Purging enough air from Drysuit to match previous post dive Buoyancy check

[rfwoodvt]

All gear being the same, it seems that no matter what I do to vent the air from my drysuit I always have to add 2-4 pounds above my last post-dive Buoyancy Check in order to descend.

If I do a second tank dive within an hour or so then I might not need that extra weight, or, if I do, it will be significantly less than on the first tank.

Is this typical for you other drysuit divers as well?

Any tricks of the trade that might help? Or should I just suck it up and plan on that extra weight every time out?

 

[wetb4igetinthewater]

@rfwoodvt

How do you dump air from your drysuit before you get in the water? I would assume that you crouch down to vent.

 

[inquis]

If you are vertical at the surface with the vent at the same setting, you should be squeezed more (i.e., less buoyant) than at your safety stop when you vent the wing. Perhaps an unconscious fuller breath or fin movement is happening? You might try crossing your ankles to make sure.

 

[inquis]

I would assume that you crouch down to vent

I do this but still have a fair bit of air in the suit. There's no way I could descend without letting more out. (I actually like that, as I can stretch out horizontally at the surface to get underlayers situated.) I open the vent to the normal position to start the descent.

 

[Manatee Diver]

I often have to duck dive to start a dive single tank with my drysuit. After a couple of feet I start to slowly sink. I am perfectly weighted for the safety stop.

 

[rfwoodvt]

@rfwoodvt

How do you dump air from your drysuit before you get in the water? I would assume that you crouch down to vent.

That's what i do.

If you are vertical at the surface with the vent at the same setting, you should be squeezed more (i.e., less buoyant) than at your safety stop when you vent the wing. Perhaps an unconscious fuller breath or fin movement is happening? You might try crossing your ankles to make sure.

Though breathing occasionally gets the better of me I'm consciously breathing to avoid just that.
I have tried the ankle crossing trick to no avail.

One thing I have noticed is that when I cross my ankles I tend to tip backwards lol

 

[lexvil]

Boat or shore?

 

[rfwoodvt]

Boat or shore?

Been playing with this mostly with shore dives.

But now that you mention it I recall the few giant stride entries I did from a boat last month seemed to move a lot of air to my shoulders.

 

[lexvil]

Been playing with this mostly with shore dives.

But now that you mention it I recall the few giant stride entries I did from a boat last month seemed to move a lot of air to my shoulders.

For me I swim out with the vent full open on shore dives, this will squeeze out pretty much all of the air. Jumping in from a boat is better if you can get as much air out as possible before you hit the water. Between dives if you stay sealed up the suit tends to shrink fit as it cools. I often add or revove a few pounds for the second dive depending on how everything felt at the end of the first.

 

[inquis]

How do you descend? Are you initially vertical or more horizontal? Do you have an automatic suit vent? Is it set the same as during the previous dive's stop/check?

The only changes from the end of the previous dive (where you were good) is another 5+ lbs of air in your tank but lots of air in suit / wing more than offsetting that. (I'm assuming single tank.)

You must not be venting one or the other to the same degree. If you did, you would be 5 lb negatively buoyant and go right down.

Being vertical (head up) on the surface should easily drive air from your suit through the auto dump valve, though it may take 5 or 10 seconds. If you're going to do it while in horizontal trim, you'll need to roll to raise the vent and is harder to do correctly.