Overweighted?

MATTBIN · May 13, 2003

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Sundays sea dive brought home a question that I have been pondering a while. I have for a while wondered about the lead I am carrying, is it too much? During our first ascent I launched the smb, having wrapped my arm around the wreck to prevent being dragged up in error, dumped all the gas from the bcd and opened the auto valve. When I was reeling up I was definitely negatively buoyant so that I had to fin to keep ascending, I was in a vertical position. Ian on the other hand was nicely horizontal above me letting the line slip through his fingers. During the second ascent when Ian deployed I dumped the gas again and was positioned below him, sending my bubbles up into his face ocassionally, again having to fin to ascend, I also felt I was pulling at his kit as we were ascending (thanks Ian for letting me do that). So it seems to me on both occasions I was somewhat 'heavy'. I sink reasonably easily at the beginning of the dive.

I do find however when actually finning along a ledge at the end of the dive (say <10m) I have a tendency to go to the surface if I use less weight than my current set-up. When finning at the beginning of the dive I am negative unless I close the auto a few clicks and squirt some air in. I feel as if I could lose some at the beginning but need it at the end. The suit is membrane with a weezle, I dont feel I have floaty feet even though they are neoprene boots. So I am happy I dont have excess gas which makes me think I dont have excess lead.

Answers please as I would dearly like to be just right at the end of the dive as currently I feel if I loose grip of the smb I am going to sink, which of course makes a 6m stop in swell difficult to maintain.

Matt

Dr Stevil · May 13, 2003

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It's a new suit isn't it Matt? And IIRC you're more used to fresh water than sea dives? Was your previous suit a membrane or neoprene (or even a semidry?)

If it helps, I found that going to a membrane from a neoprene meant a bit of a learning curve (again) with buoyancy, I also found that I needed more air in my membrane than neo and that filling and dumping were slower with a membrane.

As far as the amount of weight, I've always found it's a bit tricky simply comparing how much various people carry, I've had loads of problems in the Uni club with trainees talking to experienced divers, usually carrying twinsets, and then they turn up at the dive site with six pounds of lead

Or they get ok buoyancy, then it goes to pot because they've changed what they're wearing under their suit, even a moderate fleecy will have a detectable effect on buoyancy.

I doesn't matter as much if you feel heavy at the start of the dive, you've got your BCD and suit to compensate, as long as you can do slow controlled ascents when your tank is down to 50 (or even less!) bar.

These days I look at buoyancy (and the lead I carry) more as an art-form than a science, and every time I change some bit of kit it's another learning curve. In all honesty, I'm still looking for that "perfect" setup, but then again I'm a pedantic old git.

I'd recommend doing a bunch of shallow shore dives, getting your tank low on air and seeing how much you need to add or lose, try inverting yourself then righting yourself to see if there's any migration of air, basically just playing around which I often find is one of the best bits of diving

Chee-az
Steve

MATTBIN · May 13, 2003

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Steve
its a membrane and before that all my dives were in a semi, both sea and fresh. My dive totals are about the same for fresh and sea but only 2 sea dives in the bag. I think I have the same 'problem' in fresh as well so I dont think the change of environment was the problem. I added 2kg to my fresh weight. Like you I dont think that because A carries X then B will carry the same, its all so variable. I'm happy that I was a bit overweighted, rather than bobbing about on the surface all the time. But I do feel that my end weight on the smb could do with refining a tad.

Just have to muck about a bit I suppose.

Cheers.
Matt

abucksdiver · May 13, 2003

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Matt,
I'd make sure that you log the weight that you carry on each dive, together with a few notes about how it felt... such as, did you feel too heavy? Too light? Did you have problems holding your safety stops? Kept adding air to your suit/BCD to get your bouyancy right?

I find this info useful when I need to work out what weight I'll use for a particular dive.

I also find that if I've not dived for a while, I need an extra kg, but after a couple of dives, I can remove it again, and maybe a bit more as well.

abucksdiver

Dr Stevil · May 13, 2003

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[b said:
Quote[/b] (abucksdiver @ May 13 2003,12:45)]I also find that if I've not dived for a while, I need an extra kg

Yeah, I know what you mean, you do some diving just before Xmas, then after New Year you somehow need more lead on yer belt, weird innit

I'd add to Abucks comments, record what layers you're wearing under your drybag and undersuit, I tend to use the same thermals/undersuit combo etc to get consistency
Chee-az
Steve

And · May 13, 2003

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Hi Matt

It sounds like you emptied all the air from your suit before the ascent, and then cos you were vertical were then dumping air as you hung onto the SMB. You would have been negatively buoyant anyway doing that. Instead of dumping immediately rise a little first, then dump but only enough to stay neutral and then do that a little at a time. A tip for your stops is to stop at 12, 9 and 6 mtrs and then make sure you take at least 1 minutes to get from 6 to surface, pref 2 minutes. It just takes time mate, you'll get it, and its easier to use your BC for buoyancy instead of your suit, less air moving about.

