Thermal Protection, over estimate the need?

[txgoose]

Baseline Story: This weekend we all under estimated our need for thermal protection and it eventually cost us our planned third dive.

Longer version:
In November, we dove a local spring fed quarry. It was cold, but we all wore hoods and the biggest annoyances were the impaired hearing at the surface, and a very noticeable jaw fatigue while talking. The hood wanted your mouth shut!!!

Fast-forward to this past weekend. We were in northwest Arkansas diving in Beaver Lake. Unsure of the exact water temperatures we watched others that were already diving. It seemed like there was a 60/40 split of who was or was not wearing hoods. 60% were. But the above mentioned annoyances caused us to vote with the other 40%. Long story short, by the end of the second dive the bulk of the family was completely wiped out as all of their energy was being used simply to reheat the body.

My takeaways:

• We will now err on the side of wearing more than we think we'll need.
• We need to buy hoods that are comfortable so that we won't be hesitant to use them. Or at least much less hesitant.
• We very simply could have added the hoods for the second dive. We were dorks. Twice.
• We were shallow (avg depth 21ffw and 22ffw for each dive), short dive times (29, 32 minutes), and had good buddy pair attention. I can see how poor thermal management could get incredibly critical for dives that might not appear complex, until the mind starts slowing down and the body begins to protect the core.
• The thermocline was so sever that we could see the density change. That was neat to experience.
• In cycling we start cold because we will warm up. In SCUBA we need to start warm and cool to it.
• Vote with the 60%. Sometimes it is best to follow the crowd.
• When the boat propeller sounds really close and makes you nervous, LOOK UP. No near miss for my family, but the "dive park" had a boat come through multiple dive buoys. Have heard boats before, but this time we could hear the cavitation. It was a bit unnerving.

Nothing to be proud of, but just a post for others to possibly learn from. I am actually a little happy that we've all experienced it early on in our dive careers to learn from it. Because of our good buddy pairings and the short dives, it was probably a good place to learn. BUT, for others that are new to cold/cool water, don't feel like you need to learn it the hard way. Just dress well to begin with.

 

[tbone1004]

what were the actual water temps of what you were used to and what the above and below thermocline temps on this dive were?

 

[txgoose]

Our "summer" lake temps are usually in the 76-78 degree range and we have worn a mix of long sleeve shorties and 3mm fulls. In FL we swam in 82 degrees and board shorts.

This past weekend the water temps were 68/62/57. There were two thermoclines, the main one we dealt with was at 27-28ft. The lower one that we only very briefly crossed was at about 38 ft. It really had a bite to it. Both buddy pairs had the same story about feeling the shock and immediately rising back up out of the lower one. Air temp was 85-90.

 

[tbone1004]

@txgoose I just got teaching for 2 weeks where the surface was mid 60's, bottom was low 50's. We saw instructors and students without hoods out there. To me, I will wear a hood if the temp is below 70 end of discussion, or between 70-80 if exposure is over 30 minutes.
In the temps you described, I would do those dives in a hooded vest with 3mm gloves and booties, before I would do them with a drysuit and no hood.

If you are regularly doing those dives, you guys need to get hoods or potentially hooded vests. The vests can often be more comfortable, especially for surface use. If you don't want to go that route, I would urge you to get drysuit hoods with zippers on the backs of them. It allows a bit more surface comfort and the skirted hoods are good for pretty much nothing IMO

 

[JohnnyC]

You don't want to start warm and cool down. Thermal stress absolutely plays a part in inert gas loading and unloading. You want to start cold and end warm. This becomes much more important on long decompression dives, but you might as well being doing the right thing no matter the dive.

Get a proper fitting hood. It will make a world of difference. And take it off on land or pull it back. Mine stays in my pocket until I'm ready to splash. No point in walking around with it on. If it's too tight to pull back behind your head, it's too tight. It's a wetsuit for your head, same principle applies, you need some room for water to enter and warm up.

 

[txgoose]

I think that we are similar in thought. The 68 was doable. and we probably could have squeezed out the third dive but we would have been just as miserable and of course all of the novelties/sunken stuff was below that thermocline anyway. I can definitely related to your 70 degree delineation.

I don't know that we'll be diving cooler a lot, BUT, I do like the idea of extending our season for as long a possible. Diving in Nov. was neat. Hoods would obviously help. I will look into the dry hoods. And probably a hooded vest. The Ms. has also been working on her weight and she is experiencing new thermal dynamics that she isn't used to simply from that part.

 

[txgoose]

You don't want to start warm and cool down. Thermal stress absolutely plays a part in inert gas loading and unloading. You want to start cold and end warm.

I understand not wanting to be overheated on the shore and/or during the SI. I am not sure how to start a dive cool and end it warm.
Maybe, I should have been more clear. In cycling we start being under dressed for the expected cool temps, because we are fixing to rev the internal engine up and if you start dressed warmly, you'll be over heating or shedding clothes soon. For scuba, when I said start warm and end cool I simply meant that if the water is cold, and assuming warm/summer air temps, I will need to be over dressed for the effort of gearing up. So I will by default start warm. In cool/cold water, outside of electric heaters, I have no idea how to end a dive warmer than I started. At least not while trying to conserve gas.

 

[Marie13]

I always wear at least a 5mm hood and 3mm gloves. Yesterday I was diving the local quarry. Our deepest was 47ft - temp was 45F at that depth. Warmest was 54 at surface. I had on 7mm, Lavacore hooded vest with 5mm Waterproof hood over it, 3mm gloves, 5mm boots (I always wear the same boots).

 

[northernone]

Here's a few thoughts:

My hood goes on 30 seconds before my head goes underwater. Comes off 10 seconds after surfacing (replaced soon after with a winter hat) I dislike hooded vests for that reason.

I don't think I've ever talked in my hood.

I'm a fairly enthusiastic about presoaking my wetsuit with warm water immediately before immersion. Otherwise, the initial loss of heat from warming up ambient water shortens my core temperature "reserves" significantly.

Might something like that increase your comfort? I hate being cold and won't allow it anymore. Half the year I dive in water between 34° and 65°, typically in a wetsuit.

Cameron

 

[tbone1004]

the only way to increase your core warmth at the end of the dive is with active heating. Not really an issue for recreational NDL diving. Neal Pollock has compiled several studies done on the subject

@txgoose the hooded vests are ideal because if it is cold enough to wear a hood, then it is cold enough to warrant an extra 3-5mm on your core. The nice thing is they don't sacrifice flexibility of your limbs which is ideal. The Pinnacles are pretty nice and Cave Adventurers keeps them in stock. They are usually easier to pull back off of your head at the surface than a normal hood. I do not pull my drysuit hoods back, but if at the surface I take them all the way off. Less ideal since you have to take your mask completely off to do that each time as well as keeping track of the hood. If I'm doing a bunch of time at the surface, I'll usually stick my SPG through the hood to keep it contained.
When diving with hoods, you MUST flush the hood on the beginning of your descent. If it is a high quality hood and fits well, it will seal your external ear canal and when you equalize you can blow your ear drum out. Happened to my brother a couple years ago. I usually pull the edge around my face back and rock over to each side until I can feel/hear the water flood my ear canals.