must be greater than X
If you dive thick wetsuit shallow, stop here, wing must be greater than X
If you dive a thick wetsuit deep (60’+) consider using a drysuit but if you must then estimate buoyancy loss of suit, 50% for double 7mm, 25% for 7-5mm, usually 10-15 lbs, add this to X= equals the wing lift required.

X (20lbs)+ 10 (5 mm wetsuit)= 30 lbs

I'm no instructor and don't have anywhere near 5,000 dives, but this is just plain wrong.
You add your weight to your rig so that you are NEUTRAL with zero air in your BC or wing.
If you are too buoyant you add weight and subtract if too negative or course. But at this point you are neutral! (not withstanding 5lbs or so for air not yet consumed). The weight of your rig is irrelevant. If your rig was too heavy, you would have added less weights. If your rig was light, you would have added more lead.

As I stated before and echoed by another poster here, the only relevant thing you need air in your bc or wing to compensate for is wetsuit compression and air that you haven't used yet.

 

[Dogbowl]

OP here. Great discussion but I can’t say I’m less confused.

Here’s what I’m trying to do. I want to figure out if my Transpac XT with Travel XT wing (25lbs) will be sufficient lift for a future trip. It’s a new rig and I won’t have access to salt water until that trip.

Previously, I determined that I needed 16 lbs to comfortably complete a safety stop in salt water. I was using my Oceanic Biolite at that time, which weighs approx 5 lbs and has approx 32 lbs of lift. I was also floating on the surface very comfortably.

The main thing I’m changing now is my bc. I’m switching my Biolite out for my Transpac. Will I have sufficient lift?

Here are my current variables:

Female
Weight: 145 lbs
Height: 5’4”
Wetsuit: Henderson Thermaxx full suit 5mm, size 8
Beanie: 3mm
Boots: 6.5mm Aqualung Superzip
Fins: Aqualung Hotshots (lightweight travel fins)
Regs: Deep 6 (7’ and 22” hoses)
BC: Oceanic Biolite (weighs 5.5 lbs, 32 lbs lift)
Weight required to do safety stop: 16lbs

New variables:
Transpac XT with Travel XT wing
Weight: just under 8 lbs
Lift: 25 lbs

2 lights: approx 1 lb total
Hood or hooded vest (3-5mm)

I originally didn’t think I’d have a problem with a 25 lbs wing in warm water, but I also did not realize at the time that I needed a whopping 16 lbs to hold a safety stop. Now I’m not so sure. Also, since it’s a liveaboard I’ll be going on, and diving upwards of 25 dives a week, I may end up adding a bit more neoprene such as a hood or hooded vest to the equation. So I want to be sure the 25 lbs wing will be sufficient.

Thank you very, very much!

 

[RyanT]

Hey Dogbowl: what kind of tank are you planning to dive? That can add a lot of variability in weighting. In reality though, for single tank diving, especially wearing a 5 mm wetsuit, a 25lb wing should be sufficient.

 

[hammet]

Dogbone,

When you get in the water, put on the same weight you had with your BC and do a buoyancy check with the wetsuit you plan to use. Make sure your wing is empty of air. Add or subtract weight so that you are neutral. I'm sure you know how do to this. If you are using a full AL80 for the check, you'll need to add about 5 pounds to your result that will compensate you for the air you use up during the dive so you are not overly buoyant at your safety stop. (Maybe 6lbs for an HP100 only because it holds more air... not because it is heaver) That's it.

Now you descend to say 100 feet. The five lbs of weight you added makes you 5lbs negative. and since you still have a full tank of air, you have to add air to your wing to account for this so you don't crash on the reef. Additionally, your 5mm will compress some. Let's say, to be very conservative, it compresses about 3mm. An average size wetsuit has about 2-3 lbs of buoyancy per mm. So if you lose 3mm of 'volume' on your wetsuit, your buoyancy will decrease by about 6-9 lbs. Let's again be conservative and pick the 9lb figure. Therefore, to stay neutral at 100', you will need to add enough air so that you have 5lbs of lift for the weight of the air still in your tank plus 9lbs of lift required to offset the compression in your wetsuit. That gives you a total of 14lbs that you need assuming your buoyancy check was done correctly.

