Quiz - Skills & Environment - Overweighted Diver

[johndiver999]

johndiver999,

I found an article from 2009 with the inherent buoyancy of a bunch of different 3 mm models.

The actual thickness and inherent buoyancy of any particular wetsuit is immaterial to my point.

Whatever the thickness of the suit--I don't care if it's 15 mm thick and has 10 kg of inherent buoyancy--if you start your dive positively buoyant and swim down until you reach a depth at which the compression of your suit makes you neutral, that will be the moment at which the race begins between a tank that grows increasingly positively buoyant and a suit whose rate buoyancy loss will be diminishing.

In fact, if you have an extremely thick suit, you will be so deep when you hit that neutral moment that your air consumption will be highly accelerated and your remaining wetsuit compression will be down to 15 or 20 percent of its potential at the surface. The rates won't be equal and won't offset.

You will still be exactly correctly weighted at only one moment, which is what this sidebar is about.

Thanks for the suit buoyancy reference. I think their information is inconsistent with my experience.

At the start of a dive, and with a thick wetsuit, the LAST thing anyone would want to do is start buoyant and then swim down - (assuming their BC is empty).

Also, with a thick suit, the buoyancy swing is larger/faster compared to a thin suit. For example, a diver wearing a thin wetsuit, could conceivably swim straight down from the surface to 100 feet and add zero air to the BC. The diver might use the moderate amount of decreased buoyancy to aid/speed their descent. Upon reaching their target depth, they THEN might add air to the BC to establish neutral condition.

Conversely, a diver doing the same thing with a full 7 mm wetsuit, would become very negative and this might induce an excessive descent rate and might even result in an out of control situation where ear equalization might lag descent rate and this could cause an injury.

So I am unsure why you think a diver would need to go deep with a thick suit to see a material swing in buoyancy, in fact, I think the opposite is probably true. With a thick suit the diver probably wants to be on top of suit compression and add some air to BC during the descent - early and often.

 

[Ripley]

We all know that some (many? most?) instructors deliberately overweight their open water students, believing that doing so is the best way to anchor them in one spot long enough to demonstrate skills.

True. And it's a great help to master the dust kick
Additional advantage: you get to master the inflate/deflate function of the BCD in a very short time.

 

[wetb4igetinthewater]

But..but... it looks so cool! Even cooler is reversing it with the strap on the forehead and mask at the backside.
The aquatic version of the reversed baseball cap.

j/k.
It amazes me to see how many divers actually put their mask on the forehead / back of the head.
Did it once during one of the pool trainings. Once! Mentor waved his hand towards me (I thought by accident) and down went the mask. "Go and get it..." Then I knew it wasn't an accident but on purpose. Lesson learned.

 

[Pedro Burrito]

Spoiler: Answer

c. move less efficiently through the water because more air must be added to the BCD to compensate for the extra weight.

 

[TMHeimer]

But..but... it looks so cool! Even cooler is reversing it with the strap on the forehead and mask at the backside.
The aquatic version of the reversed baseball cap.

j/k.
It amazes me to see how many divers actually put their mask on the forehead / back of the head.
Did it once during one of the pool trainings. Once! Mentor waved his hand towards me (I thought by accident) and down went the mask. "Go and get it..." Then I knew it wasn't an accident but on purpose. Lesson learned.

Yeah. The non MOF folks don't realize that you have better peripheral and overall vision with MOF when walking on seaweed covered rocks on land at the shore or even in 1 foot of water. It won't be lost and it's safer.

 

[TMHeimer]

The best SB smile came last year when someone asked how they could carry 53 pounds of lead because they were diving a dry suit. LMAO!!

I wear 42 pounds with my 7 mil farmer john. I should maybe know this, but what amount of lead would that probably translate to if I wore a drysuit? Is 53 pounds way over? I honestly have no idea about drysuits except that I know you need more weight. All of our students used farmer johns , so there was no need for me to know about drysuits.

 

[Scuba-74]

I wear 42 pounds with my 7 mil farmer john. I should maybe know this, but what amount of lead would that probably translate to if I wore a drysuit? Is 53 pounds way over? I honestly have no idea about drysuits except that I know you need more weight. All of our students used farmer johns , so there was no need for me to know about drysuits.

42lb is a scary number...

EDIT: there is no way of telling if that's too much w/o knowing all the specifics, but it does seem like too much. How much you add with a drysuit depends on the undergarments and they way your drysuit fits, in my experience it's roughly 10-12 pounds added to you 7mm wetsuit weight. I tend to wear 14-16lb with 7mm, and 26-28 with a drysuit, when diving HP100 tanks.

 

[Scraps]

But..but... it looks so cool! Even cooler is reversing it with the strap on the forehead and mask at the backside.
The aquatic version of the reversed baseball cap.

j/k.
It amazes me to see how many divers actually put their mask on the forehead / back of the head.
Did it once during one of the pool trainings. Once! Mentor waved his hand towards me (I thought by accident) and down went the mask. "Go and get it..." Then I knew it wasn't an accident but on purpose. Lesson learned.

As a sea service veteran, I consider wearing a mask to be akin to our tradition of "being covered" (i.e., wearing headgear) any time we are outdoors in uniform or under arms indoors.

This analogy avoids the question of where to put one's mask by encouraging divers to wear their masks for the entire duration of their dives--from splash to feet dry. If it's uncomfortable, find a mask that fits or learn to adjust the one you have. If it's fogging up, learn to clean and treat it properly. If you need to take it off to rinse it or to re-apply de-fogger, keep it in your hands until you've done so and then put it back on your face.

Since divers already plan to to wear their masks for hour-long dives, it shouldn't be a hardship and it quickly becomes a good habit to keep them on their faces for those few extra minutes between the time they surface and the time they climb out of the water.

I'm not totally hard-core on the subject. If it's a training dive at an inland dive site where it's always FAC and you're conducting a de-brief while gently kicking back to shore, I have no problem with removing one's mask. But if there's any chance I might need my mask again, I try to leave it in place.

With the exception of fins, which can impede getting out of the water, I don't think there is any other gear we routinely doff while in the water for no particular reason.

 

[TMHeimer]

42lb is a scary number...

EDIT: there is no way of telling if that's too much w/o knowing all the specifics, but it does seem like too much. How much you add with a drysuit depends on the undergarments and they way your drysuit fits, in my experience it's roughly 10-12 pounds added to you 7mm wetsuit weight. I tend to wear 14-16lb with 7mm, and 26-28 with a drysuit, when diving HP100 tanks.

Yeah, but I know of a couple of instructors here who wear in that area with the farmer john. I did get it down to 37 over 10 years with my old wetsuit losing "integrity" (I assume), but with the new one back to my original 42. It is what it is. With 37 I can completely deflate the BC and exhale and not begin to descend. So, that being said, 53 pounds would be about right for me if I got a drysuit. Huh.
Is your 7mm wetsuit a farmer john?

 

[Scuba-74]

Yeah, but I know of a couple of instructors here who wear in that area with the farmer john. I did get it down to 37 over 10 years with my old wetsuit losing "integrity" (I assume), but with the new one back to my original 42. It is what it is. With 37 I can completely deflate the BC and exhale and not begin to descend. So, that being said, 53 pounds would be about right for me if I got a drysuit. Huh.
Is your 7mm wetsuit a farmer john?

Actually, mine is not a farmer john, so probably you need to add less than 10lb. Also, it’s getting old, and more compressed.

Good point, I’d probably have to wear more weight if I had a farmer john, especially newish.