THE "PERFECT ( being horizontal ) TRIM" HOAX

[Curious_George]

Some divers switch to hand propulsion when panicking or when loosing control. Some others use hand propulsion properly, for avoiding to mess up things using the fins...

As normal - another great sharing of knowledge. Thank you for your generosity. Perfect example of why your likes are so much higher than your post count. Would limiting hand movement also be appropriate as a way to help improve air usage?

thanks again.

 

[dmaziuk]

Would limiting hand movement also be appropriate as a way to help improve air usage?

When you're not Doing It Right(tm). As in if you try to use the hands for propulsion you will burn a lot of energy for very little effect.

 

[scubadada]

Hi @BLACKCRUSADER

After nearly 100 posts, I keep wondering what your main objective was in starting this thread.

Not infrequently, I dive with DIR divers off boats in SE Florida. None have ever criticized my diving, nor have I ever heard them criticizing others. A buddy pair did complement me once on my ability to smoothly hold my safety stop

 

[boulderjohn]

After nearly 100 posts, I keep wondering what your main objective was in starting this thread.

I have to say the same thing. When I found out that the original post quoted something I had written elsewhere in regard to tech diving, I assumed that was the context of the thread, and that was the context of my first response. I did not realize this was the posted in the Basic Diving forum, with many of the posts referring to basic open water diving. With that enlarged context, I would like to adjust my first post to that more general context.

In general, you dive in a way appropriate to your environment.

• In open water active swimming, as is most common in recreational diving, you want to be horizontal for greatest swimming efficiency, but there is no reason you can't adjust that to match the terrain.
• If you are diving along a silty bottom, you absolutely need to be able to maintain excellent trim and use non-silting kicks.
• In certain situations, your ability to see what you are looking at is enhanced by a less horizontal pose.
• Beginning divers will find vertical ascents and descents easier to handle than horizontal ascents and descents. (For one reason not mentioned in this thread, it is easier to clear the ears in that position.)
• During decompression stops, a slight angle to the body can help in maintaining visual contact with buddies.

My comment was simply that my earlier technical training went so overboard in emphasizing perfectly horizontal trim that I became afraid to do anything else, even when it was appropriate.

 

[Angelo Farina]

When you're not Doing It Right(tm). As in if you try to use the hands for propulsion you will burn a lot of energy for very little effect.

That is another common misconception, based on seeing untrained divers using their hands in the wrong way.
Actually hand propulsion can be VERY efficient at low speed, far more efficient than frog kicking with short, hard fins.
Hand propulsion is particularly efficient for going backwards, where reverse frog kicking is the only alternative, which is highly inefficient (compared to forward propulsion).
The efficiency of hand propulsion has two causes: because you use a much smaller mass of muscles, and because the "opposition" movement has no "negative" parts, it is an "all active" action.
Problem is that almost no one is trained nowadays to use properly the "opposition" hand movement...

<EDIT> I correct myself. While these hand propulsion movements substantially disappeared in modern training of scuba divers, they have got a lot of attention in another sport: synchronized swimming.
When done properly, the "opposition" movement is very powerful ad efficient, allowing syncro-swimmers, for example, to push their legs outside the water and keeping them in that position, which requires to exert a significant vertical thrust.
In this article here below, some scientists analysed the forces involved in this hand-propulsion action, which is improperly called "sculling" in the article. In reality, sculling is a two-phases action, where half of the movement is active (the "thrust"), and the other half is providing no thrust, you are simply recovering back to the initial position ("recovery").
Instead the hand propulsion method of which I am talking is always active, as the hands change their attack angle when moving "out" and when moving "in", resulting in a constant thrust in the positive direction.
Read the paper and evaluate yourself the results...
https://www.tandfonline.com/doi/full/10.1080/14763141.2019.1671485

 

[ginti]

Problem is that almost no one is trained nowadays to use properly the "opposition" hand movement...

This is slightly OT, but very interesting. Do you have any idea why nowadays the hand propulsion technique is not common? I can only guess...

 

[JonG1]

This is slightly OT, but very interesting. Do you have any idea why nowadays the hand propulsion technique is not common? I can only guess...

Maybe because much of the trim, neutral buoyancy, propulsion enhancements stemmed from cave diving where hands could be busy, putting in jumps, placing cookies etc. but micro adjustments to position can still be required and the fins are the best/only option .

Plus a torch is used to signal and the hand movement required could be misinterpreted.

Out of OHE tho who cares if it works.

 

[ginti]

Maybe because much of the trim, neutral buoyancy, propulsion enhancements stemmed from cave diving where hands could be busy, putting in jumps, placing cookies etc.

Plus a torch is used to signal and the hand movement required could be misinterpreted.

Out of OHE tho who cares if it works.

This is my guess too.

But it doesn't explain why these techniques disappeared from the recreational curriculum

 

[boulderjohn]

Maybe because much of the trim, neutral buoyancy, propulsion enhancements stemmed from cave diving where hands could be busy, putting in jumps, placing cookies etc.

Very early in my cave training, I was in a cavern with a lot of flow, and in trying to maneuver in that flow, I used one of my hands one time to adjust my direction. After the dive, my instructor said, "Nobody passes Basic Cave using their hands." I firmly believe that was the last time I have ever used my hands for propulsion.

 

[boulderjohn]

Years ago, I was scheduled to lead a dive trip to Belize, and one of the divers was a paraplegic. Unfortunately, he got sick and had to cancel--I was very much looking forward to seeing him dive. He used special webbed gloves, and people who had seen him dive said he as able to do amazing things with them.