Question Trim position in a BPW?

[jellycatsdad]

The only reason you would possible need a wing with more lift is if you decided to attach a load of non ditchable weight to your rig and/or if you went to a 6 lb steel plate and a bigger steel tank.
If your weighting is dialed in now then your OVERALL weighting isn’t going to change.You’ll just be taking some off the belt and adding it back onto your rig higher up where you need it to trim out.

Yea, I think the most I’ll tank wise are my current LP95s or HP100s. HP100s felt better. But, it will be nice having to take off at least 4-8lbs of lead off my weight belt.

 

[Still Kicking]

Ok, so next dive what I’ll do is get my tank higher - but not so high that I bang my head against the valve/first stage. And I’ll give the 4lbs of weight on the valve a try.

Eventually, I’ll buy another BPW, this time something with a steel plate and 35-40lb wing to deal with future drysuit diving. I can swap out the plate for steel if I wanted to as well.

Another observation I made - in the pool wearing just a dive skin or baggies and using an Al80, I needed 5lbs of lead in a cam band pocket. With the LP95, I needed 4lbs.

Four pounds is a lot to add to the valve but see how it goes. Small changes in weight distribution can have a big impact and the end goal is to find a balance. But you will see the difference immediately and adjust accordingly.

I tend not to put weight on cams, especially if you already have extra weight up high (horizontally speaking) on the tank valve. Weight above your horizontal midline can have a tendancy to roll you.

I like to have most of my weight low horizontally to increase stability (most weight at or below midline to offset buoyancy above the midline). Think of an airship (but not the Hindenberg Lol).

But it never hurts to experiment with weights in different places and see what happens. You'll get the picture right away.

 

[lowwall]

Get a pair of the small trim pockets that hold up to 5 pound hard weights and put them on your upper cam band right next to the plate. You can now easily experiment with up to 10 pounds of weights up high.

You can do the same with the lower band as well if you further experiment with your trim or get more weight off your belt. For example, if you put a 2 pounder in each of 4 pockets, you are basically mimicking the effects of a heavy steel backplate.

I use these (on my waist belt, that's enough for me with a steel plate in warm water), they are secure and inexpensive: https://www.scuba.com/p-xsstwbk/xs-scuba-single-weight-pocket-black

 

[rongoodman]

Seahorse trim can be caused by being leg heavy, but it can also be a defensive measure when you're are head heavy. The only way to be sure is to put yourself horizontal, stop kicking/skulling/moving, and see which way you rotate. A buddy's guidance is helpful to tell you if you are actually horizontal.

This is often a problem when people move to doubles and need to compensate for the extra weight up high. That short steel LP 95 with all the trim weight might be doing something similar. I've only used them once, on a trip to the Red Sea, and I don't remember them affecting my trim, but that was with a steel BP and no extra trim weights.

 

[happy-diver]

Okay let's say I'm a 6'4 dude wearing a Farmer John and jacket 5mm wetsuit so that's 10mm
covering my torso, wearing a jacket bcd, steel 120, plastic fins, and a 14kg - 30lb weight belt

There I go diving do do do da da da swim swim swim horizontal here and horizontal there
no matter if I'm in one metre of water, I'm off the bottom horizontal, or three metres there
I am horizontal, same in ten metres and the reason I'm giving shallow examples is because
it all requires a bit more control at shallow depths, and even at 50metres I'm horizontal if I
want to be horizontal, so what happens when I stop swimming, do I stay in horizontal trim

Yeah I remain horizontal, but only until I decide to release the torsional rigidity, or tension
in my body, with which I control my diving then with all that weight belt I'm going vertical


Trim must start from a stable platform, not a pound here or there, it's not the gear it's you

If you dive like a sack of lemons hanging from a hook well that's how you will forever look

 

[MB NZ]

That's the thing, you can compensate for gear which isn't well balanced (in the trim sense) with posture, but that requires extra energy and thought. I'm too lazy for that!

 

[inquis]

Another observation I made - in the pool wearing just a dive skin or baggies and using an Al80, I needed 5lbs of lead in a cam band pocket. With the LP95, I needed 4lbs.

There is something wrong with these measurements. If only the tank is different, there should be about 4.5 lb difference in lead between these cases. Could be different amounts of gas in the tank, incomplete venting of the wing, trapped air in the suit, or different amount of air in lungs. ETA: I'm assuming Faber LP95 and Luxfer AL80.

This can be easily verified with a luggage scale and weigh them in the pool. Air weighs 0.08 lbs per cuft, if you need to compensate for differing amounts of air in the tank.

 

[inquis]

For consistency and ease of measurement, I like to find the amount of lead needed to be neutral at the end of a normal exhale. This is easy to hit repeatedly, unlike the vague "lungs half full" or similar guidance. For the actual lead needed, just increase that amount by the weight of the gas less 1 lb. (If you have to breath that last lb of air in an emergency, you can remain neutral with a slightly larger exhale.)

To convert psi of air to lbs of lead to find that adjustment, divide the pressure by 379 (LP95) or 512 (AL80). For instance, if you are neutral with an AL80 with 2000 psi, the increase would be 2000/512 - 1 ~= 3 lb to add to whatever lead that made you neutral. This way, there is no need to drain the tank down to reserve pressure.

 

[Still Kicking]

For consistency and ease of measurement, I like to find the amount of lead needed to be neutral at the end of a normal exhale. This is easy to hit repeatedly, unlike the vague "lungs half full" or similar guidance. For the actual lead needed, just increase that amount by the weight of the gas less 1 lb. (If you have to breath that last lb of air in an emergency, you can remain neutral with a slightly larger exhale.)

To convert psi of air to lbs of lead to find that adjustment, divide the pressure by 379 (LP95) or 512 (AL80). For instance, if you are neutral with an AL80 with 2000 psi, the increase would be 2000/512 - 1 ~= 3 lb to add to whatever lead that made you neutral. This way, there is no need to drain the tank down to reserve pressure.

Or you can do a weight check with a full tank at the beginning of a dive; get your weighting so you're neutral at the surface, add 5lbs and you'll be in the ball park.

 

[inquis]

Or you can do a weight check with a full tank at the beginning of a dive; get your weighting so you're neutral at the surface, add 5lbs and you'll be in the ball park.

Yep, though neutral *at end of normal exhale* is kind of important. Otherwise you're compensating for the gas weight twice.