Question about experimenting with weighting

[ssssnake529]

Newbie question:

When you are on a boat dive trip with new equipment that will affect your weighting, how do you make adjustments to your weight?

We recently returned from a trip to Jamaica (our first time diving in salt water since we were certified.)
There were some weights available on the boat that we could stuff into our BCDs, but no real opportunity to test out various amounts of weight. When the dive began, everyone just jumped off the boat and began following the dive master.

What do you do in such a situation if you jump off the boat and end up just bobbing on the surface like a cork (wth an empty BCD?)

What do you do if you jump off the boat and sink like a stone?

I'm pretty sure both my wife and I are over weighted, but we figured it was better to sink than to not be able to sink.

On our next dive trip, we will both be diving in different configurations (no wetsuit for her, new BCD for me,) so our weighting will be inconsistent with our last trip. I've looked up various dive weight calculators online, and they provide such varied results that they are not very useful except for giving very gross approximations of how much weight we might need.

I'm hiring a private dive master on our next vacation and I'm considering spending some time at the beginning of our first dive just experimenting with different amounts of weight to see how much we actually need. (Not something I could do on our last trip, where we just needed to follow the group.) How do I experiment with weighting when I'm in the ocean floating around? In the pool it was easy. There was a pile of weights on the pool deck and I could just grab them or put them back as I experimented. If I dropped one, I could just reach down and pick it up off the bottom of the pool.

It seems like this process is a bit more complicated when the "pool deck" is a dive boat that's bouncing around in the ocean.

How do you make adjustments to your weight to account for new equipment/suit configurations? Do you take some time to work it out on a dive, or do you just make changes from dive to dive?

 

[TMHeimer]

I haven't been in that situation having always owned all my stuff, but will throw out some ideas.
-- Wetsuits-- I have 3 and know how much weight I need for each. This won't change--not enough to be a problem-- unless I change other equipment. Doing weight checks at home is probably the only way, meaning you rent the suit you think you'll need on the trip and get to a pool (salt water, add 5-6 pounds).
--BCD-- If you have your own you know what weight you'll need. If not, maybe put a bit more than what you needed in the OW course just to be safe. If too much, you can then adjust for the next dive. Yes, better to be a bit overweight than underweight so you can easily do the safety stop.
--Keep in mind some of the rules, like 5 pounds more for an aluminium tank vs. steel or salt water vs. fresh.

 

[boulderjohn]

What you describe is a very common situation for newer divers. I went through all of that myself when I was a new diver. I would now like to tell you exactly what to do, but I don't know myself.

It really does suck that you often have no chance to try out your configuration before you dive with it. What you are describing--people grabbing more weight than they need and going with it because being overweighted is better than being underweighted--is a common condition, and if you ask many DMs for advice, that is exactly what many will do. But not all. In many cases, if you describe to a DM what you have done in the past, some will make a real effort to help you get it right.

As for bobbing on the surface, it happens enough that boats are usually ready to deal with it.

Most weight calculators that I have seen will overweight you. I just googled this one and put in my details from years ago when diving in salt water with a 3mm suit, a typical BCD, and AL 80. In those days I used 8 pounds, and I could have used less. This calculator told me I needed 19 pounds--nearly 2.5 times what I really needed.

If you are diving with a large amount of air in your BCD, drop some weight on the next dive. Keep that up until you can hold a safety stop with only a little air (nearly none) in the BCD

 

[scubadada]

Start out with the weight you think you might need, a little heavy is fine. On the first dive, ascend to the safety stop, let all the air out of your BCD, and see what you do. You should be neutrally buoyant at this point and able to do a nice, slow ascent to the surface. If you are heavy, take off some weight and try again. If you happen to be light, add a little weight and try again. It does not take long to find out your ideal weight for all combinations of exposure protection, cylinders, etc. Keep track of these things in your dive log.

You are always going to be heavy at the start of the dive, The gas you are going to breath down during the dive weighs 5-6 lbs or more, depending on the cylinder volume.