The only way you'll check your weighting is at the end of your day at Stoney or whatever and drain your cylinder to 35 bar. Depending on your weight system drop to 3 mtr and hold a stop. Don't use your suit for buoyancy, use you bc. If you need air in your bc then you're too heavy. Take a little off until you have no air in your BC and only a tiny bit in your suit to simulate what it would be like at the end of a 20 mtr dive. Thats your weighting. Add 2kg or so for the sea unless you can find a still, shallow piece of sea to play in.

Hope that helps

WL

Mark Chase · May 13, 2003

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Wise words above me thinks.

I changed from a Thinsulate to a Weezel and my boyency went to pot. I found the Weezle a bit floaty so down to the sea shore I went. Then I went for a 5mm Neopreen suit and had to start all over again.

The only way to check boyency IMHO is in the sea your intending to dive and with less than 50bar in your tank. As an example in the UK I dive twin faber 12's and 4 KG in red sea I dive twin 12's and 6 kg. This is due to the fact the read sea is more salty and therefore more floaty than the Channel

As above, I found that new kit new diving environments called for a bit of comfort weight

I dont care who slags me I want to stay down for that stop / safety stop.

I used to be a bit anal about geting my weight down to a bear minimum but these days and especialy on wreck dives where there is not a lot of finning involved I dont worrey so much. I am more interested in balance and trim. Being badly ballanced during a dive is far more stressfull than being overweight IMHO.

When I have a twin set and standarg rig I use 4kg. I keep that weight for all dives using a twin set so when I go in with two 7ltr stages I am well over weight. I have to put a shead load of air in the wing on the surface to stay afloat at the begining of the dive and releasing all said air has me plumiting to the bottom like a brick. I hit 50m on Friday in just over 70 seconds

It sounds awfull but if I ever go tit's up technical on a dive I could end up with empty back gas and empty stages all of which float. It is likley in that situation I would be holding my 6m stop for as long as gas will allow and I damed well want to make sure thats possable.

All the Best

Mark Chase

Dr Stevil · May 13, 2003

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[b said:
Quote[/b] (Mark Chase @ May 13 2003,14:46)]As above, I found that new kit new diving environments called for a bit of comfort weight

I dont care who slags me I want to stay down for that stop / safety stop.

A sound idea Mark, similarly I always were a little extra when I'm instructing to cope if/when trainees lose their buoyancy control. 50m in 70 seconds - blimey!, on air? bet that gave you a bit of a head spin or did you have trimix?
Chee-az
steve

Mark Chase · May 13, 2003

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No way Air on a UK 50m dive M8. 23/20 for me on that one.

When you have only 30min bottom time it pays to hit the wreck ASAP

Mark Chase

Mdemon · May 13, 2003

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Yup, I think WetLettuce has covered it well. I would add that I'm always surprised how much air is in my DS before I dive - I often have to duck-dive to get down. However, I am generally about 2Kg over-weighted (I subscribe to the Mark Chase school of thought on this one) when I do the test at the end of a dive, with both tanks on 50. I guess a lot of people would add more weight on the next dive having remembered the problems getting down in a similar situation, when this might just be the residual gas before it is squeezed out by pressure. In other words, the end result is more important.

Dr Stevil · May 14, 2003

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[b said:
Quote[/b] (Mdemon @ May 13 2003,21:24)]Yup, I think WetLettuce has covered it well. I would add that I'm always surprised how much air is in my DS before I dive - I often have to duck-dive to get down.

Easy solution to that one, once your DS is on, squat down with the dump valve open (or pull the neck seal out a bit) and all the air will squeeze out, voila ! you'll be "vacuum packed", doesn't feel good but makes life easer than duck diving

Chee-az
Steve

MATTBIN · May 15, 2003

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Thanks all, and those that replied on Handbag that are on here too.

Certainly a few things to check/revise.

Matt

Mdemon · May 15, 2003

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Er, Steve, the air I'm talking about is what's left AFTER vacuum-packing. But thanks anyway.

John Gulliver · May 15, 2003

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[b said:
Quote[/b] (Mdemon @ May 15 2003,10:25)]The air I'm talking about is what's left AFTER vacuum-packing.

Qué? Why is there air left in your suit? How can there be if you're "vacuum-packed"? If your autodump is fully open at the beginning of the descent and you raise your shoulder slightly so that the valve is the highest point in your suit, so that you're suit squeezes on the surface, there should be no air left in your suit. Am I missing something in your reasoning?

Mark Chase · May 15, 2003

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Air in dry suits well I surpose it depends on location of the dump valve, baggyness of the suit.

My problem is often air in the wing. My wing dosent deflate fulley at the surface unless you kind of flip back on to your back. I am often seen doing contortions trying to get air out of my wing at the surface.

Role to the right then lean back is the usual requirement if I am on twin set thats half full for the second dive.

Dont have a problem with the dry bag thow due to the fact it's neopreen. I dont even have to do the pre dive squat.

ATB

Mark Chase

Overweighted?

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