Proper trim with double tanks

[WKenny]

I just started diving with double steel 85 cubic foot steel tanks and I am having a problem with trim in that I constantly feel like I am about to tip forward. I have about 100 dives with a single tank and I have my buoyancy & trim worked out nicely with the single tank, but it's like starting again from scratch with the double tanks. I have a DUI 350 TSL dry suit, BP/wing, and Turtle fins.

I keep the air in the dry suit to a minimum to allieviate suit squeeze, and control buoyancy with the wing. I have a good arch in my back and relatively heavy Turtle fins. I also have the tank in the lowest fitting position on the back plate. I hate to rely on ankle weights but I'll be trying them on the next dive. Does anyone have any advice how I can avoid tipping forward and get better trim with the double tanks? Thank you

 

[carrielsal]

Take a look at this thread. This was discussed extensively, http://www.scubaboard.com/forums/basic-scuba-discussions/335325-getting-trim.html.

 

[elan]

I just started diving with double steel 85 cubic foot steel tanks and I am having a problem with trim in that I constantly feel like I am about to tip forward. I have about 100 dives with a single tank and I have my buoyancy & trim worked out nicely with the single tank, but it's like starting again from scratch with the double tanks. I have a DUI 350 TSL dry suit, BP/wing, and Turtle fins.

I keep the air in the dry suit to a minimum to allieviate suit squeeze, and control buoyancy with the wing. I have a good arch in my back and relatively heavy Turtle fins. I also have the tank in the lowest fitting position on the back plate. I hate to rely on ankle weights but I'll be trying them on the next dive. Does anyone have any advice how I can avoid tipping forward and get better trim with the double tanks? Thank you

If those tanks are Faber LP85s they are head heavy. 2 of my friends and my wife have them and all those tanks have 8-10 lb tail weights attached to them. Otherwise they are impossible to trim out. You just need to balance the tanks. Also keep in mind that double tanks have more weight on the head. Make few weights with bolt snaps and try to attach them to your but d-ring and see which combination gives you proper trim.

 

[Diver0001]

I keep the air in the dry suit to a minimum to allieviate suit squeeze, and control buoyancy with the wing. I have a good arch in my back and relatively heavy Turtle fins. I also have the tank in the lowest fitting position on the back plate. I hate to rely on ankle weights but I'll be trying them on the next dive. Does anyone have any advice how I can avoid tipping forward and get better trim with the double tanks? Thank you

It sounds like you're doing the right things, Kenny. Maybe what you need is a trim weight attached to the bottom of the tanks.

The easiest way to do that is to thread a 1 or max 2kg weight onto the cam band of a BCD and then attach it to the tanks near the bottom. Rotate it so the lead block is right between the tanks on the top and not underneath.

That will probably get you in trim nicely without using ankle weights. After that take it off every now an then so you can see if you still need it.

R..

 

[Trace Malinowski]

Also, some divers wear their tanks too high out of worry they won't be able to reach the valves even if they adjust the bands properly. Double check the position of the tank valves in relationship to your shoulders. They should be sitting at or below the shoulder line. If the valves are above your shoulders loosen the harness to drop the backplate and tanks farther down your back. You should be able to move your head all the way back through its full range of natural motion without being impeded by the stages, isolator knob, or manifold.

 

[TMet]

I use a tail weight with my 104s. I took a crown royal bag and put holes through the top and put soft weight in it. Put the bottom bolt through the holes so it gets sandwiched between the plate and the tanks. Works well for me and its cheap. To find out the weight I needed on the tail I had a friend put weights on the bottom of the tanks while I tried to maintain trim in a pool with my hands and feet crossed. Originally I needed 6lbs but it has gone down to 2lbs over time. I'm guessing a lot of it just has to do with experience. I'm still relatively new with them but I'm finding my groove and loving them more and more.

 

[kanonfodr]

Since you are using a drysuit, you can put some air in your arms and extend them forward like you are Superman. It feels super wierd at first, but does help alleviate the feeling of "Oh my gosh I'm about to tip onto my face!!"

Also, have your buddy take some pictures of you if possible, especially from the side profile with a level bottom for reference. You may just be feeling wierd, but spot on trim.

Peace,
Greg

 

[TSandM]

I think most of us who have moved to doubles have gone through this. You're already doing some of the right things -- moving the tanks lower (and you can probably loosen the harness a bit as well, at least I could), and using negative fins. It's also important to minimize air in your feet.

When I first started with the 72s, I couldn't trim out to save my soul. I still can't trim those tanks to suit me. But even with the 85s, I felt like I needed to move weight down. I went to an Al backplate and put even MORE weight on my belt, until I finally got close to balanced.

Today, I dive the same tanks with a 6 lb v-weight . . . Same wing, same suit, same me, different balance. I wish I could explain how I learned to balance the tanks on my back, but I know it has to do with much more strict body posture than I ever needed with a single tank rig.

 

[LiteHedded]

try loosening up the shoulder straps and tightening the crotch strap

 

[RTee]

try loosening up the shoulder straps and tightening the crotch strap

...it will make you speak funny initially but you will get use to it.

Just kidding. I went through something fairly similar when I went from single 80 AL to Faber doubles 117 HP and drysuit (Fusion). Not knowing better I removed perhaps 10 lbs from what I normally used with my 7mm and then went in (when most people tend not to use any weight in that config). Almost ended up doing a face plant in the shallow section of the local quarry. Now I dive with no weight whatsoeverand I lowered the tanks slightly on my back as per the quote and it is working well. I too make minimum use of the drysuit air intake except to remove the squeeze and rely on my wing.