Kona Konundrum

[LeadTurn_SD]

Not at all. You should love physics totally. Going from sea level to 1600 feet above sea level is a pressure swing of 2 feet of sea water (a pressure drop of 5.6%). Do you think a 2 foot difference in a dive would be decisive in determining if you get bent on a dive? And the manta dives are in what like 25 fsw? You could dive forever in 25 fsw and your risk of getting bent short of shooting to to the surface and getting AGE would be close to zero. It would be more risky to do your dive at 30 fsw than to drive to Hilo a few hours later. Do your dive in Kona, clean up, go to lunch, and then drive over to Volcano National Park. Your risk is very low.

Mr. C,

I generally agree with the above, with the exception of the drive through Volcano.

The main highway crests 4,000+ feet I think (or maybe 4,500??). I should remember the exact height, but do not

The risk is still low, but my opinion is that you do need to exercise some caution and refer to the tables if you are planning on ascending that high anytime soon after the dive(s). By soon I mean within just a couple - few hours.

While many single, shallow reef, no-stop dive profiles with an AL80 probably would not require a much or any surface interval before being cleared by the NOAA tables to ascend to 4,000 feet, it is still possible.... But after a two-tank morning, you'll probably have enough nitrogen load to warrant some caution... again, I've run numbers on two-tank dive profiles I typically do (with single Al80's), and for safety simply use the "5 hour" rule for myself and my family.... and still avoid driving Volcano for added safety. This may be overly conservative... but it is easy enough to find enough "stuff" to do to kill that much time before driving back to Hilo in the late afternoon.

The dive ops will often advise following the DAN "Time To Fly" guidelines, which are too conservative I think, but they have liability concerns.

Best wishes.

 

[friscuba]

Assuming I'm running the NOAA tables correctly, you're looking at 7 hour and 26 minutes before driving the highway to volcano (pretty sure it's over 4000 feet, I think the 4500 foot mark is pretty close) via the southern route after two 40 foot dives for 50 minutes with a surface interval of an hour. That's pretty conservative diving. At 40', I'd be doing about 80 minutes if I'm not trying to conserve air, the NOAA tables (again if I'm doing them correctly) have that as nearly a 12 hour wait to go between 4 and 5K in elevation.

I prefer to err on the side of caution qwhen it comes to DCS risks.

 

[Quero]

Just as a bit of trivia... Highway 11 tops out at 4032 feet at Volcano (about mile 92). The drive from the west (Kailua) dips to its minimum altitude of 92 feet at Whittington Beach Park (about mile 61). So in just 31 miles, the altitude change is over 3900 feet.

 

[acooper]

Another Kona area diver here, actually a bit north, Puako and Kawaihae. We regularly dive and drive home to 1k, many of our dive buddies live in Waimea, at 2,800ft, the high point in the northern route around the island. The normal routine is a morning dive or two, followed by a leisurely lunch in Kawaihae to de-gas before heading home. Never a problem.

Caution is never a bad idea in diving, but some of the published tables are a bit overcautious. Remember we are dealing with exponential functions here. Most of the N will be out of your tissues in the first few hours of being on the surface. Likewise, atmospheric pressure (unlike underwater pressures) follows an exponential. The first few thousand feet do not make a lot of difference, but the change increases rapidly as you continue to climb. Saddle Road? Probably not, 6,800ft at the top of the saddle. Waimea? Just do not drive straight there after getting out of the water. Kona and Kohala have a lot of nice places to kick back for a few hours before you go.

 

[Pliny]

Caution is never a bad idea in diving, but some of the published tables are a bit overcautious. Remember we are dealing with exponential functions here. Most of the N will be out of your tissues in the first few hours of being on the surface. Likewise, atmospheric pressure (unlike underwater pressures) follows an exponential. The first few thousand feet do not make a lot of difference, but the change increases rapidly as you continue to climb. Saddle Road? Probably not, 6,800ft at the top of the saddle. Waimea? Just do not drive straight there after getting out of the water. Kona and Kohala have a lot of nice places to kick back for a few hours before you go.

Atmospheric pressure decreases fastest as a function of altitude gain at sea level.

You also have to think about your profile. If you have a short deep profile to the NDL then then controlling compartment is fast and you will degas fast. If you do a long shallow dive then the controlling compartment is slow and you will take longer to get to a point where you can ascent to altitude.

That said, the manta dive is shallow and short-ish.

 

[BSOD]

FWIW, I dove Kona 4 days in a row (4 tanks the first day, then 2 tanks the next three days), then drove up to Waimea a bit over 24 hours after my last dive, and started to feel a little tingly in my joints and muscles as I was getting nearer/higher. After a while of still feeling progressively tingly, I made a U turn and headed back down to be on the safe side (and then the tingling went away). Maybe it was just in my head, not drinkin enough, and/or more likely the number of dives, but thought I'd throw that out there, since everybody else is saying it's no biggie, and it probably really is if just doin 2 tanks.

If it fits your schedule, maybe visit the higher elevation places first, then do your dives?