Question Should I replace my SPG with my new Shearwater Transmitter?

[Divin'Papaw]

It that a Dive Rite XT1 or an FT1 first stage? I'm looking at my FT1 on my desk and I very much doubt the Swift would be able to attach without clashing with the LP hoses

XT1

 

[boqurant]

XT1

Okay cool yeah. I also have an XT1 on my desk and that does look like it would allow direct mount

 

[boqurant]

FWIW I'll chime in with a barely-qualifed opinion, and hopefully be able to update this in the long future.

A little while and +22 dives later, I've decided to keep the SPG + AI combo, with the AI transmitter mounted over my right shoulder (on 6" HP hose), and the SPG on my left side where it belongs, clipped off to the left waist D-ring.

I realise now that the opposite way around was just silly: I didn't like 3 big hoses emerging on the right, and the SPG hose offered a tangle hazard for my 2nd stage primary hose. So it's back to the more conventional way around!

I've also read through tonnes of posts here about whether to use SPG, AI or both and came to my own conclusions based on (an uneducated attempt at) some logic. In case it helps anyone I'll note it below.

The upshot (for me) is going AI-only gives very minor benefits, whilst introducing slightly less minor (although still small) risks and irritations - which are particuarly felt on expensive liveaboard trips where I want to avoid having to call any dives.

Issue	(A) SPG Only	(B) AI Only	(C) SPG+AI
1. Computer failure / loss	Require buddy (read his depth, monitor own SPG). Optional abort together (safety stop)	Require buddy (read his depth, guess own air). Conservative**: Mandatory abort together (safety stop if I can guess air).	Require buddy (read his depth, monitor own SPG or AI). Optional abort together (safety stop)
2. SPG bad reading (e.g. stuck needle)	Can handle alone. Mandatory abort (safety stop if I can guess air)	N/A	Potentially ignore. Can handle alone. Optional abort (safety stop)
3. SPG HP leak	Can handle alone. Mandatory abort (safety stop if I can guess air)	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)
4. AI bad reading (e.g. no TX or battery)	N/A	Can handle alone. Conservative**: Mandatory abort (safety stop if I can guess air)	Potentially ignore. Can handle alone. Optional abort (safety stop)
5. AI HP leak	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)	Can handle alone. Mandatory abort (safety stop if I can guess air)
6. SPG bad reading and AI bad reading (very unlikely)	N/A	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)
Total aborts	2 Mandatory 1 Optional	** If Conservative 3 Mandatory 0 Optional ** else, iff I have a good mental note of GTR and SAC/RMV, then: 1 Mandatory 2 Optional (but still likely to call a little early for safety margin)	2 Mandatory 1 Optional 2 Potentially ignore 1 (very unlikely) Mandatory
Net aborts vs A	N/A	** If conservative +1 Mandatory -1 Optional ** else: -1 Mandatory +1 Optional	+2 Potentially ignore +1 (very unlikely) Mandatory

Decision to resolve / make peace with moving from A -->B vs from A --> C​

• Assume Conservative, is (B) +1 Mandatory worse than (C) +2 Potential Ignore +1 Very Unlikely Mandatory ?
• Assume Conservative, in particular (B) forces a computer failure / loss to be a mandatory abort rather than in (C) an optional abort. Still need buddy either way to read his depth. It's always nicer to avoid having to call a dive if it's a good one in a hard-to-reach expensive location!

Various Operational Pros / Cons of B​

• Pros: Leaner reg set; better in-water profile; less equipment for deckhands to damage; fewer o-ring failure points
• Cons: Still have to bring SPG on liveaboards as a backup so packing is not lighter; have to get competent at fitting an SPG to my 1st stage; slightly more annoying tank-fill checks

 

[Divin'Papaw]

A little while and +22 dives later, I've decided to keep the SPG + AI combo, with the AI transmitter mounted over my right shoulder (on 6" HP hose), and the SPG on my left side where it belongs, clipped off to the left waist D-ring.

