Now what? (BP/W)

[Dryglove]

Thats odd. I have used a fredt heavy plate with double 72's and PST E7 100 doubles with no problem and had room for for one of his v-weights to go between the bands and backplate spine.I used highland bands so maybe that made a difference.

However, if you want to use the plate for doubles, rethink the Fredt. My cavern instructor & I set his doubles against my plate, & the tanks did not contact the outer edges of the plate, rather, the bands on the doubles contacted the U-bend of the plate. This might cause you problems with the doubles having unwanted movement. As soon as I can get around another set of doubles with my plate, I am going to get some pictures to send to Fredt, as he has requested.

 

[cool_hardware52]

I own a Fredt plate with an OxyCheq 45 wing. While I have a Koplin STA that has slots for the tank bands in the STA itself, I just checked to see it the slots in the plate & the wing line up. Yes, they do.

However, if you want to use the plate for doubles, rethink the Fredt. My cavern instructor & I set his doubles against my plate, & the tanks did not contact the outer edges of the plate, rather, the bands on the doubles contacted the U-bend of the plate. This might cause you problems with the doubles having unwanted movement. As soon as I can get around another set of doubles with my plate, I am going to get some pictures to send to Fredt, as he has requested.

This post is not intended to be pro or con any particular approach, just information.

Some believe that it is imperative that the center channel of a BP actually contact the tank bands so that the bolts won't have any unsupported lenght that might cause them to bend. Plates with a very deep channel and a "Steep" bend between the two halves can result in exactly the situation described above, i.e. the tanks themselves do not contact the plate. This places the tanks farther away from the diver, (valves anybody?) may allow the tanks to rock, and does not trap the wing between the tanks and the plate.

Given the possible combinations of tanks / manifolds / bands, the maximum depth of the center channel before it bottoms out on the tank bands can be difficult to determine.

With a shallower center channel and flatter bend in the plate the tanks are sure to contact the plate, trapping the wing at these points of contact. While true that there will be some "unsupported" lenght of bolt between the bands and the plate, the bolts are loaded primarily in tension, i.e. they are mostly pulling the plate onto the tanks. The friction between the tanks and the wing and the plate is what holds them in place.
This approach places the tanks as close to the diver as possible.
The possible downside is tank bolts that are too short to reach a shallow channel / flatter bend plate.

Either approach can work, but it does point out the merit of making sure, far enough in advance that a particular set of banded doubles will work with a particular BP&W.


Regards,


Tobin George

 

[scubafool]

lal, I think I will contact my instructor to find out exactly what he had as his tanks/bands, but I think the tanks were steel 85's. The reason we tried this experiment was because he had a student the week before with a Fredt plate & doubles who had a problem with the tanks rocking.

Tobin, I am not 100% certain, but I think I recall that the bands contacted the corners of the channel, & not the flat end of the channel.

 

[cool_hardware52]

lal, I think I will contact my instructor to find out exactly what he had as his tanks/bands, but I think the tanks were steel 85's. The reason we tried this experiment was because he had a student the week before with a Fredt plate & doubles who had a problem with the tanks rocking.

Tobin, I am not 100% certain, but I think I recall that the bands contacted the corners of the channel, & not the flat end of the channel.

Dear ScubaFool,

What you describe is amoung the possibilities with deep channel plates, i.e. an interference between the "corner" of the channel and the curved part of the band. Even if the "front to back" measurement across the flats of the tank bands was a constant (and it is not) the distance between the tanks are not. Some set ups have barely enough clearance for the bolts ~.375" or less and some almost allow you to stick your arm between the tanks. This is a function of the manifold and tank diameter.

Wide spaced tanks obviously will interfer less with deep channel plates. Smaller diameter tanks are often wider spaced as the center to center distance is set by the manifold.

I've also seen cases where deep channel plates bottom out on the tank bands directly ( the flat part of the channel hits the flat part of the bands ) and the rocking was caused by the wing grommets. The wing grommets are often not nice and flat like a washer, but kinda round. They act like pivot points.

Shallow channel plates do not suffer this problem, but shallow channel plates may require slight bolt lenght adjustment.


Regards,


Tobin