Spring Heels for Apollo Fins

Chuck Tribolet
triblet@garlic.com
http://www.almaden.ibm.com/cs/people/triblet/

Spring heels for ScubaPro JetFins are commercially available from a number of sources, most notably Halcyon. And they are also available from Manta for most fins with lever action quick releases that attach to a mushroom-shaped knob on the side of the fin. And Apollo has a fits everything spring heel that requires drilling holes in the side of the foot pocket. I have a pair of Apollo fins (NOT BioFins) with a Fastex-style quick-release where you pinch the sides of the buckle to release it. I like them: they are a pretty blue, which looks looks nice in pictures my girlfriend Admiral Linda takes, and they motivate me pretty well. I get complaints from the JetFins folks that I go too fast. The Halcyon and <????> spring heels won't work, and the engineer in me is bothered by drilling holes in rubber. But I was breaking a couple of straps a year (I dive a LOT), and wanted the absolute reliability of stainless steel springs.

So I set about to create my own spring heels. I wanted to attach them via the normal buckles and have them pull in the same direction as the rubber straps, but there was no obvious way to attach the springs to the buckles. After about a year of cogitating about this over more than an few cold ones, I figured out that if I cut away part of the buckle, I could use a clevis pin with spacers to center the spring. Once I figured that out, my friend Scott Brown helped with the details of the rest.

Parts List:

Stainless Steel Springs: 11" OA with crossover loop ends, .500" OD, .0625" wire diameter, McMaster-Carr p/n 3932K54, $4.99 each, need 2 each.

Stainless Steel Clevis Pins: I cut down 3/32" by 3" clevis pins from OSH, but it looks like McMaster-Carr p/n 92390A110, $8.29 for a package of 10, would work as-is, need 4 each.

Nylon Unthreaded Round Spacers: 1/2" OD x .192" ID x 1/2" long, McMaster-Carr p/n 94639A554, $6.64 for a package of 100, need 9 each. You can get these in packages of one or two at major hardware stores.

#10 SS Washers: ??, need 13 each.

Stainless Steel Cotter Pins: 3/32" x 1/2" would be right, I cut down 3/32 x 1", West Marine sells a package of 8, need 4 each.

1" Tubular Nylon Webbing: need two pieces 12 inches long. I got it from REI.

Cave Line: Since I'm not a tech diver with reels of cave line laying about, I used 2 mm utility cord from REI, $.15 per foot, need 5 feet.

Here's one of the clips after I modified it, and one before. I removed the round cylinder that the old rubber strap made a 180 around, the two rectangular bits that sick out from the side, a little bit of the main structure so the nylon spaces would have a flat place to sit, and a bit of a ridge on the back of the flat button part.. I used a small milling machine, but it could all be done with hand tools. The cylinder just pops out.

I was fortunate to have a collection of clips from old broken straps.

Note the piece of "cave line" running down the middle of the spring. This is to keep you from over stretching the spring when you take the fins on and off. Make it long enough to get the fins on and off, but not much more. McMaster-Carr specs the springs to stretch 7.40", so 18.40" (= 11"OA + 7.40") should be the max length of the cave line.

Here's a picture showing how the cotter pin is installed. Note that the cotter pin sits down nice and flat on the washer under it. That's because I took an extra plastic spacer (that's why there are NINE in the parts list) and put it over the end of the clevis pin and squeezed it all in a vice.

Here's a picture showing an unmodified (therefore too long) clevis pin, spacers, washers, and unmodified (therefore too long) cotter pin. It shows the sequence of assembly. Modifying the clevis pins was a pain. I wish I'd checked McMaster-Carr first.

Here's a picture of the strap installed on the fin. Note that the fin is upside down in this picture. Also note that the cotter pin end of the buckle is down when the fin is on. This is because there's lots of space at that end.