I realise now that the opposite way around was just silly: I didn't like 3 big hoses emerging on the right, and the SPG hose offered a tangle hazard for my 2nd stage primary hose. So it's back to the more conventional way around!

I've also read through tonnes of posts here about whether to use SPG, AI or both and came to my own conclusions based on (an uneducated attempt at) some logic. In case it helps anyone I'll note it below.

The upshot (for me) is going AI-only gives very minor benefits, whilst introducing slightly less minor (although still small) risks and irritations - which are particuarly felt on expensive liveaboard trips where I want to avoid having to call any dives.

Issue	(A) SPG Only	(B) AI Only	(C) SPG+AI
1. Computer failure / loss	Require buddy (read his depth, monitor own SPG). Optional abort together (safety stop)	Require buddy (read his depth, guess own air). Mandatory abort together (safety stop if I can guess air)	Require buddy (read his depth, monitor own SPG or AI). Optional abort together (safety stop)
2. SPG bad reading (e.g. stuck needle)	Can handle alone. Mandatory abort (safety stop if I can guess air)	N/A	Potentially ignore. Can handle alone. Optional abort (safety stop)
3. SPG HP leak	Can handle alone. Mandatory abort (safety stop if I can guess air)	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)
4. AI bad reading (e.g. no TX or battery)	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)	Potentially ignore. Can handle alone. Optional abort (safety stop)
5. AI HP leak	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)	Can handle alone. Mandatory abort (safety stop if I can guess air)
6. SPG bad reading and AI bad reading (very unlikely)	N/A	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)
Total aborts	2 Mandatory 1 Optional	3 Mandatory 0 Optional	2 Mandatory 1 Optional 2 Potentially ignore 1 (very unlikely) Mandatory
Net aborts vs A	N/A	+1 Mandatory -1 Optional	+2 Potentially ignore +1 (very unlikely) Mandatory

Decision to resolve / make peace with moving from A -->B vs from A --> C​

• Is (B) +1 Mandatory worse than (C) +2 Potential Ignore +1 Very Unlikely Mandatory ?
• In particular (B) forces a computer failure to be a mandatory abort rather than in (C) an optional abort. Still need buddy either way to read his depth. Chances of computer failure / loss?

Various Operational Pros / Cons of B​

• Pros: Leaner reg set; better in-water profile; less equipment for deckhands to damage; fewer o-ring failure points
• Cons: Still have to bring SPG on liveaboards as a backup so packing is not lighter; have to get competent at fitting an SPG to my 1st stage; slightly more annoying tank-fill checks

Sound and thorough logic. I do question some of your mandatory aborts. For example, why would losing Tx mid-dive by default require mandatory abort (Col. B/Line 4)? Do you not have a decent sense of your air consumption and how much air you should have at that point? Just something to ponder. I dive AI only (but am certainly open to those that chose not to). IF I were to lose my AI Tx mid-dive, I would certainly be conservative and probably cut the dive a bit short, but I would not view it as an immediate abort. After all, I should have plenty of gas in my tank at that point being delivered to me to breath. The only issue is that I don't know EXACTLY how much gas I have left, thus cutting the dive a bit short. But I have a strong sense of my air consumption and would be able to conservatively estimate how much time I have left based upon what my pressure was when I lost Tx.

I applaud your thorough analysis and reasoning. Bottom line ... if diving with both an AI and SPG works best for you and makes you most comfortable, by all means do so!

 

[boqurant]

For example, why would losing Tx mid-dive by default require mandatory abort (Col. B/Line 4)? Do you not have a decent sense of your air consumption and how much air you should have at that point?

Thanks for checking my logic, I perhaps got into the weeds too much and started questioning myself!

That's a very good point regarding B1 & B4 and you're right: on my most recent dives with AI I really enjoyed being able to monitor my tank pressure (and various goodies including GTR, SAC) on a constant basis, and I did have it in my head most of the time too. I'll update the table.