 

[tursiops]

Start out with the weight you think you might need, a little heavy is fine. On the first dive, ascend to the safety stop, let all the air out of your BCD, and see what you do. You should be neutrally buoyant at this point and able to do an nice, slow ascent to the surface. If you are heavy, take off some weight and try again. If you happen to be light, add a little weight and try again. It does not take long to find out your ideal weight of all combinations of exposure protection, cylinders, etc. Keep track of these things in your dive log.

This is good advice, but what is missing is the 6-pound variable of the weight of the air in your (typically 80 cuft) cylinder, which is about a pound per 500 psi. Since you want to surface with 500 psi left in your tank, that means you might use as much as 5 pounds (2500 psi) from your tank. Thus, if you are neutral at the your safety stop at the end of the dive, you might be carrying 5 pounds less weight than you were at the beginning of the dive. Conversely, this means you will ALWAYS be heavy at the beginning of the dive, by the weight of the gas you haven't used yet.

Additionally, how full your lungs are can easily make a 4-6 pound difference, even more in some people.

What does this mean? It means when you do your empty-BCD weight check at the end of the dive, at your safety stop, log how much gas pressure you still have in your tank. it means fill your lungs all the way (get more buoyant) and see if you rise; empty your lungs and see if you sink. If you can rise and sink like that from a neutral postiion, then you are within a few pounds of the "right number."

 

[cmrangel]

A fairly quick and dirty way to do a check at the start of the dive is to empty your BCD, take a half of a breath and remain vertical without finning hands or feet. You should sink to about the middle to top of your mask or about half your head. If you sink more, you may be over weighted but a check at the end of dive at your safety stop will tell. If a lot of your head is out of the water, you likely need more weight. This is a rough guide, and I have used it when I have made changes. It will not take the place of checking at the end of the dive at your safety stop as described above but can at least get you close at the start of the dive.

 

[Jayfarmlaw]

The best route is to do a check out dive when you get to your destination. If that’s not an option, do a pool dive before you leave then adjust 4 ish pounds for salt water and work from there. Every DM I have dove with always carries a little extra weight on the first dive with new customers. When I dive with our travel group, I carry 2 extra 2 pound hard weights just in case someone wants to cork mid way through the dive.

There is nothing wrong with being a little heavy. You may use a little more air and fight your trim a bit but 4 pounds is not the end of the world. With no wetsuit, your wife will use less weight.

Hiring a private DM is a Genius move. He can carry extra weight if y’all need it and he can take weight if you have too much. If it’s not a live boat dive, he can get you squared away before you begin your dive. I imagine you will get more out of one dive with a private dive master than you will in a weeks worth of diving on your own.

Safe travels,
Jay

 

[tursiops]

Hiring a private DM is a Genius move. He can carry extra weight if y’all need it and he can take weight if you have too much. If it’s not a live boat dive, he can get you squared away before you begin your dive. I imagine you will get more out of one dive with a private dive master than you will in a weeks worth of diving on your own.

^^^THIS^^^

 

[tursiops]

A fairly quick and dirty way to do a check at the start of the dive is to empty your BCD, take a half of a breath and remain vertical without finning hands or feet. You should sink to about the middle to top of your mask or about half your head. If you sink more, you may be over weighted but a check at the end of dive at your safety stop will tell. If a lot of your head is out of the water, you likely need more weight. This is a rough guide, and I have used it when I have made changes. It will not take the place of checking at the end of the dive at your safety stop as described above but can at least get you close at the start of the dive.

I've never actually understood advice like this. You say, float with your head half out of the water. Since at the beginning of a dive, you are 5 pounds heavy (to account for the air you haven't used yet), this implies the top half of your head supplies at least 5 pounds buoyancy. Now, a quart of air instead of a quart of salt water gives about 2 pounds buoyancy....so you are saying the volume of the top half of your head is at least 2+ quarts and is completely empty?

 

[DeltaWardog]

If I can do a quick shore dive at my destination I will sometimes do that to do a weight check if I feel the need.

Another time I was diving warm water with a 3 mil for the first time and just told the DM on the boat "Hey I want to do a quick weight check after we get in before we start the dive". He was fine with it. Took all of a minute.

Communicate your needs with the DM! They want to help you.