Blue Hole Dive Planning

[ScubaSloan]

I am counting the days until I arrive in Belize (22) and have been reading through the boards and something has continually caught my eye: the profile on the Blue Hole dive. Let me start out by saying, I plan to sit this dive out due to the fact that, while I have my deep specialty and a handful of dives at 100 feet, I have only about 25 dives in my short diving career and I have never been to 130 and would rather work up to it. That aside, I have not been able to get comfortable with the dive plan if I were to do it in the future.

This is the dive plan that I have seen:
On an AL80
3 min to descend (40 ft/min)
8 min of bottom time (doesn't this already put you past your NDL when including your descent?)
3 min ascent to a 1 minute stop at 40 ft
1 min ascent to a 5 minute stop at 15 ft
ascent to surface

I know there are variations on this profile, but I believe they all end up about the same place (unless time at 130 is limited).

My air calculations are below in the format Time * ATA * RMV = CuFt air used. My assumed RMV on an AL80 is 0.65.
I assumed a second diver on ascent sharing my air.

Descent: 3*2.97*0.65=5.83
Bottom: 8*4.94*0.65=25.68
Ascent to deep stop: 3*3.58*0.65 *2=14.03
Deep stop: 1*2.21*0.65*2=2.90
Ascent to safety stop: 1*1.83*0.65*2=2.4
Safety stop: 5*1.45*0.65*2=9.5
Ascent to surface: 1*1.23*0.65*2=1.6
Total Cuft Air Used: 62.10 (2407 PSI used, 592 remaining)

And this is if everything goes well, this does not plan for a stressed diver with the second air user.

Am I missing something. My math, my profile? I know my SAC is not great at around 25, but is that really all it is? It seems that this is cutting it pretty close.

Thoughts from those that have dove the blue hole or just have an opinion? Anyone else have a similar sentiment when they went to the Blue Hole (decided to snorkel it)?

Thanks,

Sloan

 

[mlevi98]

Sloan:
I have done this dive twice, each time with different operators, Amigos and Aqua Dive. Both operators were very clear that the most time we would spend at depth would be 5 minutes or less. The actual profile from my computer for my second dive with Aqua Dives was:

8 min descent
4 min @ max depth 132-139ft
10 min ascent to 20ft
6 min stop @ 20'
1 min ascent to surface
27 minutes total
The computer recorded 4 minutes of required decompression @ 10ft as I passed from 115 to 77ft on the ascent over 3 minutes.

This is a dive that exceeds NDC limits but falls well within the range of safety.
On both trips there were two dive masters with our group, one in the lead and one at the rear. They also hung a spare tank from the boat for use in an emergency.

Although I have 50 or so logged dives and prior to the Blue Hole none were beyond 100ft. I don't dive very regularly and I still exited the water with at least 1000psi remaining. Now having said, that I made sure I did at least a day or two of diving before I went to the Blue Hole each time so that I was comfortable with my equipment and buoyancy control. It is a unique dive site and experience, there are many sharks (at least 10 on each dive) to see and tons of giant grouper. If you are comfortable with your dive skills then I recommend doing the dive.

I hope this is helpful.
-Michael

 

[peterbj7]

A couple of points. "Bottom time" includes descent time, so 8 mins bottom time in your case means 5 mins at the bottom. Your profile above undoubtedly puts you into deco (I haven't calculated it) so there's that to consider in planning your ascent.

And your RMV is certainly rather high. I think mine is somewhere around half that.

The normal "bounce" dive in the BH is done strictly as a group dive, so you needn't anticipate having someone sharing your air. There are DMs for that.

The shelf that most people dive to is at 150ft, though many people dive without a depth gauge (!!!) so have no idea what depth they went to. I've heard a DM say with a straight face that the dive went to 130ft with bottom time of 8mins so could not have gone into deco, when actually they went to 150ft and their time at the bottom was about 8mins (so Bottom Time was significantly more) and they were well into deco - had they but known. I was criticised by a boat captain once when I just went down for the dive, watching but not interfering, and had several minutes' deco on my two computers when I got back up.

But have no fears over safety. It's a closely monitored dive and you won't be allowed to get into trouble. As a recreational bounce dive I don't particularly rate it (I've done it much more comprehensively) but it's still quite an experience for an early diver. Do it.

 

[atedeschi]

Here is a Vplanner profile, you are not in deco for a 8min BT to 130' on air.

Dec to 130ft (2) Air 50ft/min descent.
Level 130ft 5:24 (8) Air 1.04 ppO2, 130ft ead
Surface (12) Air -30ft/min ascent.

OTU's this dive: 10
CNS Total: 3.4%

33.0 cu ft Air
33 cu ft TOTAL

9min is your max before u hit deco.

here is a 150' on air with 6min BT

Dec to 150ft (3) Air 50ft/min descent.
Level 150ft 3:00 (6) Air 1.16 ppO2, 150ft ead
Surface (11) Air -30ft/min ascent.

OTU's this dive: 9
CNS Total: 3.4%

29.9 cu ft Air
29.9 cu ft TOTAL

 

[ScubaSloan]

Peter, I agree with the descent + bottom time, the resort where I will be diving said 3-5 min descent, 8 min bottom time, so I took that to mean in addition to. If that is in fact the case, I feel much better with the profile. Thanks for your reply.

 

[Darnold9999]

While I am not a fan of this dive - highly overrated - if you are there and comfortable with your skills do the dive. If you don't do it you will wonder what you missed.

You want to do a few dives before this one to make sure you are comfortable, but it is a pretty simple dive. Go down deep, look around for a minute or two and head back up. A been there done that kind of dive. Not particularly interesting IMHO.

 

[ApexLongimanus]

While I am not a fan of this dive - highly overrated - if you are there and comfortable with your skills do the dive. If you don't do it you will wonder what you missed.

You want to do a few dives before this one to make sure you are comfortable, but it is a pretty simple dive. Go down deep, look around for a minute or two and head back up. A been there done that kind of dive. Not particularly interesting IMHO.

100% agree. on all points.

 

[Damselfish]

While I am not a fan of this dive - highly overrated - if you are there and comfortable with your skills do the dive. If you don't do it you will wonder what you missed.

You want to do a few dives before this one to make sure you are comfortable, but it is a pretty simple dive. Go down deep, look around for a minute or two and head back up. A been there done that kind of dive. Not particularly interesting IMHO.

yes, I think this is a perfect summary.

 

[scubafanatic]

...what's hilarious about Belize/Blue Hole is that whenever I see an article/magazine advertisement/article it usually features a grandiose aerial shot of the 'famous Blue Hole'...like it's the centerpiece of the Belize diving experience and the justification for planning a trip there....but somehow the 5 min of bottom time doesn't get mentioned !

 

[Ayisha]

I agree that the Blue Hole is a been there, done that dive. You want to do it once to see what all the fuss is about, but it may not be something that attracts you on future visits to Belize. We were lucky to see lots of huge reef and lemon sharks, and apparently one bull shark, and lots of huge grouper, but it was very silty down there. The viz was about 30 feet in the Blue Hole and it was tough to take pictures.

One thing I would like to add is that when I did the Blue Hole with Aqua Dives, we did not do it as a square profile, which is what seems to be the case with many of the above posts. We did it as a multi-level dive, which is a much safer profile. I did not actually download the dive profile from my computer, but it was something like this. We dropped as quickly as possible to about 135 feet, stayed there for a few minutes and looked around, then went slowly to about 50 feet and stayed there for several minutes, then went slowly to about 20 feet and stayed there for 5 - 8 minutes. My computer never went into deco and I came back with my 63 cf tank half full. My total dive time was 24 minutes.