As you continue your dive, you will use up the air in your tank and you will become about 5lbs more positve so at the end of the dive but before you ascend, you will vent air from your wing to compensate. You will still need 9 lbs of lift for your wetsuit that is still compressed. However, as you ascend, your wetsuit decompresses and near the surface, you will not need that 9lbs of lift from the air in your wing anymore so you need to let it out. At your safety stop, you should have virtually no air in your BC and be practically neutral. (Actually, you'd be just slightly heavy because your wetsuit is still compressed a bit at 15 feet).

When, you get to the surface, you should be exactly neutral and any air in the wing you now put in is just to keep you bobbing comfortably above the level of the water.

So the MOST lift you will actually need if you've done your buoyancy check correctly is 14lbs.

 

[Dogbowl]

Hey Dogbowl: what kind of tank are you planning to dive? That can add a lot of variability in weighting. In reality though, for single tank diving, especially wearing a 5 mm wetsuit, a 25lb wing should be sufficient.

Oops, yes! That’s important and I forgot! AL80. I suppose that’s the standard Caribbean tank. I’m going to Belize on a liveaboard.

 

[Dogbowl]

Dogbone,

When you get in the water, put on the same weight you had with your BC and do a buoyancy check with the wetsuit you plan to use. Make sure your wing is empty of air. Add or subtract weight so that you are neutral. I'm sure you know how do to this. If you are using a full AL80 for the check, you'll need to add about 5 pounds to your result that will compensate you for the air you use up during the dive so you are not overly buoyant at your safety stop. (Maybe 6lbs for an HP100 only because it holds more air... not because it is heaver) That's it.

Now you descend to say 100 feet. You still have a full tank of air so you have to add air to your wing to account for this. Additionally, your 5mm will compress some. Let's say, to be very conservative, it compresses about 3mm. An average size wetsuit has about 2-3 lbs of buoyancy per mm. So if you lose 3mm of volume on your wetsuit, your buoyancy will decrease by about 6-9 lbs. Let's again be conservative and pick the 9lb figure. Therefore, to stay buoyant at 100', you will need to add enough air so that you have 5lbs of lift for the weight of the air still in your tank plus 9lbs of lift required to offset the compression in your wetsuit. That gives you a total of 14lbs that you need assuming your buoyancy check was done correctly.

As you continue your dive, you will use up the air in your tank and you will become about 5lbs more buoyant so at the end of the dive but before you ascend, you will only need 9 lbs of lift for your wetsuit that is still compressed. As you ascend, your wetsuit decompresses and near the surface, you will not need that 9lbs of lift from the air in your wing anymore so you can let it out. At your safety stop, you should have virtually no air in your BC and be practically neutral. (Actually, you'd be just slightly heavy because your wetsuit is still compressed a bit at 15 feet).

When, you get to the surface, you should be exactly neutral and any air in the wing you now put in is just to keep you bobbing comfortably above the level of the water.

So the MOST lift you will actually need if you've done your buoyancy check correctly is 14lbs.

I can most certainly check weight via trial and error when I’m there, but I want to know before I leave whether my 25lbs wing be sufficient. If not, then I won’t bring it and will bring my other bc instead.

 

[hammet]

I can most certainly check weight via trial and error when I’m there, but I want to know before I leave whether my 25lbs wing be sufficient. If not, then I won’t bring it and will bring my other bc instead.

If you read my example above carefully, you will see that the lift you need is ONLY DEPENDENT ON THE WETSUIT YOU ARE WEARING AND THE GAS YOU CONSUME!!!

If the inherent buoyancy of your BP/W is not the same as your previous BCD you will have to compensate by adding or removing weight so that you can be neutral at 500psi. But this weight DOES NOT AFFECT THE LIFT YOU NEED!!!! If you had to add weight, you are just canceling out the fact that your new rig is more inherently buoyant than your old one. Since your new rig is about 3lbs heavier than your old BC, you will probably need to drop about that much off your weight belt, but it still doesn't change how much lift you need.

 

[RyanT]

@Dogbowl, a 25lb wing will be plenty of lift using an AL80 in warm water. You may indeed need to do a weight check to get everything squared away, but the 25 lb wing will be plenty.