First ocean water dive weight question?

[TMHeimer]

Start with the fact that people rarely do a competent weight check, and then, no, it is not the same. A proper weight check, whether done at the beginning of a dive or at the end, is different because a newer and less relaxed diver will hold air in the lungs unnecessarily, make unnecessary movements, and not adequately vent air from the BCD.

I am not just talking about beginners, either. When I was a relatively new technical diver, I would descend to may planned bottom depth and perfect my buoyancy as I swam along. Once I was satisfied with my buoyancy, I would concentrate on making sure I did not go through my air too quickly by getting into my Zen zone" of total relaxation. I would let all cares dissolve as I aimed for total relaxation. Within seconds I would drop about 10 feet and have to add air to my wing.

Understood. You have explained why some divers will in fact be able to lose weight after getting more experience. Makes sense. Of course, by definition, their first weight check was then not a proper one. I'm sure we agree on that.
Don't know what unnecessary movements or not adequately venting air has to do with a proper wt. check. Maybe I was lucky and just didn't do these things?
From the OW manual-- "Hold a normal breath"..... why would the less relaxed diver do something different? I guess they do.

back to jafo19D-- Getting a different type of BCD (or any different equipment) may only change the amount of lead you have to use. It doesn't decrease the total negative equipment weight you need. If your BCD is "heavier" some of the weight you previously had in lead is now part of the BCD. Just as hard to walk a quarter mile geared up.

 

[Jafo19D]

Understood. You have explained why some divers will in fact be able to lose weight after getting more experience. Makes sense. Of course, by definition, their first weight check was then not a proper one. I'm sure we agree on that.
Don't know what unnecessary movements or not adequately venting air has to do with a proper wt. check. Maybe I was lucky and just didn't do these things?
From the OW manual-- "Hold a normal breath"..... why would the less relaxed diver do something different? I guess they do.

back to jafo19D-- Getting a different type of BCD (or any different equipment) may only change the amount of lead you have to use. It doesn't decrease the total negative equipment weight you need. If your BCD is "heavier" some of the weight you previously had in lead is now part of the BCD. Just as hard to walk a quarter mile geared up.

When I got my own BCD I was able to dial in my weights better because each BCD is different. Plus the Hydros is neutrally buoyant compared to some jacket BCDs which I had rented before so that helped take off some lead as well.

 

[boulderjohn]

Don't know what unnecessary movements or not adequately venting air has to do with a proper wt. check. Maybe I was lucky and just didn't do these things?

There are two (more, really) ways to do weight checks. All standards call for doing weight checks BEFORE training dives. People on ScubaBoard are obsessed with doing a check at the end of a dive with a near empty tank, but you can't do that with a new situation. What every instructor I know does is tell the student to do the pre-dive weight check and then fine tune it at the safety stop.

The standard pre-dive weight check is done by keeping perfectly still and dumping all air out of the BCD while holding a normal breath, not a huge breath. In theory, you should float at eye level and then sink slowly if you exhale. If you don't dump all the air, you are not getting an accurate check. If you hold a deep breath, you are not getting an accurate check. If you kick continually (very common), you are not getting an accurate check. If you have air trapped in your system (very likely in the wet suit), you will not have an accurate check. Many books tell you to add weight to compensate for expected loss of air weight during the dive, but many others believe it is not necessary because enough trapped air will go away during the dive to make up for that weight loss.

Doing a weight check at the end of the dive is also plagued by trapped air, mostly in the BCD. In fact, I learned to prefer to be a few pounds heavy for this reason. If the air bubble at the end of the dive is larger than the tiny bit there when properly weighted, it is much easier to find it and maneuver the body so that the air in the wing can get to the proper escape point. Most new divers take a long time to realize fully that air wants to go up, so if you, for instance, hold your inflator hose down by your chest when you want to vent air, it does not do a lot of good. Most new divers swim at a 45° angle, and they fin constantly in that position. Sometimes it is nearly impossible to get them to stop, unless you can get them to dive in proper trim. If they are in proper trim, they too often don't realize that the rear dump is their friend.

Here is a story of my very first OW training dive as an instructor. It was on a shop trip to Key Largo, and I had 3 students I had not had for the pool sessions. (I was new then--it probably would not have made a difference.) The first dive then had no skills--you just dived to get the hang of things. Two of the students were doing just fine, but one was struggling, swimming at that 45° angle and finning constantly. Whenever he checked his console for his air--which I had emphasized they should do often--he would start ascending, because his feet were kicking him upward, causing his BCD to start to inflate (We were, of course pretty shallow.) He would then dump the expanding air, drop back down to us, and put more air back into the BCD to get neutral again--this is a very common sight with beginners.

One time that he ascended too far, he struggled to find his inflator hose, and he grabbed his snorkel instead. He held the snorkel high, pressed the bottom with his finger, and dropped rapidly down to join us. The other two students were visibly amazed. After the dive, it made a great discussion. Why had he descended after pressing the snorkel? Because he was relieved to have found it and had exhaled deeply as part of that relief.

