Question Bigger tanks, dive times and SI’s in Coz

[Saboteur]

Hi all. In looking at dive ops, many offer larger tanks and/or advertise long dive times. All of my tropical diving has been on TCI or GC with use of 80 cf tanks, and usually 1 hr or less dive times. Some ops I found liked to really push to get back for the afternoon dives and hastened the SI - which of course affected the second dive. Or they seemed in a hurry to get back to the marina and clean the boat. The ”surface with 500 psi“ parameter seemed to mean 500 or 60 minutes. Occasionally you could sense the annoyance in the crew if you pushed the dive time being last to surface.

Do these dive ops really let you dive as long as you want within gas and NDL limits - even with larger tanks? Thanks

 

[morecowbells]

We quit using a dive op that a) did not allow you to dive your computer b) rushed surface intervals. Read the fine print in finding ones that let you dive your computer time/profile. I am a cheerleader for Bottom Time Divers. No group ascents or time limits. Just stay within non deco limits. SI's are a firm hour. As for large tanks, I think any dive op can arrange for you to use one, provided you give a heads up.

 

[ReefHound]

There must be a hundred dive ops on Coz so if you don't like how one op manages dive times and surface intervals just find another one. In general, the "cattle" boats are going to be stricter on dive times and impose 60 minutes max, perhaps 40-45 minutes. It takes them longer to transit dive sites and get people in and out of the water. That time has to be made up somehow. I've never been barked at for going a bit over 60 minutes with a smaller boat and often go 70-75 minutes.

Most ops I've seen practice a one hour surface interval. There's nothing magic about one hour. You don't go from unsafe at 55 minutes to perfectly safe at 65 minutes. Off-gassing is continuous and the more time on surface the more you will offgas and the more bottom time you'll have on the next dive. Three hours would be even better but would bore most people to death and wreak havoc on dive schedules. One hour is a nice round time interval that balances off-gassing with scheduling.

 

[yle]

One important factor in getting long dive times and a nice long SI (so you can have a decent NDL for the second dive) is everyone having their act together in the morning so the boat can leave on time. Of course the fewer divers on the boat, the less likely there will be problems that will delay the boat leaving.

If everyone is ready to go at the time the dive op specifies and there are no delays due to technical problems, the boat can get out on time and everyone will be more likely to get that one hour in, one hour out, one hour in, without the need to rush back to the marina.

Our last trip to Coz went just this way... every morning for a week we had an hour-long pair of dives (with AL80's) with an easy hour in between. Our boat had 8 to 10 divers each morning.

 

[Saboteur]

There must be a hundred dive ops on Coz so if you don't like how one op manages dive times and surface intervals just find another one. In general, the "cattle" boats are going to be stricter on dive times and impose 60 minutes max, perhaps 40-45 minutes. It takes them longer to transit dive sites and get people in and out of the water. That time has to be made up somehow. I've never been barked at for going a bit over 60 minutes with a smaller boat and often go 70-75 minutes.

Most ops I've seen practice a one hour surface interval. There's nothing magic about one hour. You don't go from unsafe at 55 minutes to perfectly safe at 65 minutes. Off-gassing is continuous and the more time on surface the more you will offgas and the more bottom time you'll have on the next dive. Three hours would be even better but would bore most people to death and wreak havoc on dive schedules. One hour is a nice round time interval that balances off-gassing with scheduling.

Yep agree. But I don’t like being hustled when DM’s have been rounding up people and getting some in the water less than a hour.

 

[Curious_George]

Hard to have a thread on large tanks at Cozumel without mentioning Aldora and their HP120’s.

Some will point out that they typically surface as a group, but with 4-6 people max, and relatively experienced divers, most usually are ready to surface about the same time or can manage their depth to extend the dive if needed. And I have seen people surface two at a time with them.

Looking at my last trip with Aldora, almost half the dives were 1.5 hrs and the 1 hr dives had significant time at 100’+. 32% first dive, 1.5hr surface interval and 36% second dive was pretty much mandatory to stay out of deco.

 

[NDL_Diver]

Hard to have a thread on large tanks at Cozumel without mentioning Aldora and their HP120’s.

Some will point out that they typically surface as a group, but with 4-6 people max, and relatively experienced divers, most usually are ready to surface about the same time or can manage their depth to extend the dive if needed. And I have seen people surface two at a time with them.

Looking at my last trip with Aldora, almost half the dives were 1.5 hrs and the 1 hr dives had significant time at 100’+. 32% first dive, 1.5hr surface interval and 36% second dive was pretty much mandatory to stay out of deco.

Yep, most of our dives with Aldora (nitrox is must) is a 75min dive at 100' max 1st dive (32%) and 90 min (occasional 100+ with a really the good group) second dive at 70' max (36%). Surface Interval is at beach club and is enough to eat lunch, hit the bathroom.... never rushed but in the 90 min range. Their 120CF tanks are always filled to proper starting pressure.

Air boats run different profile (less time at depth before sawtooth up to shallower depth reef). The DM does a good job moving up the reef as blood nitrogen levels increase. The don't mix air divers with nitrox divers unless nitrox divers request.

 

[NDL_Diver]

The 1st day (checkout) the evaluate your air consumption and on day 2 you may be on a different boat with more like (air consumption) divers.

 

[ggunn]

The 1st day (checkout) the evaluate your air consumption and on day 2 you may be on a different boat with more like (air consumption) divers.

The evaluation during the first dive(s) is generally a practice with most Cozumel dive ops that don't already know you.

 

[drrich2]

In looking at dive ops, many offer larger tanks and/or advertise long dive times.

You may already know this, but the added clarity may help newer divers considering a Cozumel trip who run across this thread.

100-cf AL Tanks are widely available on Cozumel from what I understand; I had them on a trip diving with Tres Pelicanos (had a great trip with them). But they hold 100-cf at a rated fill pressure of 3,300 PSI; the actual fill pressure is apt to be close to 3,000 PSI, so the actual gas volume for your dive is closer to 90-cf. Still a meaningful increase over an 80-cf tank, but good to know.

A few op.s offer steel 120-cf tanks. Living Underwater (with whom I did 2 dives on a cruise stop years ago, was quite happy with and recommend) had low pressure 120's; I've heard Aldora has high pressure 120's. I heard of another op. with 120's, for but whatever they don't seem to get mentioned on ScubaBoard for that quite as much as Living Underwater and Aldora.

When I planned my trip, I was torn between Tres Pelicanos and Aldora. I figured I was looking at 4 dives/day with TP, 3 longer dives with Aldora, and there'd be less hassle getting in and out of the water with Aldora but I might hit more dive sites with TP (due to more dives).

My point is, you might consider whether you'd like 4 near hour long dives/day, or a similar amount of dive time in 3 longer dives/day. Not sure just how the math works out. If I went back, I'd check whether Aldora would get me done diving and home a little earlier in the day. I loved diving with TP, but I hit the bed exhausted.