Struggling to understand buoyancy and trim wearing my gear

[seaway2121]

Pushing water is heavy enough why wear yourself out more pushing heavy fins as well

Are my 7mm boots causing too much lift though? How can I compensate for that otherwise?

 

[seaway2121]

Quite the puzzle! Is this a fast or slow rotation?

I would suggest trying the AL tank again, now that you know a little more about what's involved. That tank should have required about 4 more lbs than the steel (more weight on the waist), so perhaps that aspect was overlooked. The other cheap option to try is a weight belt instead of integrated weights, as it will typically ride lower.

Definitely adding another cam band to the lower end of the tank to hold weights will help. That's a long lever arm and you could easily shift 10-12 lbs to there which I'd guess would substantially over correct.

Negatively buoyant fins would help (XL Hollis F1 is -1.5 lb combined). Fins are not terribly negative, but the lever arm is also long. Try to borrow for a test so you're not out $$ if it doesn't work.

The rotation is pretty slow (5 seconds to go from horizontal to vertical), but speeds up as I approach vertical. I will practice next weekend some weight distribution.

 

[inquis]

The rotation is pretty slow (5 seconds to go from horizontal to vertical)

You may be pretty close, then. Something like heavier fins or less buoyant boots might do the trick. Good luck on the next attempt!

 

[AfterDark]

Are my 7mm boots causing too much lift though? How can I compensate for that otherwise?

Those 7mm boots maybe your issue. I use 5mm boots here in RI and I'll still roll head 1st if I place my tank too high on my back. Get a couple of 16oz fishing sinkers and tuck one into each of your boots. At least you'll find out if it's the boots/fins or not. If your weights are not distributed correctly you'll still roll if the boots/fins are not your issue.

 

[jadairiii]

First off, switch to a SS back plate, that will put 6 lbs (or more) evenly distributed on your back. Second would be to start off laying on the bottom, in the proper "horizonal position". Then, slooooowly inflate your wing, little at a time until you are just off the bottom and dont move. if you start to shift, drop back down and start again. While doing this move your head up and down, to see how it effects your trim, do the same with your feet/legs (dont do it at the same time). This will teach you the nuance of adjusting trim. and another thing, focus on steady breathing, when learning proper trim, often, as the student starts going out of trim, they increase their breathing, lungs fill, and that totally screws the pooch. Fill those lungs and vertical you go!

Often times a student will start to over compensate for a buoyancy shift that really just requires a slight adjustment of your feet or head.

 

[NorCalDM]

You also mentioned you started with an Aluminum cylinder, if it was a standard aluminum cylinder it will be lite in the bottom. So raise the cylinder to raise your head and lower it to lower your head this is opposite of a steel cylinder or an aluminum neutral. Make small changes and see how they affect you if you change too many things at once you won't know what worked and what didn't or it gets you going too far in the wrong direction. You started with everything new so you have too weed out what works and what doesn't. I agree with what jadairiii said about getting a steel plate for that thick of a wetsuit. I use a steel plate with my 8mm suit and an aluminum with my 3mm and 5mm suits.

 

[johndiver999]

I always had the opposite problem with a 2 piece 7 mm suit. Had to add lead to front of bc and or ankle weights around the tank valve to be comfortable. It is hard to image how someone wearing 2 layers of 7 mm neoprene over torso and presumably a thick hood is going nose down.

But if I were in that situation I would put a 3 lb weigh on a cam band or even duct tape it to the lowest spot on the tank I could manage and see how that works in a benign environment.

 

[wnissen]

I'm pretty thin. 140lbs. I tried weight testing just the shorty 7-mm, and that was about 14 lbs to be neutral I think.

But I really need to do the proper weight check myself as you said. Definitely should have done this before the course.

Everyone has a different body composition, so it's certainly possible you do need that much. What water temperature are you targeting? My 8/7mm is for colder water, up to 65F / 18C, and even for 55F/12C I only wear 5mm boots. So switching to a 5mm suit and boots might stabilize you some. And of course checking for the aluminum/steel tank difference. An aluminum 80 is by far the most common tank you'll see, except in cold water regions, and it looks very similar to a steel high-pressure 100, which is only two inches shorter. A steel 80 is 6 inches shorter than an aluminum 80, and looks notably squat and small, to my eye. I think it would be hard to confuse them. (All have the same diameter.) But in any case they have very different buoyancy characteristics.

 

[Centrals]

All very good suggestions.

Booties(definitely) too positive, fins(may be) also, tank too high.
SS plate should help. Transfer some of the dead weight to the cam bands.

Keeping trying and you will fix the issue eventually.

 

[MichaelMc]

First off, switch to a SS back plate, that will put 6 lbs (or more) evenly distributed on your back

SS plate should help. Transfer some of the dead weight to the cam bands.

They are head heavy with AL plate and all their lead in hip pockets. So switching to a steel plate will move some of their adjustable ballast higher not lower. Making things worse.

The center of mass of that plate (and the cam bands) is higher than the center of mass of the lead on their hips. It is grade-school playground see-saw physics.