Master Neutral Buoyancy: The Importance of Horizontal Trim (Simple Vector Physics)

[Neilwood]

Loving this topic.

Such an easy way to explain the principles to people.

 

[DelrayDM]

I think you should put a bunch of us lard arsed divers in the water demonstrating trim and buoyancy... and one slim person who learns trim and buoyancy

I am not slim anymore, but I volunteer/request to be that diver (or one of many). I'll drive quite a distance to do so. If someone can figure out how to keep my legs from sinking, I will be very happy. Any added weight must be easily dumpable.

I went to D.E.M.A. two years ago and went to every dive fin manufacturer, requesting buoyant fins. The most common reply was "you do not want buoyant fins". So much for listening to the customer. I do now use Dive Rite fins, which are slightly negative in salt water. If someone knows of buoyant fins, please let me know.

In fresh water: with 3mm full wetsuit plus another 3mm on torso, plus 3mm hood, I use no weight.

In salt water: no wetsuit, no weight.
In salt water: with 3mm full wetsuit 10-12 pounds.

But I have added 10 pounds of blubber since my last trip to fresh water.

 

[boulderjohn]

I am not slim anymore, but I volunteer/request to be that diver (or one of many). I'll drive quite a distance to do so. If someone can figure out how to keep my legs from sinking, I will be very happy. Any added weight must be easily dumpable.

I went to D.E.M.A. two years ago and went to every dive fin manufacturer, requesting buoyant fins. The most common reply was "you do not want buoyant fins". So much for listening to the customer. I do now use Dive Rite fins, which are slightly negative in salt water. If someone knows of buoyant fins, please let me know.

In fresh water: with 3mm full wetsuit plus another 3mm on torso, plus 3mm hood, I use no weight.

In salt water: no wetsuit, no weight.
In salt water: with 3mm full wetsuit 10-12 pounds.

But I have added 10 pounds of blubber since my last trip to fresh water.

After I had been working on tech diving for a while, I learned to hover horizontally using a BP/W and the techniques I mentioned earlier. At that time, I was still using my old recreational gear (ScubaPro Nighthawk) for single tank diving. I knew that I needed about 8 pounds of lead in salt water with a 3mm suit, and I further learned that if I distributed it equally (2 pounds each) in the Nighthowk's waist and shoulder pockets, I was in good trim. I went on a trip to San Carlos, Mexico, and on my first dive, I learned that the boat carried nothing but 4-pound weights. I thus had two choices--dive perfectly weighted with all the weights in the waist pockets, or dive with the weights distributed and be 8 pounds (100%) overweighted. I had always been a firm believer in being as properly weighted as possible, so having that much extra weight was anathema to me, but in my tech training I had gotten used to starting dives very overweighted with full steel doubles. I decided to go with 16 pounds of distributed weight, and I did not regret it. I was just fine.

Make sure you understand that I am not advocating being overweighted. I am saying that distributing weight to get yourself in good trim is also important, and you need to find the best possible balance using what is available to you. I read a horror story on ScubaBoard about someone taking a Peak Performance Buoyancy course in which the instructor kept adding weight to different places to get proper trim, apparently without realizing that it is also possible to take weight off in other places. The student was eventually pinned to the bottom, unable to move. That is not a good solution.

 

[Ayisha]

If someone knows of buoyant fins, please let me know.

I love my UTD Precision Neutral/Positive fins. They're neutral in fresh water, and slightly positive in salt water. The blade is similar to the jetfin, but it has a deeper, more comfortable foot pocket and they're each around 1/2 a pound lighter. It really helps in trimming out horizontally in addition to the other usual culprits: tank size, type and height on the back; distribution of weight/higher on the body; position of the arms more out in front; lifting the knees to be even with the tummy; lifting the feet higher behind you; adjusting how far out or how close your hands and your feet are to your body; being correctly weighted.

You can see the UTD Precision Neutral/Positive fins here as well as on their own and other sites: Precision Fins - Neutrally/Positively Buoyant - Dive Right in Scuba

 

[Patoux01]

I had always been a firm believer in being as properly weighted as possible, so having that much extra weight was anathema to me, but in my tech training I had gotten used to starting dives very overweighted with full steel doubles. I decided to go with 16 pounds of distributed weight, and I did not regret it. I was just fine.

My wild guess at this is that you'd have been just fine without those 8 pounds you added. Heck, I've even taken reef anchors with me on dives (or well, I found them half-way through the dive) and it didn't matter at all on my trim while I clipped those things off my chest d-ring...

 

[fsardone]

Heck, I've even taken reef anchors with me on dives (or well, I found them half-way through the dive) and it didn't matter at all on my trim while I clipped those things off my chest d-ring...

I would advice against diving with reef anchors and other heavy objects attached to the diver , for safety reasons:
-in case of loss of buoyancy one more thing to dump before you can have a chance to fight to survive;
-in case of sudden disconnection a good way to start an uncontrolled ascent to surface.

Use a DSMB or lift balloon, and think if recovering such an object without a plan is worth the added risk.
Plan your dive and dive your plan!
This is the basic scuba discussion forum, and for a basic diver this is a no-no!

Cheers

Fabio

 

[kelemvor]

I'll post the second installment in a day or two on how to establish horizontal trim.

It's been 28 days, did I miss the second installment?

 

[The Chairman]

You have not! We had a website to re-launch in the interim. I am already in communication with LowVizWiz to see if we can take those videos this weekend. Thanks for asking!

 

[EJQ]

I'm not seeing anything but the first graphic in the original posting. Were they a casualty of the relaunch?

 

[mbwilliamn]

If someone can figure out how to keep my legs from sinking, I will be very happy. Any added weight must be easily dumpable.


I don't have a recommendation that adds dumpable weight, but the minimal weight should not be an issue. It sounds like your total configuration puts your center of balance too far toward your feet, so when you relax, you stabilize feet low. To use the least weight possible, you need to shift your center of balance toward your head. A couple of basic options before adding weight. 1. Move your BC down on your tank. 2. Use AL tanks vs Steel. 3. Clip off dive lights higher up on your gear. 4. don't dive a shorty, or Jacket wetsuit, only ones with legs. 5. Use a weight belt vice integrated weights....most integrated systems put the weight below the waist.

After all this, the best way to shift the pivot point (center of balance) forward is use of a tank weight. A 1 3/4 LB ankle weight fastened around the tank just below the reg provides a huge lever and for the minimal amount of weight provides the most change you can get.