Too Many Gear Changes for One Dive?

[USMCMcG]

I think I know the answer to this, but would like to hear your collective thoughts.

I am a new diver certified 3 months ago. I am 5'9" and a voluptuous 230#. Nomal gear is a 3mm long wetsuit with AL80 and a Mares Hybrid BCD. I get pretty close to neutral bouyancy with 14#. I've recently bought some new gear and have been trying it out.

Last Wednesday changed to a Henderson dive skin and dropped 2#s to 12 total. Pretty close to neutral. SAC at 55' average depth was .563 and .607 on two dives.

Yesterday changed to steel 100s AND changed from lighter Mares fins to Apollo Bio Fins. Dropped 4# to 8 total and felt overweighted. Definitely had to add more BC air at the bottom. Again averaged 55' on two dives but SAC went up to .816 and .773 over two dives. I also had a big juicy burger and fries the night before (in case that makes a difference).

The only other difference was the Wednesday dives were in the morning and the Sunday dives were afternoon.

I plan to dive again with the Mares fins and steel 100s to see if it was the heavy arsed Bio fins that made my SAC go up so far. Not sure about the burger this time though.

Does the collective "you" think the fins made that much difference or should I have dropped more weight to compensate for the steel tanks?

 

[Kitty_Kat]

When I go from one of my aluminum 80's to a HP steel 100 I usually drop ~8 lbs keeping all other parts of my configuration the same. The amount that you could drop may be slightly different depending on the specific specs of the tanks you are using, but probably should be more than 4 lbs...

I have never noticed a huge difference with fins... I regularly switch between a pair of Jet Fins and a pair of Seawing Novas. Two very opposite ends of the weight/buoyancy spectrum, but the change has never noticeably affected my SAC or weighting.

 

[boat sju]

New/different gear can be stressful. I try not to change more than one thing at a time and then get used to it for a bit before changing something else. Even simple stuff like a mask or fins.

Besides changing your weighting you affected your trim too - you were probably more uncomfortable/stressed than you realized.

 

[mruseless]

First off, regarding proper weighting: At the end of your dive, after you have completed all your required and recommended safety stops, purge your tank down to about 300-500 psi. See if you can hold a stop at about 10' with no air in your BC and without kicking. If you can do this, without finning, you are properly weighted. If you have to fin, or put air in your BC, try dropping a couple pounds of lead and try it again. You can do this on the next dive, or on the same dive if you can hand off one or two pounds to your buddy safely. Obviously if you cork then you are too light (try not to cork, the last 10 feet are the biggest pressure change).

Regarding a configuration change, assuming you are weighted properly I would say you should dive it at least 10 times before changing it again. It takes a bunch of dives to really get the feel for how a given setup will affect balance, trim, buoyancy, etc.

 

[Bob DBF]

I will sometimes change several things at a time, but I never expect things to go well, based on years of experience.

As mruseless advised, do a weight check at the end of each dive, then log the results so you can dive that configuration again and see how it works out with the proper weight. Then you can work on trim.

Don't get too focused on your SAC rate until you get your rig sorted out, it will just make you crazy. Anything from stress to buoyancy problems will affect your SAC. Get your rig sorted out and dive it a while and see what happens.


Bob
-------------------------
I may be old, but I'm not dead yet.

 

[Steve_C]

I have done identical dives on two days with identical water conditions. SAC was 20% worse on day 2. Reason was on day 1 I was a follower. On day 2 I was leading a drift dive and I had stragglers and swimmers and kept having to look around to keep track of them. No difference in physical effort. All mental.

 

[fjpatrum]

On my last "training" dive in the quarry I had problems. My write-up can be found here:http://www.scubaboard.com/forums/basic-scuba-discussions/459556-my-first-called-dive.html

Long and short of it, my number one lesson for the dive was "one gear change at a time".

 

[tracydr]

I generally don't make more than one change on an ocean or lake dive. This includes small things like lights and cameras.
If I make several changes, I do a few good pool dives before heading too the ocean. I'm lucky enough that we have a deep pool of our own.

 

[redacted]

I am about your caliber. My XXL 3mm full suit is about 7 lb buoyant. That means, if I switch to a dive skin with everything else the same, I drop 7 lb from my belt. While there is a bit of variance, I expect 5 lb would be the minimum. 2 lb is just not enough. The 4 lb decrease for thye steel 100 is about right. I suspect your problem is that you needed to drop at least another 3 pounds, and maybe 5, when you switched from the 3mm to the skin.

 

[uncfnp]

Sac rates can very a great deal from dive to dive and can be affected by a great many things. Did you feel colder in the skin vs the 3 ml? Was there more current (or less if drift diving)? Did you feel like the finning was different/more effort? Were you stressed about by the new gear? These are just a few of the possibilities for the higher SAC.

As for weighting, I recommend, if not already, keep a log of your different gear configurations with the weighting for each and how it felt. For me, I drop about 6 pounds between AL and Steel.