That said, my main sticking point I think is computer failure / loss, which (if conservative) would be a mandatory abort on the dive. Also any subsequent dives on a liveaboard trip would also require me to fit the SPG, and although I have a spanner, o-rings and silicon grease in the SAD kit, I'm not sure how much I trust my lack of experience to get that right!

 

[OMyMyOHellYes]

A little while and +22 dives later, I've decided to keep the SPG + AI combo, with the AI transmitter mounted over my right shoulder (on 6" HP hose), and the SPG on my left side where it belongs, clipped off to the left waist D-ring.

I realise now that the opposite way around was just silly: I didn't like 3 big hoses emerging on the right, and the SPG hose offered a tangle hazard for my 2nd stage primary hose. So it's back to the more conventional way around!

I've also read through tonnes of posts here about whether to use SPG, AI or both and came to my own conclusions based on (an uneducated attempt at) some logic. In case it helps anyone I'll note it below.

The upshot (for me) is going AI-only gives very minor benefits, whilst introducing slightly less minor (although still small) risks and irritations - which are particuarly felt on expensive liveaboard trips where I want to avoid having to call any dives.

Issue	(A) SPG Only	(B) AI Only	(C) SPG+AI
1. Computer failure / loss	Require buddy (read his depth, monitor own SPG). Optional abort together (safety stop)	Require buddy (read his depth, guess own air). Mandatory abort together (safety stop if I can guess air)	Require buddy (read his depth, monitor own SPG or AI). Optional abort together (safety stop)
2. SPG bad reading (e.g. stuck needle)	Can handle alone. Mandatory abort (safety stop if I can guess air)	N/A	Potentially ignore. Can handle alone. Optional abort (safety stop)
3. SPG HP leak	Can handle alone. Mandatory abort (safety stop if I can guess air)	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)
4. AI bad reading (e.g. no TX or battery)	N/A	Can handle alone. Likely mandatory abort to be conservative, but optional in the case that I have a good mental note of GTR and SAC/RMV (safety stop if I can guess air)	Potentially ignore. Can handle alone. Optional abort (safety stop)
5. AI HP leak	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)	Can handle alone. Mandatory abort (safety stop if I can guess air)
6. SPG bad reading and AI bad reading (very unlikely)	N/A	N/A	Can handle alone. Mandatory abort (safety stop if I can guess air)
Total aborts	2 Mandatory 1 Optional	3 Mandatory 0 Optional	2 Mandatory 1 Optional 2 Potentially ignore 1 (very unlikely) Mandatory
Net aborts vs A	N/A	+1 Mandatory -1 Optional	+2 Potentially ignore +1 (very unlikely) Mandatory

Decision to resolve / make peace with moving from A -->B vs from A --> C​

• Is (B) +1 Mandatory worse than (C) +2 Potential Ignore +1 Very Unlikely Mandatory ?
• In particular (B) forces a computer failure / loss to be a mandatory abort rather than in (C) an optional abort. Still need buddy either way to read his depth. It's always nicer to avoid having to call a dive if it's a good one in a hard-to-reach expensive location!

Various Operational Pros / Cons of B​

• Pros: Leaner reg set; better in-water profile; less equipment for deckhands to damage; fewer o-ring failure points
• Cons: Still have to bring SPG on liveaboards as a backup so packing is not lighter; have to get competent at fitting an SPG to my 1st stage; slightly more annoying tank-fill checks

If you wear two computers, and your tank has two transmitters and your pony has its own compact SPG ... Oh, and a spare mask, and by virtue of the two computers, two compasses, and carrying two cutters, 4 surf level signaling devices (DSMB, mirror, Whistle, Nautilus )? But no mechanical SPG on the primary single tank? What then?

 

[boqurant]

Damn, I knew there was something I was forgetting