It took me a while to discover this; as you say it's counterintuitive. It's because in backmount for a given set up your centre of gravity is fixed but your 'centre of buoyancy' is not. If you are head heavy, cofg too high up the body, you become stable when your cofb is also high, which means the air in wing is also concentrated high. If you move the cylinders lower, or move weight lower, the air in your wing also has to be kept lower, more in the centre of the bladder, which means you have to tilt forward. For my Apeks 40 the cofb can actually move a foot and a half depending on angle in the water. I've found it much easier in sidemount since my XDeep wing keeps the air more or less in the same place in the small of your back over large trim angles and achieving correct trim is then the intuitive way of moving weight from the low end toward the high end.
You've described perfectly my tendency to trim out slightly head up because I'm afraid of going ass over teakettle if I try to get perfectly horizontal, and yes, I've been told I'm head-heavy. What complicates this is that I'm wearing Jet Fins that weigh about 16 tonnes each -- and when I try to trim out and remain stationary for drills, my feet tend to sink, so I'm kicking constantly to stay in trim. Putting a little gas in the feet of my drysuit tips the balance back the other way, so I've tried putting weights in my thigh pockets ... I tried going from a steel backplate to aluminum, but then I ended up adding more weight below the bottom bolt. What's continuing to elude me is maintaining that stable platform where I'm horizontal from shoulders to knees, while my knees are bent at a 90 to 120 degree angle and my feet are floating effortlessly with my fins horizontal. It seems like no matter what I do, I'm still having to kick up to keep my feet above my centreline. I've tried lighter fins, but I don't think they're going to be the magic bullet either.
I moved my weights down on my wing to correct my overall trim, then fine-tuned my heavy feet by getting lighter jetfins. OMS Slipstreams work great for me.
My instructor! I struggled a lot with trim when first learning, and eventually it got comfortable, but it's something I'm going to try and pay attention to and get better at. One good tip for reaching your valve on a single tank is to make sure your elbow is pointed forward and not flared out when reaching back. I struggled a ton with this, and it's still not easy for me to do, but I can reach it. I also stretched my tricep muscle quite a bit. You can place your elbow on a wall and press forward, or do a towel stretch behind your back.
Good stuff, moved to tec recently and am still slightly head up but have my tanks on the highest setting on my backplate. Will move them down this weekend, hopefully will still be able to do s drills in my dry suit when down a notch.
During a pool session trying to find my trim, I strapped the weightbelt to the tank (not a good idea in OW). By moving the center of mass upwards, this "problem" became even more apparent. As soon as I leaned too much forward or backward I would start pitch without control. Most PADI trim theory doesn't seem to mention the importance of a centered or low center of mass.
I did my first dive with twin steel 100s this weekend getting ready for fundamentals course and exactly what was happening to me, I was so head heavy I could not get trim or relax was brutal. Also my crotch strap was to loose as well. Willl try this on the weekend on next dive. Or should I use twin 80 aluminum first and get use to doubles first ?
See if you can move your tanks down a bit. The type of tank shouldn't make a difference if they're above your center of gravity. Only if they're off-center will they make you pitch to head or feet.
@@Yggdrasil42 Actually moving to lighter tanks will allow you to put more weight where needed in terms of trim. For example I switched to aluminum tanks and put more weight on a tail pouch as I tend to be head heavy. Also, 1lb weights in the thigh pockets works better than one would think due to the long arm from your CG... Once you get to that sweet spot that Francesco describes the feeling is awesome - no more fighting!
As per the video, if you tend to pitch forward, head down, your cofg is likely too low and you should try moving tanks or weight up your body. As he says, it's counterintuitive but it works.
@@timgosling6189 Hey Tim, thanks for the note. However my understanding of what Francesco is suggesting is if you feel head heavy (and therefore compensate by swimming in a slightly head up position to get your CB up in your shoulders) to move your tanks aft, i.e. towards your feet, to get your CG towards your feet and being able to relax in that position. Note this presumes using negatively buoyant tanks, hence my note re: AL tanks (which are buoyant at the end of the dive) and moving the weight that counters this towards your feet instead...
Just did my padi aow. I must be very leg heavy as I was having a fucking nightmare staying horizontal. After the weight belt drills I ditched it and put 4 kilos at the top of my tank. Seemed to fix most of my issues.
If you are leg-heavy, it doesn't make sense to bring down the tanks. If center of buoyancy higher than the center of gravity, you get more torque in the wrong direction. Let's take the two major components: - tanks have just about the same position for center of gravity and center of buoyancy. - the divers body usually has a discrepancy between center of gravity and center of buoyancy. Gravity center more towards the legs and buoyancy center high to the torso. Now combine both... the tank should be positioned to counter the torque of body gravity-buoyancy torque somehow.
Great thought. I’ve been diving like a seahorse for a while battling my trim. Trying different things to remedy but nothing seems to fix it. Definitely going to try dropping my 71 doubles to the second grommet on my bladder. Thank You 🙏🏽💯🤿🏴☠️
S o glad you raised this point, there's a fantastic series on GUEtv rthat should help with this gue.tv/programs/better-diving-through-fitness-precision
