Why a butt plate?

[Colliam7]

I'm pondering making a SM rig out of my Transpac, and was wondering about the reason for the butt plate. I usually sling a pony, and clipping it to my chest D ring and waist D ring keeps it in a position much like side side mounted tanks.

While it may seem like the attachment of a slung pony is 'much like' side mounted tanks, pony bottles attached with stage rigging can definitely 'dangle' quite a bit below the plane of the diver's body. Diving a sidemount configuration does two things: 1) the bungee pulls the neck of the tank in close to the body, 2) while clipping to a butt plate brings the bottom of the tank in close to the body.

Does the butt plate just pull the tank a little tighter to your body or what?

Yes, even after you bring the tank neck in close to your body with the bungee, the bottom can still dangle / protrude. (OK, if you are simply diving an open water sidemount configuration - not moving around in close / tight spaces, that may not be a big issue, although you are not particularly streamlined.) Clipping the bottom point of attachment of the tank to a buttplate adds the second element of 'snugness'.

with the 80's they have to get moved forward to the hip d-rings when they start getting floaty

While a number of people do this, it is not necessary if the tanks are properly weighted / configured.

Adding weight to AL80s makes it so this isn't an issue.

Very good point. More than a few divers using a sidemount configuration with a TransPac/Nomad - even in a wetsuit - may require some added weight with two AL80s. One approach is to shift some of that weight from the waist to the bottoms of the tanks. I prefer to use cambands (instead of stage rigging) on the bottom of the tanks, and I slide Halcyon (or XS Scuba) weight pockets onto the cam bands, and position some weight in the pockets (usually 2-3 pounds in each).

 

[Dive-aholic]

Butt Plates, especially the longer slides, cause pendulum swiing with tanks - recommend using d-rings, and when confident, switch to low profile d-rings. Good Luck!, cheers, Martin.

Interesting. I have hundreds of dives in sidemount with the longer slides, and have hours upon hours of video of dozens of other sidemount divers with the longer slides and have never seen swinging tanks. If the tanks are swinging it's probably something to do with the swimming technique, not the gear.

 

[scubadude105]

Yes absolutely - trained / experienced divers, with correct config, and movement / propulsion techniques - well used butt plates are great, any length. I concure. I was just reading between the lines for a new convert posting. For an average diver so-so rec/tec previously only using a front sling probably without modifying placements and simply suddenly "going" to SM with or without buttplates may be a little tricky without some assistance from an instructor, experienced buddy colleague, mentor etc. Tank movement (whatever the reason) is certainly a risk at first and may be a tad discouraging. (Trial and error - we have all been there, and I am still!). The suggestion regarding the D-rings was merely a gentle hint for a one-step-at-a-time approach. Getting the SM config down-pat, and progressing to a butt plate (maybe with the smaller side slides as in the above posted pic - very nice) would be a suggestion for an easy sequential step-wise approach. Apologies my previous entry was too cryptic Thanks, Martin.

 

[Dive-aholic]

I disagree. If you want to dive sidemount, go for it. Progressing through it in baby steps using gear you won't eventually be using makes no sense. Get the right gear and get in the water with it. A sidemount instructor or mentor is great to have around to help, but if you don't have either available to you, then just practice keeping in mind that it can take several dozen dives to get things tweaked right.

 

[scubadude105]

SM is quite addictive, and I agree thst the majority of divers who are sincere really do want to get into it and go for it. Some newbie open water / AOW students and other open ocean do want to try it, but yes the context in this forum is different, and attitude and motivation are more mature and advanced in general. Cheers to that. Just a FYI to the original post, getting back to the transpac use - when modifiying for SM, in addition to the butt plate, not sure if you have a standard pull dump-valve on your wing back of your left shoulder, eg recwing, (?unsure what type you are using), but might want to consider a plain angle coupling without the dump - lower profile for SM. Remember, you won't have the BM protection, and watch your head too. Regards, Martin.

 

[Dive-aholic]

- when modifiying for SM, in addition to the butt plate, not sure if you have a standard pull dump-valve on your wing back of your left shoulder, eg recwing, (?unsure what type you are using), but might want to consider a plain angle coupling without the dump - lower profile for SM. Remember, you won't have the BM protection, and watch your head too. Regards, Martin.

Or you can just exchange the inflator hose and dump valve so the inflator runs off the bottom of the wing and the dump is on the shoulder. That also makes dumping air from the wing effortless from a horizontal position.