Doubles trim epiphany

[stuartv]

Always fun to read your posts Stuart. My question is why are you adding so much air that your trim is being affected by the shape of the wing?

I'm adding enough air to be neutral. I was wearing my trilam drysuit with Fourth Element Arctic undergarments (shirt and leggings), and carrying a SS BP with double steel 120s and a V-weight with 4# in it. In fresh water. I don't really feel like I was carrying that much weight, considering my exposure protection. So, enough air to be neutral doesn't seem like that much, either...??

If that is freshwater, then you are gonna need a decent amount of lead on a belt for the ocean. Have you tried a rubber belt yet?

I have not. I have a weight belt I made from some leftover 2" webbing and a spare buckle. It seems to work fine. I haven't used it much, but when I have used it, I've never had any trouble with it moving around on me. Isn't a rubber weight belt really more for compensating for wetsuit compression? So, with a drysuit, it kind of wouldn't really matter?

 

[dumpsterDiver]

Well..it is beneficial in compensating for suit compression, but the elasticity allows it to ride low and still not slide or spin.

With a nylon belt you have pretty much one location that will hold the belt. Often you can improve comfort significantly by being able to move it up or down a few inches during a dive to relieve low back stress. This is obviously more significant if you are wearing more lead.

i wear a rubber weight belt - even when wearing no wesuit (or dry suit). To be honest, I don't know any scuba divers who, after using a rubber belt, go back to the old nylon ones.

 

[RainPilot]

Should be around 18 lbs or so of gas weight so if neutrally weighted he would have around 1/3 of the wing filled at the start of the dive. That should be enough to accentuate any lift-distribution issues with the wing I would imagine.

 

[Basking Ridge Diver]

Isn't a rubber weight belt really more for compensating for wetsuit compression? So, with a drysuit, it kind of wouldn't really matter?

I use a rubber belt and it helps me for a couple reasons - first I don't dive with a canister light so tucking the long hose in the rubber belt makes it easier and adds a little more friction than a nylon belt - so it does not come out without a tug.
The rubber belt when cinched really stays where I put it and although I can not confirm it it seems to help control any bubbles in the suit. Or at least that is how it feels to me - my feet rarely get floaty from the bubble.

YMMV - but I wear anywhere from 19 lbs to 25 lbs on various rigs (double vs single) and the rubber belt helps me in that regard.

 

[dumpsterDiver]

Yeah i forgot that.. when wearing a tightly sealed freedive suit with a hood, the belt helps to prevent transfer from below the belt to above.. so it keeps the piss out of your ears.. a nice little benefit.

 

[divezonescuba]

I had a real foot down trim problem with AL80 doubles. Even with neutrally buoyant UDT fins and the like, I still had an issue.

I gave up messing around with the tank band positions due to the "golden rule" of doubles. Some places just don't want you to move them. At that point, I started investigating different type of weighting systems, including the use of both solid and shot keel and tail weights.

Eventually, I came up with my own solution which had to meet the following requirements:

1. Travel friendly - cannot require the transportation of any lead at all
2. Uses common locally available weights
3. Adjustable weight positions for trim variations in different exposure suits and with other equipment.
4. Horizontal trim effective - Promotes horizontal trim, correcting foot up or down trim issues.
5. Vertical trim effective - when on the surface, promotes vertical trim without fin movement
6. Rigid, robust and reliable - weights do not move cannot be lost
7. Can be used with any set of 11 inch doubles and any wing and plate.
8. Does not interfere with the operation of the gear in any way.

I successfully used the prototype for TEC 40, 45, and 50, a number of decompression dives the deepest of which was 168 feet, and the TEC deep instructor course without incident.

 

[decompression]

Fair enough, I think youre definitely at the point where you've got a good sense of your buoyancy.

I occasionally dive a similar set up, Twin HP 120's SS plate DS with fusion thermal, but in salt water and no V weight.

I'm adding enough air to be neutral. I was wearing my trilam drysuit with Fourth Element Arctic undergarments (shirt and leggings), and carrying a SS BP with double steel 120s and a V-weight with 4# in it. In fresh water. I don't really feel like I was carrying that much weight, considering my exposure protection. So, enough air to be neutral doesn't seem like that much, either...??



I have not. I have a weight belt I made from some leftover 2" webbing and a spare buckle. It seems to work fine. I haven't used it much, but when I have used it, I've never had any trouble with it moving around on me. Isn't a rubber weight belt really more for compensating for wetsuit compression? So, with a drysuit, it kind of wouldn't really matter?

 

[kelemvor]

Your post is interesting and kind of blew my mind. Not because of your discovery regarding wing shapes, but because I also use a diverite rec exp. It was part of my first bcd. However, I distinctly remember it saying 55lb of lift, and it's a horseshoe not a donut. I went over to the diverite site, which indeed lists 45lb, but the photo they show for a rec exp is not the same as my wing. The current model has less lift, bungees, and appears to have a tube of air along the bottom. I did eventually find a british scuba store selling a rec exp that looks like mine, but lists 50lb of lift.

So.. apparently, there are multiple versions of the DiveRite Rec EXP, and unfortunately they didn't do anything to the name in order to differentiate the wings.

Now, it doesn't matter to me, I'm never planning on backmount doubles. I went sidemount when I needed doubles and am happy with that config when I want redundancy. I've hemmed and hawed about getting a smaller wing for quite some time because it's far more lift than I really need.

It does make me wonder what wing I've really got though because in 2015 I had to replace the bladder. My LDS did it, with a bladder overnighted from diverite directly. I can't tell any difference except for the lack of leaks - but then I've never come close to needing as much lift as the wing provides anyway.

 

[stuartv]

Your post is interesting and kind of blew my mind. Not because of your discovery regarding wing shapes, but because I also use a diverite rec exp. It was part of my first bcd. However, I distinctly remember it saying 55lb of lift, and it's a horseshoe not a donut.

Yep. In the past, I have searched eBay for wings and I noticed that DR used to make a wing of the same name, but totally different. Mine is a donut. Definitely strange that they did that and kept the same name.

And, just for the record, I took the bungees off mine before I ever dived with it.

It is definitely nice and compact, for a doubles wing. If I ever spot a DR Classic EXP or Classic XT (which are 60#, but otherwise, the same in appearance and design to my Rec wing) for a good price, I will probably just buy it and be done. 60# should be plenty for future cold water diving with 2 AL80s for deco cylinders (when my training advances to that point).

 

[RainPilot]

I wonder if keeping the bungee on might make a difference to the shape of the inflated wing, I suspect it would even it out a bit...