How Much Lift?

[squidster]

If your weight is 235LBS and you need 26-28lbs of weight with 7mm wet suit
how much lift do you need?
rofile: rofile:

 

[sea2summit]

Are you nutral with 26-28lbs of lead? Then none. Next find all of the boancy of your gear (i.e. tank -2 pounds empty, light -.5, fins -1 etc.) Add all of that together and the is the amount of lift you will need for saltwater I assume.

 

[squidster]

it takes 28 lbs to get me down under the water

 

[sea2summit]

With all your gear? Tank full or empty? Size/type of tank? BP/W or Jacket BC? Other gear?

 

[scarefaceDM]

Not enough info on your question.

In this case size matters. How tall are you, body type? Usng steel tank or Aluminium. Size of tank? what other gear are you using. (Light, reel etc) are your fins negative? How streamlined are you etc...this all takes importance in determining the lift you need.

As Sea2summit mentioned ...add all that gear up plus your weight in lead not your body weight.

Usually 40 to 60lbs of lift is sufficient. It all depends on how you dive and where you dive. Recreational diving runs about 30 to 55-60lbs of lift. Tech diving( diving with twin tanks) calls for 55 to 70lbs of lift. A drysuit is usually used and it is a redundant LIFT.( not to get into that discussion) SOme will swear by using 100lbs of lift with doubble bladder.

It all depends on your needs.

 

[cool_hardware52]

If your weight is 235LBS and you need 26-28lbs of weight with 7mm wet suit
how much lift do you need?
rofile: rofile:

Your weight doesn't matter.

Any BC has to meet two criteria;

Float your rig at the surface with you and your buoyant exposure suit in it,


And it needs to be able to compensate for the compression of your exposure suit.

Which ever of these two requirements is larger dictates the minimum lift required.

In cold water it's usually the compression of your suit.

You do not state if the 28 lbs you cite is just the lead you are using, or if it includes the tank, reg, (back plate if your using one) etc.

My recommendation is to take your exposure suit and roll it up and throw it in the pool. Add lead until it's neutral. Weigh the bag 'o' lead. This weight represents the initial buoyancy of your exposure suit.

Your suit cannot loose more buoyancy that it starts with.

You can estimate the weight of your rig. Look up the buoyancy of your tank, full, and add all the rest of the gear that on your rig, i.e. a couple lbs for a reg, any ballast on your rig like intgrated weights or backplates + can lights, reels etc.

Most likely in a 7mm the suit will be the determining factor.


Tobin

 

[MSilvia]

Off the top of my head, there only two things you need BC lift for.

The first is establishing buoyancy at the surface, and if you have just enough weight to stay submerged at the end of a dive, you'll be carrying extra weight at the beginning so you won't be underweighted at the end. If your tank is (for example) 2 lbs negative when full, and 3 lbs positive when nearly empty, you need 5 lbs of lift to stay neutral at the beginning of the dive, and a few more than that to be positively buoyant at the surface.

The second thing you need lift for is offsetting the loss of buoyancy you might experience if you dive deep in a wetsuit. As the suit compresses with depth, you'll need to add lift to stay neutral.

It doesn't matter how much you weigh, or how much lead you carry, so long as you are properly weighted. What's important is how your buoyancy will change over the course of the dive, and making sure you have adequate lift available to offset any tendancy to sink when you don't want to. Personally, I haven't run into any situation that required more than 30# of lift, except when I dive in my extremely negative double HP100s. For that, I use a 40# wing. IMHO, anything over 45# is ridiculously excessive unless you have either very unusual (and heavy) gear, or some special circumstance that dictates diving with severe overweighting and which cannot be managed through some more prudent approach.

 

[*Floater*]

it takes 28 lbs to get me down under the water

Maybe it does, maybe it doesn't. You are a new diver and new divers tend to use too much weight. Reasons for using too much may include buoyant BC's that trap air even when you want them completely empty, or trying to sink (without without finning down) at the start of the dive when your wetsuit is still dry and therefore more buoyant than at the end of the dive and may have some air trapped in it, and also not accounting for about 20% of wetsuit compression that happens during the first 10 ft.

Take a look at this article: http://dir-diver.com/en/knowledge/how_much_lead.html

There's a chart for the compression of an XL 7mm fullsuit. Notice that it's about 15.4# buoyant at the surface (about 12 or 13# at around 10 ft.), so I doubt you would need almost twice the weight to sink yours, though maybe an XXXXL Farmer John style suit made of new extra buoyant neoprene with thick hood, gloves and boots might take about that much.

Chances are you'll end up using less weight as you gain diving experience.

 

[cool_hardware52]

Maybe it does, maybe it doesn't. You are a new diver and new divers tend to use too much weight. Reasons for using too much may include buoyant BC's that trap air even when you want them completely empty, or trying to sink (without without finning down) at the start of the dive when your wetsuit is still dry and therefore more buoyant than at the end of the dive and may have some air trapped in it, and also not accounting for about 20% of wetsuit compression that happens during the first 10 ft.


There's a chart for the compression of an XL 7mm fullsuit. Notice that it's about 15.4# buoyant at the surface (about 12 or 13# at around 10 ft.), so I doubt you would need almost twice the weight to sink yours, though maybe an XXXXL Farmer John style suit made of new extra buoyant neoprene with thick hood, gloves and boots might take about that much.

Chances are you'll end up using less weight as you gain diving experience.

Neoprene varies widely, and the compression will vary with the age of the suit, and the number and degree to which it has been compressed. An old suit that's been to 130ft + repeatedly is pretty much "crushed neo"

I would agree that new divers are routinely overweighted. It's also quite possible to have a 7 mil suit on a large guy that's ~30 lbs positive. The less dense neoprenes, i.e. more voids, less rubber, are both more buoyant, and more prone to compression.

High density suits are expensive, and hard to don. Low density (super stretchy) neo suits are easier to put on, but offer less thermal protection. This often leads to users selecting a thicker suit, or added layers (hooded vests, core warmers etc.) That means MORE easily compressed, buoyant neoprene.

It's well to remember that the pressure doubles in the first 33 ft of depth. The voids in neoprene that make it both compressible and insulating can be expected to compress quite a bit in the first 33 ft.

That a key reason why maintaining buoyancy when shallow using a thick wetsuit is far more challenging than maintaining buoyancy at greater depth.


Tobin

 

[squidster]

I think your wright its experience thats needed, and knowing the weight of your equipment ,so most likley if i buy a bc that has a max of 50 lbs of lift i will cover myself.
Later with alot more experience i can change to something lighter if i want.
I dont think i would need more lift unless i was a tech diver which i am not.