 

[AdivingBel]

Have a conversation with your instructor and explain your situation before your dives then do what he/she says and adjust from there. It won't be their first rodeo and your situation is not unusual. They should have you do proper weight checks at some point to sort it out. I know you want to do your due diligence before your dives, but remember to be a student and keep an open mind. Have fun. All IMHO, YMMV.

 

[TMHeimer]

There are two (more, really) ways to do weight checks. All standards call for doing weight checks BEFORE training dives. People on ScubaBoard are obsessed with doing a check at the end of a dive with a near empty tank, but you can't do that with a new situation. What every instructor I know does is tell the student to do the pre-dive weight check and then fine tune it at the safety stop.

The standard pre-dive weight check is done by keeping perfectly still and dumping all air out of the BCD while holding a normal breath, not a huge breath. In theory, you should float at eye level and then sink slowly if you exhale. If you don't dump all the air, you are not getting an accurate check. If you hold a deep breath, you are not getting an accurate check. If you kick continually (very common), you are not getting an accurate check. If you have air trapped in your system (very likely in the wet suit), you will not have an accurate check. Many books tell you to add weight to compensate for expected loss of air weight during the dive, but many others believe it is not necessary because enough trapped air will go away during the dive to make up for that weight loss.

Doing a weight check at the end of the dive is also plagued by trapped air, mostly in the BCD. In fact, I learned to prefer to be a few pounds heavy for this reason. If the air bubble at the end of the dive is larger than the tiny bit there when properly weighted, it is much easier to find it and maneuver the body so that the air in the wing can get to the proper escape point. Most new divers take a long time to realize fully that air wants to go up, so if you, for instance, hold your inflator hose down by your chest when you want to vent air, it does not do a lot of good. Most new divers swim at a 45° angle, and they fin constantly in that position. Sometimes it is nearly impossible to get them to stop, unless you can get them to dive in proper trim. If they are in proper trim, they too often don't realize that the rear dump is their friend.

Here is a story of my very first OW training dive as an instructor. It was on a shop trip to Key Largo, and I had 3 students I had not had for the pool sessions. (I was new then--it probably would not have made a difference.) The first dive then had no skills--you just dived to get the hang of things. Two of the students were doing just fine, but one was struggling, swimming at that 45° angle and finning constantly. Whenever he checked his console for his air--which I had emphasized they should do often--he would start ascending, because his feet were kicking him upward, causing his BCD to start to inflate (We were, of course pretty shallow.) He would then dump the expanding air, drop back down to us, and put more air back into the BCD to get neutral again--this is a very common sight with beginners.

One time that he ascended to far, he struggled to find his inflator hose, and he grabbed his snorkel instead. He held the snorkel high, pressed the bottom with his finger, and dropped rapidly down to join us. The other two students were visibly amazed. After the dive, it made a great discussion. Why had he descended after pressing the snorkel? Because he was relieved to have found it and had exhaled deeply as part of that relief.

Thanks for the details. Yeah I figured there are several ways to do a check, and yes it seems many on SB are obsessed with doing it with a near empty tank. There is also that you can really never be "perfectly" weighted except maybe for a split second when you breathe your tank down to that exact point.
I was lucky in that I don't recall ever swimming at a 45 degree angle when I was new (unless my old guy memory is fading). I think I figured out early on to hold the inflator way up and even tip to the right to get all the air out of the BC-- then later I read that this is what you should do. Then again, I've mentioned before that the first few times I cleared my mask I didn't look for a spot to kneel. I was very comfortable in water before the OW course--I guess that is also a plus when doing your first weight check (in fact, I don't recall doing one before my first checkout dive, but that was long ago).

 

[Seville]

I am very sorry I did not notice this before. Yes, that is the problem. He had one of those instructors who still teaches students negatively buoyant.

So sorry! Once you get away from that instructor and realize that scuba diving is done in mid water and not anchored to the bottom, you will find that the floaty feeling that made it hard for you to do those skills is actually the feeling you are supposed to have when you dive. It is called "neutral buoyancy."

When I used to teach in a warm pool with a 3mm shorty, I could have dived without any weight at all. Then I had to pose for pictures for an article on neutral buoyancy instruction, and I had to do comparison pictures of instruction on the knees, something I had not done in many years. In order to stay down to demonstrate the skills, I needed 12 pounds.

I once had a student from our shop come to me for the open water part of instruction, using a 7mm suit in fresh water. He had purposely done the pool session in a 7mm suit so he could get his weight right. His instructor taught him on the knees. He told me he had learned from that instructor that he needed 22 pounds with a 7mm suit. When he did his last OW dive, we had him down to 10 pounds, and he could suddenly feel what diving is supposed to be like.

Yes for all the drills we take a knee and do them. When i was trying to put my weights back in I was going backwards and on the side, so it looked really bad when i did it

 

[HKGuns]

I ran your numbers through the optimal buoyancy calculator and it says you should need 22 pounds in Salt water. Suggest you run the numbers yourself to better understand where to start. I used a generic 3K AL80 which may not be accurate.

I have found this to be an extremely accurate starting point for my weighting.

Optimal Buoyancy Computer