How to "trim"?

[Scoobidoo]

I have recently converted from a jacket to BP/W! And as a newbie here, can someone talk me through how to get the right "trim"? For instance, how and where to move weights around and what are the things to look for to get my trim right?

Thanks!

[in_cavediver]

Well, first, lets define trim so you know what you're looking to get to.

In trim, simply means in a neutral hover (no kicking or moving), you are very nearly horizontal and have no tendancy to roll, flip or go head down/up. IE, stable.

Now, how to achieve this. This is the good part. Some rough bit can be done via the internet but you'll have to account for the fine details yourself in the water of lots of dives. So GO diving. See, being told to go diving is good.

First, set you tank in a location on the BP that gives access to the valve and rides comfortably, then do a weight check with your exposure protection to see how much weight you need. From there, its placing weight and the tank in order to level you out.

From when I used to DM, we would put 2-3 lbs of weight on the upper tank strap for an AL 80 for just about everybody in a 7mm farmer john. (a single ankle wieght is a good altenitive for expirementation). That coupled with good tank placement did a lot. Now, different wetsuit, different needs.

[Manny-R]

what way are you in the water? like / or like \ (head down) once you find that out (have your buddy watch you) then start moving weights/ tank placement, till you get it right.

[Scoobidoo]

Hey, thanks guys! That will be a great start!!

[kobalap]

Edit: Sorry, I thought this was DIR focused forum. The content in this article assumes DIR kit but the principles apply regardless of gear.

This article was written by a former GUE instructor from Northern California. It is posted publicly in their forum (forum.5thd-x.com). The original article had images that illustrated some of the points however, those images are now broken links.


The Importance of Balance

What is it?

Balance is perhaps one of the single most important factors in our diving. From how we sink to how we hover, balance is a complex equation dealing with not only how much weight to use, but where to put it. Factor in a variety of body types, environments, and exposure protections, and you have a dizzying combination of variables that is difficult to unravel. Stack on top of that the importance of trim, awareness, and the ever changing role of an air bubble underwater, and it's not hard to understand why some people describe good balance as an art as opposed to a skill. Truth is, the secret to effortless trim is good weighting, and that's what we're here to discuss. The benefit of having good trim is not so you look pretty (although you will Smile). You'll use less gas, have less difficulty with buoyancy, and reduced impact on the environment.

In this equipment education, we'll focus on the aspect of weighting as it applies to balancing your system.

What is Static Instability?

When I first took my Advanced class, I had on a Scubapro mini-72, and 30 lbs of lead with a two-piece wetsuit. My instructor said I had no problems sinking. That's a serious understatement. I was probably 15 to 20 pounds overweighted. Needless to say that balance was not my forte.

For the average diver, who's not quite so overburdened, static instability is the instability caused by placement of equipment that is negative buoyant. 'Static" means that, as long as the equipment is held in place by a reasonable configuration (i.e. backplate and harness) it won't be changing throughout the dive, or as the diver moves (as compared to the bubble inside the drysuit.) Instability can be a lot or a little, depending on the size and placement of the equipment.

Consider which aspects of your equipment are negative. For the average DIR diver, this includes:

- backplate
- tanks
- weight belt
- canister light
- jet fins

Within the DIR system, we place these items in where they go, based on what we need them for. The tanks need to be mounted up near the head for breathing accessibility, and valve manipulation. The light needs to be mounted on the right hip to assist with capturing the long hose, as well as to be ditchable, and the fins need to go on your feet and not your hands (regardless of how much we tried to use our hands to swim Smile). In general, this configuration works well for most anyone, but problems can arise that affect our ability to maintain horizontal trim: namely, tank selection and weight placement.

Consider the diver in trim.


They are much like a see saw, with two opposing arms, and a center of gravity.


Depending on their configuration a diver in good trim (i.e. head up, back slightly arched, and knees up by flexing the glutes) has a center of gravity based on the distribution of their weighting. Not many aspects of this system are flexible. Moving the fins closer or farther away from the tanks may allow for some minor adjustment, just as moving weight closer or farther away from the center of the see saw affects the balance.


