Semidry wetsuit for warmer water?

[DaleC]

Ok, I don't know much about the magical qualities of Mexican cave water but I want to know more about these buoyancy numbers.

I dive a worn out 3/2mm wetsuit vintage (no BC) and need to add 4-5lb's lead to be just a tad positive at the end of a dive with one Al80. For a Steel 72 I wear 3lb's. In my 7/5 Pinnacle semidry I wear 18lb's to freedive (just did that two weekends ago) and about 21/22 lb's with a single St72 (just did that yesterday). If I wanted to fine tune it could probably drop 2lb's but suit compression at depth does occur and you can't get down or hold stops if you weight for depth only.

How does one wear 4-6lb's in a 7mm with twin 80's? Just the gas expended equals that so you are saying you are neutral with a 7mm? I wanna know because I will buy that suit and my friend owns a Neotek so I know it isn't that one.

 

[Adobo]

Ok, I don't know much about the magical qualities of Mexican cave water but I want to know more about these buoyancy numbers.

I dive a worn out 3/2mm wetsuit vintage (no BC) and need to add 4-5lb's lead to be just a tad positive at the end of a dive with one Al80. For a Steel 72 I wear 3lb's. In my 7/5 Pinnacle semidry I wear 18lb's to freedive (just did that two weekends ago) and about 21/22 lb's with a single St72 (just did that yesterday). If I wanted to fine tune it could probably drop 2lb's but suit compression at depth does occur and you can't get down or hold stops if you weight for depth only.

How does one wear 4-6lb's in a 7mm with twin 80's? Just the gas expended equals that so you are saying you are neutral with a 7mm? I wanna know because I will buy that suit and my friend owns a Neotek so I know it isn't that one.

Mostly fresh water (there is a halocline though) which means that you need less ballast to start out with. Also, anyone diving doubles is likely using a backplate. A canister light and two backup lights. Finally, for doubles, you have to factor in the manifold plus the extra first stage.

It's been a few years since I've been in Mexico but if I remember correctly, I only used a 4lbs weight (partial v-weight) along with my steel backplate while wearing a drysuit and a thin undergarment. That seemed like it was enough for diving with double al80s.

 

[DaleC]

I dive freshwater too and those are my numbers.

Now, if those people are using BP's, canisters etc... and not counting them as weight then I can see where they are coming from - but that's a little deceptively harsh against T bone's numbers. A back plate can be 2-4lb's, a canister, depending on brand can be another 4.. so that makes 4-8lb's + another 6-8lb's which equals about 10-16lb's of weight. That sounds more reasonable to me. My semidry at 18lb's is pretty buoyant with merino wool lining and takes along time to fully saturate.

Some divers up here dive double core 7mm wetsuits in the winter and often wear upwards of 30lb's of lead.

 

[gearhound]

Dale, we're not talking about double core 7mm. Haloclines are not much of a worry. Depending on how far inland you are, they are at depth. You'll lose compression in your wetsuit.

And I'm not going to dispute the numbers that you need to sink because everyone is different. I do not need lead to sink in a 3mm. I have a size ML Neotek. Even when it was new, I only required 10lbs to sink in it. It has been to depth a few times since, and requires less now.

Okay, I'll be that guy -
I love this video from our last trip https://vimeo.com/130268298 You'll see 3 of us with Neoteks on, 2 with other 7mm wetsuits, and the rest with 5mm wetsuits. Dives ranged in depth down to 130' at the Pit and Zapote. The most anyone had on for weight was 8 pounds I believe. 5mm divers did not need any weight. Double stage dives, but no deco dives on this trip. No issues holding our stops, but nobody blew through their thirds.

If you look at 2:20 of this video https://www.youtube.com/watch?v=3eJhInfPGXk I'm going through a restriction where I had to take drop both tanks in to pass the restriction before attaching them and starting the dive. So I'm not counting the tanks as ballast. Neotek, 4 pounds of lead, no issues.

 

[DaleC]

Nice video.

I don't get how anyone could dive a 5mm with no lead, unless the weight is made up in the rig. I'm not being argumentative, I just don't see it. Not with Al80's anyway. But life is full of surprises. I'm gonna borrow my buddies neotek and see what I can get away with.

