How much BC lift do I require?

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Roo,

Understand your concern about calculating suit bouyancy / loss of bouyancy. It may be difficult to calculate, but one should be able to make an "estimate" of the loss of bouyancy.

The initial post in the thread was looking for a way to know if his planned wing had enough lift. I guess I was just trying to suggest that the 36# wing seemed to be more than adequate given the information in the original post - and I still believe that to be the case. However, using your approach a larger wing would be indicated assuming that a 2.0 FOS was to be maintained.

Good discussion!

Paul
 
Scubaroo:
HOW do you easily calculate suit loss without actualy getting wet and testing the suit seperately on the surface and at depth. Manufacturers certainly don't publish suit buoyancy statistics, and it can decrease as neoprene ages with use. Why bother if there's a rule of thumb that can be used that's sufficient.

I always figured that you determine total buoyancy of the suit on the surface and then assume that it's all gas so that at 2 atm it would compress to half thickness and half its surface buoyancy, etc. Obviously, this won't be completely accurate but it should work ok for most purposes. Having said that, I think the lift I need to offset gas and suit compression is less than the lift I need to sit on the surface in rough seas.
 
I thought I'd put my .02 in:

Here in the PNW I'm the only wetsuit diver I know! It's a 7 mm suit, and after the rescue diver course in a jacket style BC that advertised 42# of lift, I decided that #1 42# is not 42 # when the bc is a jacket style bc. It simply sqeezes your chest to the point you can't breathe!!

If nothing else I realized that there isn't a such a thing as "too much lift". Who cares if you have 80# (like I do) or 100#, if you can stay comfortably on the surface. What are you worried about? Drag? Hah!

Too much is definitely better!
 
unfix8r:
Who cares if you have 80# (like I do) or 100#, if you can stay comfortably on the surface. What are you worried about? Drag? Hah!

Too much is definitely better!


I disagree.

Firstly, having a huge wing DOES cause an amazing amount of drag underwater. It creates a lot of resistance, making it difficult to keep up with your buddies while you're diving. To keep up, you have to work harder, and so you breathe heavier and thus use your gas faster. Additionally, diving in a current gets near impossible because of all of the drag you have in your rig. Remember, a freediver equipped with fins can only sprint to 4 knots underwater... It's much less with gear on. In fact, in a recent Rodale's Scuba Diving magazine, there was no diver tested that could exceed 2.8 knots underwater in a single tank and wetsuit. None of them were able to MAINTAIN more than 2.2 knots, even at full effort. So yes, drag plays a huge role in your diving. A little more streamlined can go a long way in terms of gas consumption, effort spent, the speed at which you can cruise, and in the case of a current, your ability to stay in one spot.

Secondly, large bladders tend to be "all over the place," and a gas bubble within tends to travel to the point which is furthest from your body. So... Large bladders tend to tilt you one way or another, in a situation I called "opinionated BC's" in this article: http://www.DeepSouthDivers.org/homebc.html

Lastly, large bladders tend to "wrinkle" when you're diving with them, trapping gas bubbles inside... So they're more difficult to dump completely. To compensate, divers often wear more weight than they need to, once again adding to the effort spent while diving. (Not to mention that typically the weight isn't well - placed, making the "opinionated BC" problem worse...)

In short, yes... Having too much lift can be just as bad a problem as having too little.
 
When I switched over to my dry suit I was amazed to find out that I rarely added air to my BC. Then I go to thinking about it, and it made sense. The BC was just compensating for the air in my tank and anything else I had with me that was negative buoyancy.

The dry suit stays roughly the same buoyancy throughout the dive, give or take a bit. You go deep, you add air and you buoyancy stays the same, go up you let out air.

Granted, you should have enough lift to exceed your weights you are carrying in case you put a major hole in the suit or flood, and enough to keep you on the surface. But in general you shouldn't need much at all in the way of air in your BC.
 
https://www.shearwater.com/products/swift/

Back
Top Bottom