But far more influential is the placement of the largest sources of weight, the tanks and the weight belt.

Tank Selection

Tank selection is a bit of a hot button topic, as many would pronounce only one tank was worth diving for everyone. Given the variance in human body types (Delia is 5'2ish, Andrew is 6'6ish) and tank availability, I refuse to believe that only one tank is right for everyone. Things to consider when selecting a tank.

1) If you're in a wet suit, stay away from double steel tanks. Too much weight may prevent you from either a) staying at the surface, or b) returning to the surface in the event of a BC failure. Instead of getting redundant bladders, choose tanks that aren't too heavy for your exposure protection (read: Aluminum).

2) If you're tall, a short, negative steel tank (such as a E-series 80, HP80, or Scubapro mini-72) is a bad idea. The tank must be mounted so that you can get to the valve, but doing so places most of the weight far from the center of gravity. This can result in a head down posture due to the increased weight on the top-half (or "north") of your body.

This can also lead to a "wheelie" type posture.

You account for the increased weight by changing your trim to to a 45 degree angle. This effectively reduces the length of your "north" arm, allowing you to balance. Unfortunately, it does nothing for your trim, and increases risk of silt, getting your fins entangled in the line, and loss of buoyancy.

Ideally, you choose a tank with dimensions that distribute a reasonable amount of weight over a larger surface area. Normal to longer type tanks distribute weight more evenly than short, fat tanks.

For divers that don't require a lot of weight in the water, too much weight may be caught up in the tanks. This is especially true of using steel tanks in freshwater, as the increase in weight (due to the decrease in buoyancy) may lead to some drastic overweighting on the North of your body. However, the solution is to be had in weighting as well.

Weighting

Determining how much weight to carry

The first problem with weighting is that everyone is usually carrying too much. This stems from our first days in the pool in Open Water class. If we couldn't stay on our knees, or weren't very proficient at dumping gas from our wing, the first solution was to increase weight. This creates an incorrect notion that increasing the ballast increases stability, when, in fact, nothing could be farther from the truth. Increase the weight actually increases the amount of gas you need to keep neutral. The larger the size of the bubble in your BC, the larger the changes are from little lapses in buoyancy, such as a deep breath or a bit of surge.

Therefore, we need to reduce the weighting as much as possible. Unfortunately, not many divers are taught when to check the buoyancy. Often times, checks are conducted at the beginning of the dive, when, in fact, they ought to be done at the end. We are at our lightest at the end of the dive, with very little gas in our tanks, and this is where the buoyancy check ought to take place.

It's simple to do. With your buddy close at hand, at the end of your dive, drain your gas to 300 psi (20 bar) or so. Then, with reg in place, dump all the gas from your BC (and drysuit, if applicable) exhale, and don't kick. If you sink like a stone, take off some weight, give it to your buddy, and try again. If you don't sink, add some weight (small amounts, 2 lbs/1 kg or so). Get to where you sink slowly (i.e. 1-2 seconds to get fully underwater) but evenly. It's true, compression of neoprene means you'll be slightly heavy at your 10'/3m stop, but you're in the ball park. Realize that if you sink at the end of the dive with no gas in the suit, you'll have no trouble sinking at the beginning of the dive with a full tank. Also realize this assumes no kicking, no gas in the wing, and very little gas in the suit.

(Instructor note: If you think you're underweighted because you just shot to the surface, compose yourself, and if it is safe, attempt to descend by dumping everything. If you sink, it wasn't the lack of weight that shot you to the surface Smile)

Proper placement of weight

Now that we have the correct amount of weight, let's consider how to position it. Single tank divers and double tank divers have different issues going on, so we'll address each separately.

Single Tank Divers

Most single tank divers have a weight belt. Depending on their exposure protection and their tank selection, this one piece of equipment can cause the most problems in terms of balance. Requiring 20 pounds or more in one location means you'll have serious issues with balance. If you consider the see-saw example again, you'll see that having that much weight can often tip the scales to the rear.

Quote:
I can't keep my knees up


Solution: move more weight to the north.

There are several different solutions for transferring weight to the north.

