Computers and backups - looking for pearls of wisdom from the more experienced

[Hoag]

Backup computer is pointless for rec diving. The point of rec diving is you’re never under a deco ceiling: anything goes wrong you can ascend anytime. Safety stop is nice but it’s not a real deco stop, you can blow it off and still be “safe-ish”; that describes all of diving anyway. It’s a good idea to have a backup computer on any big trip but it lives in your save-a-dive kit with your o-rings and wrenches, it doesn’t normally get wet.

Redundancy is great for the things that keep you alive, sure. With serious tec diving with serious deco the computer qualifies, sure. There are still plenty of things that will kill you at 20’-45’ (or 20”-45”) but computer failure just isn’t one of them.

You won’t go far wrong with a AI Perdix as your primary computer though. You might not ever use its trimix or rebreather modes but the big bright screen, good controls, and bulletproof reliability will serve you every dive. That’s what I’ve got and I’m very happy with it.

You say that a backup computer is pointless for rec diving. I wholeheartedly disagree. Having redundancy is never pointless. It might not be absolutely essential, but it is never pointless. There is an old saying in the RCAF that one is zero and two is one when something fails.

I was on a LOB once and my computer died on a dive. The screen went blank and nothing would bring it back. I aborted that dive and if I was not able to borrow a computer from the boat for the rest of the week, I would have become a passenger, not a diver. That was the last trip I have done without a backup dive computer.

 

[nanohawk]

You say that a backup computer is pointless for rec diving. I wholeheartedly disagree. Having redundancy is never pointless. It might not be absolutely essential, but it is never pointless. There is an old saying in the RCAF that one is zero and two is one when something fails.
I was on a LOB once and my computer died on a dive. The screen went blank and nothing would bring it back. I aborted that dive and if I was not able to borrow a computer from the boat for the rest of the week, I would have become a passenger, not a diver. That was the last trip I have done without a backup dive computer.

Exactly. Some folks may not have the budget to buy the redundancy on their dive trip. I respect that. As with many things you can spend time or money. If you don't have money, you usually spend time. If you have the money, you can reduce the cost in time.

In this case, for NDL recreational diving on trips, the money spent reduces the likelihood of having to sit out for one or more days due to a computer glitch or failure.

I probably will pick up another used Perdix AI without the transmitter as a backup. Not the least expensive way to go. Diving, Private Airplanes, and Boats are not the 3 cheapest hobbies in the universe.

A boat is a hole in the water that you throw money at. B.O.A.T. = Bring Out Another Thousand. Diving is hand-delivering that money to the water.

 

[rhwestfall]

Risk/reward management... What is the value of sitting out? Sometimes nothing, other times much. Only you can decide the value of sitting out the dive(s)....

 

[nanohawk]

Risk/reward management... What is the value of sitting out? Sometimes nothing, other times much. Only you can decide the value of sitting out the dive(s)....

Somewhere around North of $500 USD / day on a typical week long trip with 5 days of diving. Depending on where you are going and the cost of getting there it might be more or less.

 

[boulderjohn]

In my experience, the SIs in Cozumel have been relatively long. My last trip with Aldora had an average SI of 1:40. On the other hand, my SIs in SE FL probably average about 45 min, sometimes as short as a half hour. Of course, it depends on your next dive. I nearly always use my NDL planner to ensure I have enough bottom time. I'm sure these habits are geographical, yours are likely quite different.

Because Aldora uses primarily steel HP 120 cylinders, its dives tend to be very long, often around 80 minutes. They have to have a long surface interval in order to allow for a decent second dive. If you are doing shorter dives, you can have shorter surface intervals.

 

[Blackcrusader]

In NDL diving, the GF low number does not matter. The GF high number is all you have to worry about. If you use a Shearwater, it has a feature called SurfGF, which is a very nice way of telling you what your GF would be if you surfaced right then. When I am doing NDL dives, I use that to tell me when to end my safety stop most of the time, except when I am with friends and have to wait for them to count off their 3 minutes.

Yup in my NDL diving I normally spend the last 10 minutes at 5m on reefs or taking photos before ascending to get on the boat or ending a shore dive. Often times dive guides like to keep vacation divers shallow towards the end of the dive so divers actually dont even realize they are really diving at the safety stop level to finish of the dive. There are dives where we are say still at 10m depth then need to ascend to the safety stop. I remind guides before starting the dive I have set my Perdix to 5 minutes not 3.

As to RDP tables I agree that they are not the best for multilevel diving over a series of dives like I do. 45 plus dives in 12 - 14 straight days of diving I rely on my Perdix.

 

[Blackcrusader]

I don't fully trust the strap. To put it another way I would not use that strap to secure a $1,000 USD bill. If it comes loose it will do so at an inopportune time where the computer will never be seen again.

I have done several hundred dives using the straps. Never had an issue and there are two of them not one. The likely hood of losing the Perdix on a dive without losing the arm it's on is pretty low imho.

 

[Blackcrusader]

I’d rather have the abacus, two even.

These are the Sharewater backup analogue dive computers to go along with your tables. A rec and a tech version. Batteries not required.

 

[Blackcrusader]

I thought he had a great presentation. His video came up when I was looking for something that explained the difference between bubble and gas tissue models. While I realize the info isn't directly applicable to NDL I still found it interesting and informative.

SurfGF sounds like a great feature. I will look it up when I get the computer out of the box and start setting it up.

Take your time to read the manual. There is a lot of reading to be done and I did so several times. Also learn how to setup what features you want on your screen. It does take time to really learn the Perdix or for me it was after using the Suunto. By the way I dive using the Tec mode not the Rec mode. So you also need to study the two different modes.

 

[nanohawk]

I have done several hundred dives using the straps. Never had an issue and there are two of them not one. The likely hood of losing the Perdix on a dive without losing the arm it's on is pretty low imho.

I was referring to the Suunto's single strap.