 

[boulderjohn]

how much weight do you need to wear with a 7mm wetsuit and 2 al80's? You need at least 8 for the tanks, and the average 7mm wetsuit is between 15-25lbs positive at the surface *semidry's usually more*, so at best you're 25lbs, likely closer to 30lbs. So that's 25-30lbs of lead you have to carry on land to sink you plus the tanks for fresh water. If he's doing salty stuff it will be even more. Over half of which has to be switched to the wing at depth due to compression. 3mm or drysuit doesn't have the buoyancy swing, thus better/smarter/safer for deep diving, combined with better comfort. You still haven't given a reason why you think a thick wetsuit/semidry is better than a heater or a drysuit other than "because you've done it"

I would like to add my own experiences to those who have already challenged this. When I dive in the caves in Mexico, I use a 5mm suit (Henderson) that some call a semi-dry. I use no weight at all with double aluminum tanks. When I dived caves in the Bahamas, I went warmer with a 7mm suit and was a bit heavier than I would like to be with the LP 85s I used, also carrying no additional lead. In both cases, though, I was using a steel BP. I certainly don't need 25-30 pounds.

I recently did the OW certification dives for a student I had not had in the pool. He had used a 7mm suit in the pool to make sure he knew what he would need during the OW dives, and he was convinced he needed 22 pounds with a single AL 80 and a standard jacket BCD. I got him down to 10 pounds of lead, and he was a much happier diver

 

[DaleC]

John, did you have a can light and, if so, how much weight does that represent? Curious.

 

[boulderjohn]

how much weight do you need to wear with a 7mm wetsuit and 2 al80's? You need at least 8 for the tanks, and the average 7mm wetsuit is between 15-25lbs positive at the surface *semidry's usually more*, so at best you're 25lbs, likely closer to 30lbs. So that's 25-30lbs of lead you have to carry on land to sink you plus the tanks for fresh water. If he's doing salty stuff it will be even more. Over half of which has to be switched to the wing at depth due to compression. 3mm or drysuit doesn't have the buoyancy swing, thus better/smarter/safer for deep diving, combined with better comfort. You still haven't given a reason why you think a thick wetsuit/semidry is better than a heater or a drysuit other than "because you've done it"

John, did you have a can light and, if so, how much weight does that represent? Curious.

I did--a fairly heavy Hollis 25 watt. That is still not going to add all that much weight.

 

[Adobo]

Nice video.

I don't get how anyone could dive a 5mm with no lead, unless the weight is made up in the rig. I'm not being argumentative, I just don't see it. Not with Al80's anyway. But life is full of surprises. I'm gonna borrow my buddies neotek and see what I can get away with.

I was in Maui recently. I dove an aluminum plate with 6 lbs of ballast while wearing a 5 mil suit that is slightly too big for me. The suit only has maybe 10 dives on it and has never seen deeper than 80 ft. And I think I was slightly overweighted. If I was wearing a steel plate, I could have probably gotten away with 0-2 lbs of ballast. And that is in salt water.

Going from single al80 to a double al80s, I am not sure that any buoyancy is gained by adding the second tank. The reason is, when you have doubles, you add a manifold, bands and a second regulator.

I can totally see how someone with a 5mil suit could dive double al80s without much additional ballast outside of an aluminum plate, maybe some jetfins and a canister light.

 

[boulderjohn]

How does one wear 4-6lb's in a 7mm with twin 80's? Just the gas expended equals that so you are saying you are neutral with a 7mm? I wanna know because I will buy that suit and my friend owns a Neotek so I know it isn't that one.

I missed this earlier, and I will try to reply to what I understand you to be asking.

When doing any kind of technical diving, including cave diving, a lot of gas is used, and you therefore bring a lot more gas with you to be safe. At the beginning of the dive, with all the equipment, etc., I am often so overweighted in the classic sense (float eye level holding a normal breath with BCD empty) that I am still a little overweighted at the end of the dive, when my cylinders are getting lower on air. At the end of a cave dive, we are not diving with near empty cylinders. If we are entering into flow and turn on thirds, we will end the dive with tanks half full. If we are entering into a totally no-flow cave, we will end the dive with tanks 1/3 full. We have to weight ourselves, though, for the remote possibility that we will end the dive with tanks nearly empty, so that means that we will end the dives overweighted by at least the weight of gas still in the tanks.