Weighting question

[Nwbrewer]

thinking that maybe she wasn't letting go of the air in her lungs as well as she should have

Bingo!

[ljjames]

Strange to me that it happened to both of you... therefor I'll go out on a bit of a stalk of kelp.

IT could be (and this is a bit of a zebra) that the tide changed and was now pushing back the river, so on the first dive you had more fresh water on the surface (do you remember any visibility change, a temperature change and/or pearly water in the top 4'?) and therefor gained just enough negative to slip past that "noob with gas in suit or trapped in BC" stage on the first dive but didn't have that benefit on the second dive...

Only one problem with that thought Laura...we were in Cove 2, there wasn't any fresh water river to push back in with the tide change.

As for your funkie dance...Danee and I would like to see that...hehehe

Duwamish river....

[CaptnJack]

There is a freshwater lens on top of parts of puget sound and hood canal seasonally. Depth depends on time of year (rainy vs dry season) and recent winds. Not so much the tidal exchange. In winter we can get up to 6-8ft of fresh water in places. In summer its typically pretty minimal (few inches).

[LowDrag]

Strange to me that it happened to both of you... therefor I'll go out on a bit of a stalk of kelp.

IT could be (and this is a bit of a zebra) that the tide changed and was now pushing back the river, so on the first dive you had more fresh water on the surface (do you remember any visibility change, a temperature change and/or pearly water in the top 4'?) and therefor gained just enough negative to slip past that "noob with gas in suit or trapped in BC" stage on the first dive but didn't have that benefit on the second dive...

Only one problem with that thought Laura...we were in Cove 2, there wasn't any fresh water river to push back in with the tide change.

As for your funkie dance...Danee and I would like to see that...hehehe

Duwamish river....

Ooooops...my bad. Had no idea there was a river nearby. Sorry about that.

[Mortuus]

Doh! Yeah, that might do it. I was free diving in Cove 2 a couple months ago and was using 4 lbs of lead at high tide. I went out there another day (low tide) only to find that 4 lbs was sinking me on the surface. It wasn't a small change in buoyancy either. The swing was quite drastic. So that may have been the issue if the tide was higher on the second dive

[LowDrag]

Doh! Yeah, that might do it. I was free diving in Cove 2 a couple months ago and was using 4 lbs of lead at high tide. I went out there another day (low tide) only to find that 4 lbs was sinking me on the surface. It wasn't a small change in buoyancy either. The swing was quite drastic. So that may have been the issue if the tide was higher on the second dive

I would have to check the tide schedule but I believe the tide was low at the time of the second dive.

[DFessler]

#1: Catalina S80 3AL3000 TC -3ALM207 DOT-3AL3000 AS0336533 M4002 03C03 - weight at 500 PSI = 35.6 lbs

#2: Catalina S80 3AL3000 TC -3ALM207 DOT-3AL3000 AS0368361 M4002 03C03 - weight at 500 PSI = 35.6 lbs

#3: CTC DOT -3AL3000 S80 M4002 A45413 - weight @ 500 psi = 38.6 LBS

#4: CTC DOT -3AL3000 S80 M4002 A45460 - weight @ 500 psi = 38.6 LBS

Is there a chance you both dove tanks 3 and 4 on the first dive then 1 and 2 on the second. By your chart above there is a 3 lb difference in the tanks.

[LowDrag]

Yep...that is exactly what we did but I figured after getting home and weighing them that the second set of tanks being full would negate that three pound difference. I had no idea at Cove 2 that there was a weight difference between the first and second set. Do you think it would make a difference even with full tanks?

[Jeff Pack]

the weight of air is constant. so even full one set will weight +3 over the other set (both being full).

[Desert Diver]

But remember that what the tanks weigh out of the water is only meaningful if the tanks displace an identical amount of water

[LowDrag]

Interesting...I would have thought that a tank weighing in 3 lbs lighter @ 3000 PSI would still out weigh a 3 lb heavier tank that was only @ 1000 PSI. I take it this is not the case?

I got the video from this dive up on YouTube last night if anyone wants to see it. It is a bit long @ 11 or so minutes (I suck at making them 5 minutes long). This weekend we are taking the same tanks back to get this weight thing down and look for the GPO that is under the Honey Bear wreck.

http://www.youtube.com/watch?v=FIehedPc ... e=youtu.be

[Desert Diver]

The amount the tank floats or sinks is equal to the weight of water it displaces minus the total weight of the tank, valve and air. On the charts you will see that the numbers for full to empty buoyancy appear to be incorrect but full tanks stretch and displace a little more water.

[mpenders]

This weekend we are taking the same tanks back to get this weight thing down and look for the GPO that is under the Honey Bear wreck.

Suggestion: If you end up with same tanks (2 of one kind, 2 of another), plan on each of you using the same type of tank on both dives. That way, you don't (shouldn't) have to work out weighting for the 2nd dive - just switch out tanks and go dive.

Ultimately, the dry weight of your tanks (full or empty) is not the number you need to be paying attention to when determining your weighting requirements. The buoyancy characteristics are much more important. A difference in dry weight between tanks does not equal the same change in buoyancy.

Once you have your weighting figured out, you should only need to adjust your lead requirements based on the buoyancy-when-empty (500psi) specification of the tank you are using.

[Desert Diver]

Yes, that's what i meant!

[LowDrag]

Very good point, we will try that on Saturday. One other question about weighting. When you do your 500 PSI buoyancy check (at the end of your dive) you shouldn't have to add more for the beginning of the next dive? The weight at the 500 PSI check should be enough because the tank will be heavier at the beginning of the next dive correct? Regardless of whether I am diving AL80's or Steel 100's?


I checked the spec's on the Catalina S80 and the chart says that these tanks are -1.6 Full, 2.8 @ 500 PSI, and 4.1 empty.

[Desert Diver]

So long as your next tank is identical.

[LowDrag]

So long as your next tank is identical.

Exactly...I just forgot to say that. Thanks

[LowDrag]

We think we found the glitch. On the first dive she forgot to put on her weight belt on so I put it on her in the water when she was in just above her waist . On the second dive she did NOT forget her weight belt, probably trapping air in her suit and she could not get down. So that would fit with what some of you said about trapped air hiding in her suit. For the last two dives we have done...one at Cove 2 and one at Timothy Lake...she put all of her weight in her BC and has had zero issues with getting under water.

Thanks again for everyone's help with this question, I really appreciate it.

Thanks,
Dave