Comments on: Horizontal Trim 101 – Uses

By: SeaJay Bayne

SeaJay Bayne — Thu, 04 Mar 2010 13:32:37 +0000

Nicely done! A great explanation – with excellent illustrations – about the basics of trim, and the only place I’ve seen an accurate explanation of the control of “angle of attack” using the “bent knees” method.

By: Don

Don — Mon, 19 Oct 2009 22:20:14 +0000

Jude,

Thank you for reading the post.

Adding equipment can absolutely affect yaw control. This is additional weight pressing down on one side of the body.

Most people will naturally compensate for 1# of difference by body position alone. >2# requires either adjustment of weight or use of the BC.

The best example of this is diving a stage. With a Wing style BC, the weight of the stage can be compensated placement of air (buoyancy). More gas is put into the side of the wing that the stage is on. As the stage gets lighter from use (gas is consumed), then less air is needed in the BC to compensate.

My recommendation is get familiar with using air side to side to compensate, especially for stages which change weight during the dive. For fixed items, shifting weight around the weight belt is fine.

Best of luck.

-Don

By: Jude

Jude — Mon, 19 Oct 2009 14:23:20 +0000

Don,

Thanks for this post. I agree that the fulcrum explanation makes the concepts accessible. What I am finding, now that I’ve added a primary light to my single-tank kit (wetsuit) is that my issue is now yaw control rather than pitch. Having removed the 6-lb tank adapter weight upon adding the light to avoid being overweighted, I found my first dive required a lot of work to maintain trim without rolling to the right. I am going to try adding 2 lbs to the left side of my top cam band and will let you know how it goes. But, I guess my point is, adding equipment can have an effect on the yaw plane as well as the pitch plane. If I were diving a stage, the light might be balanced by the stage. But, for now, I don’t see another option other than a cam weight. Have you experienced the same issue?

By: harold

harold — Sat, 10 Oct 2009 11:21:03 +0000

The best informations i ever found about TRIM, and i searched a lot, are here.

By: Don

Don — Mon, 05 Oct 2009 02:25:43 +0000

Thank you for feedback. The purpose of the post is for practical application and focus is explicitly on the pitch plane.

As such we can discuss this in terms of fulcrum and levers around this fixed point.

However, if you have a suggestion for making this concept easier to understand and implement, please let me know.

By: Gabrielle K.G.D.

Gabrielle K.G.D. — Sun, 04 Oct 2009 18:18:44 +0000

From a standpoint of physics, this is a horrible analogy. The condition you describe, balancing the positive forces of buoyancy with the negative forces of weight, are more akin to a beam load. With the shifting of weight, volume and centers of gravity you describe, as well as the corresponding moments and moduli, more accurate descriptives, as well as mathematical proofing, can be provided. Your theory that the body rests on a fulcrum, while floating in the water and constantly changing weight distribution, is completely inaccurate. Unlike a body in the water, subject to the changes in forces brought on by buoyancy and pressure, a fulcurm would be a fixed, unmoving, unreactive point. While your theory may seem reasonable while trying to teach a layman, it is not what is actually happening in practice.