Logistics for weight adjustment dive

[samsp]

So I want to do a dive to have a go at adjusting weight. I'm going on a trip shortly and need to work out the right weighting for AL80's, which I don't normally dive with.

So do I try it heavy and remove some weights during the dive? In which case what do you do with the weight? If you want extras what do you do with them?

How do you folks do this?

sam

 

[RIOceanographer]

Before you even get in the water you can calculate about how much more weight you should need when switching from whatever your normal tank is to an AL 80. This should get you very close, assuming your are already correctly weighted on your normal tank.

Look up the buoyancy when empty on whatever tank you have. This is usually listed on the manufacturer's website. The buoyancy of an empty Al 80 is about 4 lbs positive. The difference in buoyancy between the two is the about the amount you should add. If your normal tank is -1.0lbs negatively buoyant empty and the Al 80 is +4.0lbs positively buoyant empty then 4.0-(-1.0)=5.0lbs. In this example you need to add 5 lbs to your belt.

Really simple to do.

 

[Diver0001]

So I want to do a dive to have a go at adjusting weight. I'm going on a trip shortly and need to work out the right weighting for AL80's, which I don't normally dive with.

So do I try it heavy and remove some weights during the dive? In which case what do you do with the weight? If you want extras what do you do with them?

How do you folks do this?

sam

Why don't you use the technique they taught you in your OW course? I'm confused.

R..

 

[The Kraken]

samsp,
I'll try to answer your question without asking another or make inferences to poor training.

Start your dive slightly overweighted. Carry a collection/bug bag or some other receptacle that can be attached to your down line at your safety stop depth.

Dive your dive and try to be at your safety stop with 500 psi left in your tank.

When you've reached the 500 psi point, with your b/c deflated, remove only enough weight that will allow you to be neutrally buoyant with a normal breath.

At this point you should be able to take a deep breath and slowly ascend to the surface.

If you follow the main posts, you will logically deduce that one of the primary goals of neutral buoyancy is to be able to maintain neutral buoyancy at your safety/decompression stops.

 

[Charlie99]

If you are using the same exposure suit you normally dive with, as RIOceanagrapher say, you can just use the difference in tank buoyancy specs to get very close.

If you are changing wetsuit, then overestimate by a few pounds and stuff the extra weight blocks somewhere that you can remove them and hand them over to your buddy --- he should easily be able to support an extra 5 pounds or so.

You don't have to have a 500psi tank. Just figure that every 500psi in an AL80 weights about a pound. If for instance, you do a safety stop with 1500psi and hand weight off to your buddy until you are just right, then you need to add 2 (or 3) pounds to have the right weighting with a 500psi (or near empty) tank.

 

[donacheson]

So I want to do a dive to have a go at adjusting weight. I'm going on a trip shortly and need to work out the right weighting for AL80's, which I don't normally dive with.

So do I try it heavy and remove some weights during the dive? In which case what do you do with the weight? If you want extras what do you do with them?

How do you folks do this?

sam

If you've got a pool handy, it's easy. Just get into the shallow end with all your gear on and pick up enough weight off the bottom to get neutral with an empty BC while breathing normally. Then add 1 pound for each 500 psi in the Al80 and 2.5% of your total weight (you plus gear) if the pool water's fresh and you'll be diving in sea water.

If no pool, but the dive boat has a platform, you can move weights between it and your BC pockets until neutral with and empty BC, etc. As noted in another message, a buddy will do, too.

 

[donacheson]

Why don't you use the technique they taught you in your OW course? I'm confused.

R..

Just out of curiosity, what technique is being taught these days? (I was certified in 1978.)

 

[RIDIVER501]

When I am doing this I use a tire float with a cover or bin mounted in it as a base station.

I figure out my rough weighting based on tank and exposure suit then set my weighsystem for 80% adding the last 20% wth clip on weights incase i have to dump weight. then I get in water too deep to stand with the base station and do a bouyancy check....a little involved but the overall results are excellent.

 

[matt_unique]

So I want to do a dive to have a go at adjusting weight. I'm going on a trip shortly and need to work out the right weighting for AL80's, which I don't normally dive with.

So do I try it heavy and remove some weights during the dive? In which case what do you do with the weight? If you want extras what do you do with them?

How do you folks do this?

sam

There have been previous threads about what people write in their log book. Perfect example! Once you have done a trip you can look back to see what weight you used for a given location.

So this is your first trip into these conditions. Best way is to dive in similar conditions. If this is not possible talk to an instructor to get a rough idea or even the shop you will be diving with (ideal). Contrary to what most people say it is not a big deal to do a dive a little heavy. Get a suggestion from those familiar with the conditions to get an idea so you are not grossly over or under. You will probably dive more than 1 tank yes? If you are a little heavy - no big deal - you have a little more air in your BC. Remove small increments of weight over the course of your dives until you are right on then write it in your log book.

Always better to be a little heavy than a little light. A little heavy you have more air in your BC. A little light and you may not be able to stop at 15' with a low tank.

--Matt

 

[mccabejc]

Here's a link to a table showing the buoyancy of different tanks at different pressures in salt/fresh water. You should be able to find the exact difference in buoyancy, and that will tell you the difference in weight between what you use now and an AL80.

http://www.deep-six.com/page66.htm