Side mounting AL80's how do you trim your tanks?

[eternaljonah]

I've been side mounting every dive except open water course's since i did my course like 5 months ago and have been moving the cam bands up and down the tank, with weight added on the tank and without, but i'm still not happy, what do you guys do when diving Al80's on side mount ?

 

[DevonDiver]

In addition to cam-band location, the bungee has to be the right length. If too loose, it'll always allow the valve to drop - creating a pivot action where the tail rises. The cam-band location should be sufficiently high on the cylinder to create some lateral tension on the tank - pulling the valve down below the armpit. At the same time, it has to be low enough on the cylinder that the bolt-snap is not equal to, or higher than, the fulcrum of the cylinder. If it is, there's no way to control tail rise. The exact location is always person-specific as it varies with torso height/body proportion.

Also look at your cam-band bolt-snaps and the length of line which attach them to the cylinder. Some companies sell huge snaps (i.e. Hollis), which may be necessary for cold-water/thick gloves, but are too long to allow realistic cylinder trimming. If used as meant, in cold water, it's not an issue - as you'd probably be in negative steel tanks. Either get smaller (medium) bolt-snaps and/or shorten the attaching line. The total length of snap and line used there represents the distance variation that your cylinder will transition through when moving from negative to positive. The longer, the more difficulty getting trim sorted. You do need a bit of length though - especially if used for overhead environments/confined areas. Big bolt-snaps are the typical obstruction - and these are often sold as default if included with rigs.

Beyond that, it's just a case of properly positioning D-rings on the harness so that you can move the bolt-snap lower to counter-act progressively positive cylinder buoyancy as the dive progresses. Low-profile (tropical) D-rings also help... as they reduce the distance the cylinder can travel away from the diver positive/negative.

Some rigs, such as the SMS50 make that very hard... because the 'rails' sit lower on the torso than the waist belt. When you move from the rails to the waist D-ring, then you're actually reducing the spacing. That screws up all your adjustment on the cam-band. Ideally, you'd have to re-position the cam-band at the same time to resolve the variance. Obviously, that's a bit impractical... You suffer for the bad design... it's a rig based upon cold-water diving factors and cylinders, but primarily used in tropical locations (buoyancy insufficient for many cold-water divers) where ali tanks are the norm. Hollis should address that failure..

 

[a878bob]

What rig do yo have? Getting the cylinders to trim out is probably the toughest part. Don't get frustrated with it. Send some pictures of your rig, it will help to get some suggestions to try out.

 

[eternaljonah]

ok guys..... as you can see on both photos the setup(cam bands) are very different, each tank has a 700gm lead on the cam bands and there is a 1.2kg lead for trim at the top of the bcd, in reality i only need a total of 2 kg lead but due to tank buoyancy i have a little to much, had 1kg on each cam band before and it was still not that great,and i was heavy.

 

[Doppler]

Jonah... I think you are going to have to get yourself those steel tanks we talked about. Unless you've changed the bungees and length of the tails on the anchor clips, I know you are pretty squared away on that score.

As you know, I am not a huge fan of moving the anchor snaps partway through the dive to compensate for the buoyancy shift in Ali tanks, but that is an option.

 

[eternaljonah]

Steve no the anchor snaps are just the same i have though recently been trying out the original hollis bungee's and i like them but they do not pull the valves up as high, so i'm still undecided on bungee. have imported some too but its a little hard and slips off the valve. i guess this is where i need to find the solution
steels, i guess it will have to be i'll let Rob know to get some

 

[victorzamora]

Well, one option is to just move the snaps forward. I don't mean mid-dive...I just mean placing a d-ring on your waist. Also, how empty were your tanks when the pictures were taken? Last question: What rig are/were you diving?

One problem that is immediately apparent is the fact that the tanks are clipped to your buttplate. That will allow them to rise MUCH higher than where they should be. In fact, it seems like your leashes are way too short to be clipping off to there anyway, even with steels (but it's hard to tell from here). To keep from having to unclip/reclip the tanks, I might recommend shortening the leashes DRASTICALLY and using small butterfly clips, then clipping those to low-pro D-rings you put on your waist (you'll probably have to clip those on before the neck clip and remove after the neck clip). Full, the tails might sag a little low. Empty, they might float a little high.....but you won't have to unclip/reclip and you will never be nearly that far out of trim.

---------- Post added September 12th, 2013 at 09:59 AM ----------

Jonah: The Old School bungees I prefer 1000x over the stock Hollis bungees. Having said that, you can shorten the Hollis bungees easily by tying knots in the bungees near the quick link. Well, anywhere works but near the edges is better and farther from your tank is better. You might also have to play with where you tie your quick links to.

 

[eternaljonah]

the rig is a SMS 50 the tanks were low 50 bar each. i have been playing alot with moving things around. i have already shortened the original bungee's by clipping the two quick links together. i am going to try and see how it feels to attach the tanks to the d rings on my waist tomorrow. the lease is almost non existent the bolt snap touches the tank. i could use smaller clips though ;-)

 

[victorzamora]

Okay, it looked like you had a couple inches of leash. On the steels I'm mostly diving and am about to buy (Worthington HP100s or LP85s), the rule of thumb is to start with a ~6" leash. If you're using the Hollis stock clips, those things are HUGE! I mean, the size is really nice...but not when it's allowing your tanks to float THAT high. I've switched to smaller butterfly snaps for all tank connections. They have their good and bad, but I like them so far.

I've got a buddy that owns a Razor for SM AL80's and he just moves the clips forwards. I'll be heading to Mexico and I'm hoping to get Jason Renoux to help me get my AL80 setup just right. I'm diving a Hollis SMS100 with Edd's mods done to it. I'm looking at making a custom harness, but I'm still struggling with exactly how to get the AL80s to behave. If I get it figured out, I'll let you know. If you figure it out, let me know!

 

[DevonDiver]

ok guys..... as you can see on both photos the setup(cam bands) are very different, each tank has a 700gm lead on the cam bands and there is a 1.2kg lead for trim at the top of the bcd, in reality i only need a total of 2 kg lead but due to tank buoyancy i have a little to much, had 1kg on each cam band before and it was still not that great,and i was heavy.

View attachment 165834View attachment 165835

Your cam-bands are WAY too low and you are still attached to your rails. You need D-Rings on the front of your hips...and your tanks should have been moved down to those attachment points long before (normally around 110-130bar).

Reference my points made earlier about the SMS50. Strange how I predicted you were diving that, based on the problems you're experiencing (they're common problems with that rig, because the SMS50 has silly rails, no waist D-Rings and comes supplied with humongous bolt-snaps).

My advice... forget the rails. Start on the rear D-Rings and add some D-Rings to the front of the waist strap. Get some medium sized bolt snaps and use just 1" of cord free to where they secure on the cam band. Cam bands should be approx two hand widths from the bottom of the cylinders.

The bungee looks ok in length... but replace it anyway... the one supplied by Hollis is abysmal and WAY too strong. Get some 6mm bungee and use that instead. It's much easier to work with.

See here, one of my students showing good trim throughout a Tec Sidemount training dive (Stealth rig):



...and here is a student in SMS50 (properly rigged/modified) with AL80s, also on a Tec Sidemount course:



No offence, but why don't you just seek some expert training and get it perfected in 2 days?