Jetfins Jets Jet Fin differences

[*Floater*]

I have recently acquired a whole set of used jets, plus a pair of (new) turtles for use with my drysuit. During this process I realized that there are many variations of this fin out there which is why you have to be extra careful when buying a pair - I hope this post will be of some help.

Lightning bolt: First note that there are jets with a lightning bolt across the SP logo, and then there are ones without the lightning bolt. My understanding is that the lightning bolt ones are made of a newer rubber compound still in use today whereas the other ones are some 20+ years old and use a thermo-plastic compound. My analysis is only for the lightning jets. I haven't tried the older ones.

Next you could look at kidspot's page for sizing: http://www.kidspot.org/personal/scuba/#fincomparison

His stats for the jet foot pockets are the following:

...........depth........width........height
M.........6.5"..........3.25"........2.75"
L..........7.5"..........3.5"..........2.75"
XL........8.5"..........3.75"........2.75"
Turtle...8.625".......4.375".......3.5"

The funny thing though is that my measurements came out different. Either we measure them differently, or his are of different model. For comparison, below are the measurements for my fins and some photos of how the measurements were taken (also see my gallery for width and height measurements):

...........depth........width*........height**
M.........7.5"..........3.5"............2.75"-3"
L..........8.25"........3.5-4".........2.85"-3"
XL........8.6"..........4-4.5".........3-3.25"
Turtle...8.75".........4.5-5.1"......3.2-3.5"

*the first measure is at the base, the second is around midway where the fin is widest
**the first measure is when fin is naturally shaped, the second is for when I pushed the bottom of the fin down to floor to straighten it out (some of them were curved).

As you can see there are some major differences between our measurements. For example, my mediums have the same stats as Tim's large jets. So be careful when you buy these. You might end up replacing your mediums that are too tight with large jets that are just as tight.

Lastly you should note that the lightning jets may have differnt markings. Mine all have the size written on the fin, plus the patent number at the back, whereas some of the ones on ebay do not. Also, next to size you sometimes have a number. My M's have no number, my L's have 4 and 6, respectively, and my XL's have flipped 2's on them. I have no clue what these mean, but when I bought the large ones to replace the mediums that were too tight, I made sure that the replacements were of the lightning model with the same patent number and size written on them, plus I asked the seller about the foot pocket sizing.

Below are some pics: M,L,XL and Turtle, respectively from left to right. The pairs displayed are M and L, L and XL, and XL and Turtle, respectively. The turtle is of course not a jet fin, but the generally prefered substitute for those who do not fit into an XL jet. There's also the XXL, but they are huge and only for those that do not fit into the turtles. I've also included a pic (from ebay) of a pair without the lightning bolt.

[kidspot]

I'm curious if we are measuring differently or if these are variations within the manufacturing process (which does vary some) All my measurements were internal (ie. not counting the thickness of the rubber) I measured the width of the foot pocket at the bottom of the footpocket opening. Height was measured in the middle of the footpocket opening. Depth of the foot pocket was highly subjective as I stopped measuring where the top of the foot pocket began it's descent (as far as a shoe would slide into it) this was hard on the mediums to judge because the foot pocket continued a long way inside still - measured inside the footpocket though, not the outside.

Let me know if we measured the same dimensions, because if so I would like to add your measurements to my site (if that's ok with you) to show the variation in the manufacturing process.

btw - I was quite surprised when I measured height of the footpocket that the M-XL were the same - I expected results more along the lines of what you got.

Aloha, Tim

[*Floater*]

For depth I pushed the ruler in as far as it would go. For height and width I took the inside emasurements at the mouth of the foot pocket as can be seen in the pics below (for size L).

I've often seen jetfins on ebay that don't have the size written on then and the seller has appeared unsure about it, so asking for measurements can helpful if you know what they should be. I used your site for that purpose.

[kidspot]

looks like we measure height and width the same, but differently on depth... Mind if I add your data to my charts?

Aloha, Tim

[*Floater*]

Originally Posted by kidspot

Let me know if we measured the same dimensions, because if so I would like to add your measurements to my site (if that's ok with you) to show the variation in the manufacturing process.

I think we measure the width and height more or less the same way, but the depth differently. I prefer to just take the max depth as it's objective and can be used to identify the size of a jetfin. You are welcome to add the measurements onto your site. Disregarding the depth, I think our other measurements are pretty close. There's always about 0.25" of difference in how one can measure. The XL jet has a taller foot pocket than M and L do though, it even looks like it does in your photos.

[kidspot]

Thanks - and I think I'll double check my measurements on the height

Aloha, Tim

[Walter]

Originally Posted by *Floater*

My understanding is that the lightning bolt ones are made of a newer rubber compound still in use today whereas the other ones are some 20+ years old and use a thermo-plastic compound.

Nope. They are both rubber, but the rubber composition differs. If they don't have the lightning bolt, they are more than 20 years old. I don't know exactly when the change was made, but I believe it was in the mid - late 70s.

[*Floater*]

Originally Posted by Walter

Nope. They are both rubber, but the rubber composition differs. If they don't have the lightning bolt, they are more than 20 years old. I don't know exactly when the change was made, but I believe it was in the mid - late 70s.

You are probably right. I got the thermo-plastics thing from a Divernet fin review article, but it's hardly an authoritative source: http://www.divernet.com/gear/fins999/fins999.htm