Spg, AI, both

[Jersey1971]

He dives sidemount, so this may be why he's insisting on 2 separate transmitters. He also had trouble remembering the correct hose routing for doubles, which cast some doubt on how familiar he is with the setup. And tried to disassemble second stage from hose by cranking on the parts of the connection that are fused together. I don't want to derail this thread any further, so I'll start a second one to sanity check my setup. I think I might do AN/DP elsewhere....

 

[BlueTrin]

Had a discussion with my instructor wether AI alone is safe enough or not I believe they are enough in them self he believes you have to have a spg and a transmitter. Got my curious what a peoples preference and why

In the past some AI transmitters were unreliable. Anyway diving with one does not compromise safety since you will abort the dive if it fails, like a SPG.

At the risk of derailing the thread, how many use 2 transmitters while diving doubles with a manifold?

Never met someone doing this, but then I don’t go around inspecting absolutely everyone’s kit on a charter …

 

[Belzelbub]

It's silly to use both and defies logic. Some divers love to clip every piece of equipment they own on to themselves. Even instructors.

Next time ask him why he recommends both.

Yep. Agreed.

For the most part, transmitters are quite reliable these days. Early ones, not so much. Those early ones may have tarnished the reputation of transmitters in some peoples minds. I never use them, and have been quite happy with the performance of my PPS transmitters.

OP,
I expect the answer will be in case the transmitter fails. Then ask about what to do if an SPG fails. Does the instructor recommend people carrying two SPGs? With single tank/1st stage recreational diving I've never seen, or even heard of, a diver using two SPGs. Transmitters and SPGs can both fail. The failure mode for a transmitter is preferable to me as there is no mistake. I've seen an SPG fail underwater, and it failed by just sticking at a pressure. That could get missed. There is no mistaking a No COMMs message on your computer.

A lot, however, will depend on your typical diving. I dive primarily off of my own boat, so don't generally need to keep a schedule. I bring a spare SPG (or 3) in my SAD kit. So aborting a dive, swapping to an SPG is not that big of a deal, and I could probably get it done before my computer timed out for a continued dive. If diving with charters, they have a schedule, so doing a swap mid dive likely won't happen.

 

[Altamira]

As a rec only diver, who mostly dives from a scheduled dive boat, I appreciate redundancy. The decision as to what to carry is as simple as this:
If I have only one AI (hosed or transmitter) and no SPG, if the AI fails, I have to abort the dive.
If I have only one SPG and no AI, I have to abort the dive if the SPG fails.
If I have both an AI and a SPG, and one fails, I can complete the dive, as well as the one following.

However, I don't think less of other divers that make a different equipment decision. "Silly" is not a term I would apply to any diver's decision as to whether to have a backup source of knowing remaining air quantity.

 

[Brett Hatch]

I dive with both, but I'm not particularly religious about it. Used to dive with just the SPG, and added the transmitter when I purchased an AI computer three years ago. I might remove the brass SPG some day, or might not.

I have heard a lot of reasons for removing the SPG: higher failure rate, higher complexity, increased drag, and so on... I don't find any of them to be very compelling. The main reasons I haven't removed the SPG yet are, it's nice to check once in awhile and see the same number in two places, it keeps my left hand in the habit of manipulating the SPG bolt snap, and it allows a buddy to read the SPG without needing to ask. Those reasons aren't all that compelling either, so maybe the real reason my SPG is still on there is laziness

 

[JohnN]

+1 for lazy

 

[CuzzA]

As a rec only diver, who mostly dives from a scheduled dive boat, I appreciate redundancy. The decision as to what to carry is as simple as this:
If I have only one AI (hosed or transmitter) and no SPG, if the AI fails, I have to abort the dive.
If I have only one SPG and no AI, I have to abort the dive if the SPG fails.
If I have both an AI and a SPG, and one fails, I can complete the dive, as well as the one following.

However, I don't think less of other divers that make a different equipment decision. "Silly" is not a term I would apply to any diver's decision as to whether to have a backup source of knowing remaining air quantity.

Before AI did you dive with 2 SPGs?

 

[Pressurehead]

Both.
Let us flog this horse again.

Sorry, had to be done.

 

[scubadada]

I dive both. I have never missed part of a dive or a series of dives. Over the years I have had a number of failures requiring backup. How hard is it to have an SPG attached to you left chest D-ring, like me, or another location?

 

[formernuke]

It's silly to use both and defies logic. Some divers love to clip every piece of equipment they own on to themselves. Even instructors.

Next time ask him why he recommends both.

Transmitter on right post spg on left, that way if I have to isolate I have pressure in both tanks.

For a shallow dive I pulled my spg off because my buddies went boom, allowed him to still do the dive.