Sea Hunt Buoyancy Control Question

[fisheater]

I just finished (re)watching the bulk of the first Sea Hunt season and I have a gear question.

Without a BC, how did Mike (and his fellow "skindivers") weight himself? It appears that he was positively buoyant at the surface and had to "fight" his way under. Would he go significantly negatively buoyant at depth?

In other words, anyone know how the "oldtimers" handled buoyancy and trim?

Thanks.

 

[drbill]

"Oldtimers" my butt! Weighting was more critical in those days when we either didn't have or couldn't afford BCD's. Much of buoyancy control was based on more precise weighting and use of our lungs (something a number of us still do). I don't remember it being that much of a challenge in the 60's and 70's. I didn't use my first BCD until 1989. Wouldn't dive without one now.

 

[spectrum]

fisheater

Exposure suits were not generally as buoyant as what we have today first of all. That limited the buoyancy change with depth. I have seen it done in a 7mm farmer John but it takes practice and it's a little different that the pinpoint hover anywhere anytime diving many of us strive for.

Remember that at the start of the dive you will be least buoyant with a full cylinder. This lets you get down. Some divers will carry a stone down or a weight that they leave to retrieve for ascent. These dives are well planned with the weight being selected for the dive to be reasonably close to neutral at depth for most of the dive. The rest is managed with a combination of lung volume control (natures own BC) and sometimes some significant swimming. The diver may touch off with a hand from time to time if they stop swimming while so deep as to be very negative. The same laws of physics apply to this sort of dive you are just operating in a narrower band and don't have the fudge factor of a BC bladder.

As the dive progresses the cylinder become less negative and the diver will be lighter in the water. This makes the return to the surface easier as well as the positive buoyancy you see when the diver surfaces.

It's a fun way to dive. I have done it a few times in trunks or a shorty. If you are in minimal neoprene and get the weight just right you are truly free as a bird, able to move up and down the water column just by modifying your lung volume and when you are where you want to be you just keep swimming. You can feel your properties change as you breathe the cylinder down but it's all manageable.

Pete

 

[DA Aquamaster]

I prefer to vintage dive in warm water as with a 3mm shorty or a tee-shirt the bouyancy change is minimal and maintaining neutral bouyacny with lung volume is easy if properly weighted.

With a 7mm wet suit the process is very similar to what a free diver would do. You weight yourself so as to be slightly positive at the surface and neutral at about 15-20 ft.

For a free diver this allows you to rest at the surface when snorkeling but minimizes the effort needed to descend form the surface and minimizes the nbegative bouyancty at depth. (It also ensures that if you suffer shallow water blackout at 20 feet or less that you will float.)

For a scuba diver, the same thing applies. If you are properly weighted at the surface to float at about eye ball level with full lungs and a tank with 500 psi in it, you will sink when you exhale and be neutral at about 15-20 feet with a normal lung volume. This ensures you can still make a safety/deco stop at 15 ft and will be positive on the surface and able to rest whgile breathing through a snorkel. It also minimizes the negative bouyancy at depth and early in the dive with a full tank.

Notice none of the above paragraph mentioned BC-less vintage diving - it works for any diver BC or not and is the proper way to weight yourself as is minimizes your reliance on the BC and mimimizes the air volume in the BC that has to be managed and in turn makes precise bouyancy control much easier.

In the pre-BC era, when diving at deep depths the compression of a thick wet suit and the swing weight of single and even more so double tanks could make for some very physically demanding diving as you had to essentailly swim with a slight upward vector to maintain a neutral position in the water column and you had to power your way up from depth to the point where the wet suit was again more bouyant. No one overweighted themselves as doing so greatly increased the physical demands at depth.

Being fit was vital and the contribution of the BC has largely been to make diving easier for everyone and, perhaps more importantly for most divers, has made diving more accessible to those who are less fit and or not strongm swimmers to begin with. On the other hand, there are those who would argue that increased accessibility to persons who are not strong swimmers and very comnfortable in then water has not been a good thing.

 

[Web Monkey]

The tanks were also smaller, giving a smaller buoyancy change.

A couple of original old-timers I've talked to said they would go pickup a rock if they started getting too light at the end of the dive.

Terry

I just finished (re)watching the bulk of the first Sea Hunt season and I have a gear question.

Without a BC, how did Mike (and his fellow "skindivers") weight himself? It appears that he was positively buoyant at the surface and had to "fight" his way under. Would he go significantly negatively buoyant at depth?

In other words, anyone know how the "oldtimers" handled buoyancy and trim?

Thanks.

 

[oly5050user]

Used to wear amount of weight dependant on planned depth.If shallow more weight,if deep less weigh(allows for suit compression)...Idea was to wear enough lead so that you would be close to neutral at intended depth.You would have to do a head first surface dive to powerkick a few feet till compression of suit kicked in.

 

[fisheater]

Thanks everyone!

These replies have been very informative and enlightening. (And no one demanded that anyone else use a BP/W!)

 

[BSea]

A couple of original old-timers I've talked to said they would go pickup a rock if they started getting too light at the end of the dive.

Terry

I guess that makes me an oldtimer at 52.

But as most have pointed out, weighting is no different today than it was back then, it was just more important back then. My "Back Then" involved sitting on the couch & watching Sea Hunt on TV. I used scuba gear for the 1st time in 74, and finally was certified in 77. At 1st we used vest that were inflated orally (or in an emergency with a CO2), and I think I bought my 1st true BC in 79 (still with a CO2 for emergencies). I only made my 1st true vintage dive a little over 2 years ago. And I found out then just how important proper weighting is. And I learned about rocks.

 

[Greg Barlow]

The majority of my vintage dives are made without ever adding air to the BCD. I wear a Bare 5mm jumpsuit, a Voit Snug-Pak, steel 72, and 8 pounds on a weight belt. When diving with a full tank and at depths around 40-55', I need to use deeper inhalations to counteract the suit compression and weight of gas.

After many dives using such a configuration, it becomes second nature to make the small buoyancy changes with lung volume.

When I began diving, horsecollar BCDs were the norm. Even then, we understood that they were more for surface use than minor buoyancy changes.

Greg Barlow

 

[Luis H]

The responses you got about diving with no BC are excellent, so on a related subject about BC…

There was a time when BC's were starting to show up and they were considered only suitable for advanced divers. The danger of an uncontrolled assent due to the increased in buoyancy of the expanding gas in a flotation device was considered too high of a risk for the inexperience diver. I clearly remember the debates.

The early horse collars for a long time were not suitable as buoyancy compensators. They didn’t have proper venting provisions. They were only intended for surface flotation. Many looked similar to today’s snorkeling vests.

A few years after the horse collar had evolved to include the 1 inch hose for easy venting and an over pressure relieve valve, then the inflator was added. The inclusion of an effective quick release for the inflator LP hose was considered imperative for two reasons: 1) to ditch the tank and keep the horse collar in an emergency and 2) to disconnect the hose in case of a malfunctioning inflator.


Around 1971 or 1972 I bought a Fenzy horse collar. It had its own air bottle (no CO2 cartridge) it was considered the top emergency flotation device…”The divers Parachute”. At first it was not intended as a BC and diving in the Caribbean at the time I never thought about using as a BC. Notice left avatar picture with my Fenzy in the early 70’s.