If you think that strength is the main factor to consider in snorkel keepers, you are dangerously mistaken.
The single most important feature in a snorkel keeper is its drag resistance. I will address the kevlar keeper below, but in order to properly discuss the drag issue, it is important to isolate the variables involved.
Drag equals Dynamic Pressure * Surface Area * Coefficient of Drag or:
D=1/2 pV^2 * S * CvD
where
p = density of water (I used freshwater in my calculations to be conservative)
V = Velocity (the "safe" ascent rate of 30'/min)
S = Surface Area (the two keepers I've compared are nominally different)
CvD = Coefficient of Drag (in this instance, it's related to the model and material - both test keepers were silicone which has a significantly lower coefficient of drag than kevlar)
Using the two snorkel keepers shown below (again, both are silicone), one can see that their main difference is shape.
Test Subject 1
http://www.momentoffame.com/snapshots/MomentOfFame/l19692.jpg
Test Subject 2
http://www.momentoffame.com/snapshots/MomentOfFame/l19689.jpg
Although one might think that the larger size of Test Subject 2 would be a detriment, considering the increased surface area, When the model is folded in half (as it would be worn) and run through a water tunnel simulator, you can clearly see that the trailing protrusion actually reduces drag when compared to Test Subject 1 (see figures 3 and 4).
http://www.momentoffame.com/snapshots/MomentOfFame/l19690.jpg
figure 3
http://www.momentoffame.com/snapshots/MomentOfFame/l19690.jpg
figure 4
So looking at the facts shown above, one can clearly see that if you choose you use a snorkel keeper like Test Subject 2, you could probably get by with a 13CF pony. However, if you suffer from the increased drag of a keeper like Test Subject 1, you had better go with at least a 19CF pony. And Kevlar Keepers? If you foolishly decide to use one of them for their "strength," you had better just go ahead and strap on another 80
Final Design:
Designed using Pro/Engineer 2001 solid modeling tool, this snorkel keeper is assumed to be made out of medical grade silicone rubber impregnated with Teflon and dipped in a light silicone-based oil (can't tell you details, looking for a patent), see link below. We ultimately selected Test subject Design 1, because those extra tabs cost us 1/10 of a penny on a lot of 100, which means a $22.50 hit in a 1 year production run.
http://www.momentoffame.com/snapshots/MomentOfFame/l19696.jpg
The single most important feature in a snorkel keeper is its drag resistance. I will address the kevlar keeper below, but in order to properly discuss the drag issue, it is important to isolate the variables involved.
Drag equals Dynamic Pressure * Surface Area * Coefficient of Drag or:
D=1/2 pV^2 * S * CvD
where
p = density of water (I used freshwater in my calculations to be conservative)
V = Velocity (the "safe" ascent rate of 30'/min)
S = Surface Area (the two keepers I've compared are nominally different)
CvD = Coefficient of Drag (in this instance, it's related to the model and material - both test keepers were silicone which has a significantly lower coefficient of drag than kevlar)
Using the two snorkel keepers shown below (again, both are silicone), one can see that their main difference is shape.
Test Subject 1
http://www.momentoffame.com/snapshots/MomentOfFame/l19692.jpg
Test Subject 2
http://www.momentoffame.com/snapshots/MomentOfFame/l19689.jpg
Although one might think that the larger size of Test Subject 2 would be a detriment, considering the increased surface area, When the model is folded in half (as it would be worn) and run through a water tunnel simulator, you can clearly see that the trailing protrusion actually reduces drag when compared to Test Subject 1 (see figures 3 and 4).
http://www.momentoffame.com/snapshots/MomentOfFame/l19690.jpg
figure 3
http://www.momentoffame.com/snapshots/MomentOfFame/l19690.jpg
figure 4
So looking at the facts shown above, one can clearly see that if you choose you use a snorkel keeper like Test Subject 2, you could probably get by with a 13CF pony. However, if you suffer from the increased drag of a keeper like Test Subject 1, you had better go with at least a 19CF pony. And Kevlar Keepers? If you foolishly decide to use one of them for their "strength," you had better just go ahead and strap on another 80
Final Design:
Designed using Pro/Engineer 2001 solid modeling tool, this snorkel keeper is assumed to be made out of medical grade silicone rubber impregnated with Teflon and dipped in a light silicone-based oil (can't tell you details, looking for a patent), see link below. We ultimately selected Test subject Design 1, because those extra tabs cost us 1/10 of a penny on a lot of 100, which means a $22.50 hit in a 1 year production run.
http://www.momentoffame.com/snapshots/MomentOfFame/l19696.jpg