1) Weighted single tank adapter. It works with almost any plate, and places an additional 6 pounds of lead over the plate to offset that weight on the belt. Works with almost any wing, although not quite as nicely with the Halcyon Pioneer.

2) Trim weight pockets. Allows you to move small pockets of weight further north by attaching them to the tank bands. Be careful, as placing too much weight up north can have the opposite affect. Also be sure to balance them left to right as well. And finally, realize that the higher you mount the weight, the more likely you are to roll. But these are great for custom tweaking of the amount of weight you'd like to shift, and also good for travel.

3) DSS Bolt-On Weight plates - made to bolt on to our Medium Deluxe Plate, these weight plates add a low-profile 8 additional pounds to the backplate.

Quote:
"My weight belt doesn't work as I don't have the LoJo booty"


1) Halcyon Active Control Ballast (ACB) either 12# or 20# 20# will help keep the weight on the harness. Keep in mind, you do have more flexibility with the belt, as you can shift it either north or south as your needs require, but having it nice and tidy on the harness is also a viable option.

Keep in mind, as you move your weight off your belt or waist, it often becomes unditchable. If you place too much weight in a non-ditchable location, you may place yourself in a dangerous scenario. An easy way to check is, at the beginning of the dive, dump all the gas from your BC and attempt to remain on the surface. If you can't, then you need to have ditchable weight. Also realize that if you are in a wetsuit, you'll experience compression, so that even if you're able to stay at the surface, the compression of the suit means you'll be even more negative at depth, thus making it even harder to get shallower.

Doubles divers

Usually, doubles divers have the opposite problem. The combination of loss of weight belt due to steel tanks and drysuits leads to them feeling as though they are going to go butt over teakettle.

Quote:
How do I alleviate that head-down feeling


1) Aluminum Backplate - Obviously, we need to reverse the solution; getting weight from the North to the South. The AL plate will take 4 pounds out of the plate, and allow you to shift it wherever you want it to go.

2) Different tanks - while not the most popular, certainly tank selection can change the weighting scheme. Instead of 104's or 130's, consider 80's or 100's. Also consider AL80's. While not the most efficient in terms of weighting, they dramatically reduce the amount of weight on the North of the diver, and require additional weight to keep the diver neutral with empty tanks. While I hate carrying additional lead, if you can't keep your head up, balance is everything, and like a scooter, it's easier to trim something that is positive than negative.

3) V-weight modification - the standard v-weight is designed to lay between the bolts on a set of doubles. But if you cut one in half, you can create a 4-6 pound weight for just the bottom of the doubles. The soft lead is easily cut by a hacksaw.

Quote:
How do I ditch the weight belt?


As a doubles diver, you have a couple of options

1) V-weight - 8#and 11# - a low cost solution that allows you to stick a good chunk of weight between your doubles.

2) DSS Bolt-On Weight plates - as with the single tank divers, doubles divers can also take advantage of these plates to remove weight. The lower profile will also reduce roll tendencies.

[Manny-R]

holly geez.. that is long!!

[kobalap]

Originally Posted by Manny-R

holly geez.. that is long!!

Yeah, it's pretty comprehensive. But personally, I think the information is extremely valuable.

[Manny-R]

Originally Posted by kobalap

Yeah, it's pretty comprehensive. But personally, I think the information is extremely valuable.

i just read it and have to agree, it is pretty comprehensive. did some of it get cut off? can i have a link to where you got this please.?

[CompuDude]

I think that's an uncredited copy/paste from GUE's website.

[kobalap]

Originally Posted by CompuDude

I think that's an uncredited copy/paste from GUE's website.

I tried to give credit. See below.

Originally Posted by kobalap

This article was written by a former GUE instructor from Northern California. It is posted publicly in their forum (forum.5thd-x.com). The original article had images that illustrated some of the points however, those images are now broken links.

The entire post is available under:
http://forum.5thd-x.com/viewtopic.php?t=978

I am making a couple of assumptions though. I am assuming that since this material is publicly available anyway, the original author is okay with the content being reused for as long as there is no "profit" involved. I am also assuming that this type of a post is not a violation of TOS.