Is Diver Alert (Whistle on LP inflator) DIR?

[ivobj]

Don't hire a boat guy unless he has really big ears.

Big and functional...hehe, size is not always proof of effeiciency!!

 

[miketsp]

..snip..
Sound is attentuated at the cube of distance and considering most diesels are ~65db it doesn't take much distance, or waves for a dive alert's signal to attentuate. ..snip..

Just curious where you picked up this piece of misinformation.

It doesn't fit in with any the accepted exponential decay formulae and it doesn't take into account that there will be significant ground (=sea) reflectance and it doesn't take into account the fact that a Dive Alert is not an omnidirectional radiator but is in fact quite directional on an axis running through the horn.

 

[b1gcountry]

From Wikipedia:

* Frequency and Distance – Sound pressure level decreases by half (six decibels) with each doubling of distance due to divergence from the source. This relationship is termed inverse proportional, often incorrectly described as the inverse square law; the latter applies to sound intensity, not sound pressure. Sound pressure level also decreases due to atmospheric absorption, which is strongly dependent upon frequency, lower frequencies traveling farthest. For example, a 1000 Hz whistle has an atmospheric attenuation coefficient one half that of a 2000 Hz whistle (calculated for 50 percent relative humidity at 20 degrees Celsius). This means that in addition to divergent sound dampening, there would be a loss of 0.5 decibel per 100 meters from the 1000 Hz whistle and 1.0 decibel per 100 meters for the 2000 Hz whistle. Additional factors affecting sound propagation include barriers, atmospheric temperature gradients, and "ground effects.”

Also, note that Db are measures in a logarithmic scale.

Tom

 

[b1gcountry]

Then why use a bottom timer? Can't DIR divers count?

"1 Mississippi, 2 Mississippi, 3 Mississippi..."

If you need redundant timers, do you have to count:
"1 Mississippi, 1 Mississippi, 2 Mississippi, 2 Mississippi, 3 Mississippi..."

 

[RTodd]

The air horn thingy isn't DIR because it is a crutch for proper skills and dive planning. Leaving out some really crazy unrealistic scenarios, you are going to get seperated from a boat for generally two reasons. Your navigation sucks or it is a drift dive and you haven't properly planned to stay in contact with the boat. For option 1, stay closer to the boat until you can make it back to the anchor. For issue 2, there are several great DIR ways for dealing with this and it doesn't take a fully compliant DIR boat to do it. Both of these issues are fixable before you leave the doc and therefore don't require an unnecessary whistle.

While you don't need a DIR boat, a complete stroke mess of a boat is a no-no for drift diving. In most cases the whole boat basically has to dive together and you use a float ball or shoot a bag for deco, depending on the conditions, type of dive, etc.

 

[MXGratefulDiver]

Wow ... I get the impression some of y'all don't dive in current very often.

They call 'em "predictions" for a reason ...

Maybe I don't understand DIR either ... because my understanding of it is that what you take with you depends on the conditions you anticipate diving in. You balance the benefit of the gear against the potential downside of not having it and decide accordingly.

If I'm diving someplace where currents are known to be quirky, I'm taking both a bag and an audible signaling device. As RJack suggested, I'd clip it off in my pocket ... but I'd definitely take it with me. Relying on the boat captain can lead to uncertain results. I've dived in places where the currents are takign divers in opposite directions within 20 feet of each other (Campbell River/Quadra Island). You get two teams shooting bags in conditions like that and the captain's gonna have to decide which one to follow. I've also dived in places (Neah Bay comes immediately to mind) where fog and waves can roll in within a very short time period ... certainly less than the length of a typical dive. If that happens while you're down, even a DIR captain's gonna have trouble seeing your bag.

DIR ... at least my understanding of it ... involves considering the conditions you're likely diving in and applying common sense when determining what gear to take ... not following some "formula" that somebody who's probably never dived in your local conditions came up with. That's partly what they mean by "thinking diver" ...

... Bob (Grateful Diver)

 

[RJP]

DIR ... at least my understanding of it ... involves considering the conditions you're likely diving in and applying common sense when determining what gear to take ... not following some "formula" that somebody who's probably never dived in your local conditions came up with. That's partly what they mean by "thinking diver" ...

That sort of "thinking" will get you nowhere, Bob!

 

[MXGratefulDiver]

While you don't need a DIR boat, a complete stroke mess of a boat is a no-no for drift diving. In most cases the whole boat basically has to dive together and you use a float ball or shoot a bag for deco, depending on the conditions, type of dive, etc.

Irrespective of the boat, in my area that strategy won't work ... not even for DIR divers. Typical vis dictates teams of no more than three divers ... more than that raises the risk of losing visual contact too high ... even for highly trained DIR divers.

Around here we simply don't dive in groups. Four or more divers doing a drifting deco would sometimes require touch contact at 20 feet and above.

... Bob (Grateful Diver)

 

[Web Monkey]

Don't hire a boat guy unless he has really big ears.

Don't hire a boat guy unless he's a cyborg and the boat is completely unsinkable with a 100% failure-proof propulsion system.

Terry

 

[Clammy]

Pugetropolis....