Modifying fins, cutting, trimming etc.

[SangP]

Thanks Bob and David,

I guess I won't notch the fins after all. However, John C. Ratliff aka SeaRat's description of a homemade split and scoop fin mod does sound interesting.

Will go bug him to see if the idea on the mares has any merit.

Cheers,

SangP

 

[John C. Ratliff]

Hi SangP,

I got your PM, and will make some comments here. I will also answer some of Bob's input too.

I see you found my photos that I took in Alexander Springs State Park in 1970. If you want to see more on the scoop fin, look on this Vintage Scuba Supply website.

Your problem with the Mares Quattro, and I'm assuming that this is the Quattro Excel, has to do with the fin design for the upstroke. Bob has for years been talking about the problems of flat blades and their resistance on the upstroke, which is the basis for his original Force Fins (no resistance on the upstroke). It is this resistance which is causing you the cramps and pain. I was disappointed that Mares did not go to a full-out scoop fin design when they designed the Quattro Excel. They got the idea right (sort of) on the down stroke, where there is a pretty good scooping action of the blade. But due to the side walls of the fin just beyond the foot pocket, there is no bending of the fin blade on the up stroke until about half way down the blade. This presents a huge surface area (more than 6" x 9", or 54 square inches) that you have to drag through the water to "recover."

So, how to modify the Mares Quattro Excel to make them better? I have a pair, and have tried them against my home-made scoop fin design based upon the earlier Mares Plana design, which I modified with a scoop. The earlier design allowed bending just below the foot pocket, but the Quattros don't. So my initial modification would be to cut out just about all of the black rubber part of that rib down to the plastic to allow bending at the foot pocket. I'd retain about a quarter inch of material, and try it. If it still doesn't bend there, then I would cut it down further. Since I have a pair, if you'd like I'll do that to mine and report back. The blade itself does cup to form the scoop, but not as much as I like. Mine form a 180 degree circle at the end of the fin. The Mares Quattro are close to the 180 degrees on the downstroke, but only slightly cupped on the upstroke due to the problems with the design of the ribs not allowing the bending action necessary.

Now, on the thoughts that Bob Evans stated, that the strings from the scoop fin come out at a 90 degree angle to the direction of travel, I'd like him to look again. The strings actually move out at the plane of the flexible scoop membrane until they hit still water several inches away.

Here is the patent that covered the scoop fin design:

I'll have more informaton later--supper time (I'm being called;-)

SeaRat

 

[SangP]

Many thanks John,

However, the fins are just regular quattros not the excel version.

The thing about those fins are quite similar as you described. For some reason, I find the quattros harder on my calves than my L jets on both the up and down stroke. Guess that why they made the super channel.

Have a good dinner, I'll be patiently waiting for more info like making the quattros into a split, pivot or scoop or whatever.

SangP

 

[John C. Ratliff]

SangP,

My mistake on the type of fins; in your case, I would simply do the complete scoop fin modification that I did on the Mares Plana. You will need some flexible material (it can be rubberized nylon, or a PVC material), and cut out a piece that fits the cut you make in the fin blade itself. The material should be the same dimensions as the area you want to fill at the toe, and then have enough material at the fin tip to form a 180 degree semi-circle. I used the material from the fin blade cut into strips to make the pieces to sandwich the flexible scoop, and used both glue and pop rivets to secure the pieces. Here are the photos:

This shows the area I cut out, starting about 2.5 cm below the toe. I left about a 2 cm side area to rivet against. What I would do is to follow the black rubber, and cut out everything in between. I would then use the inside pieces for the sandwich. Here's the back photo:

This shows how the sandwich would work to retain the flexible membrane.

By the way, this is what they look like compared to the Scubapro Lightning Jet Fin (which I still have and use from about 1973); the Lightning Jet Fin is a great fin, but not better than the scoop fin modification.

I used my scoop fins yesterday during three dives in the Clackamas River, and they worked very nicely indeed!

I have also placed photos of the cut below, so that if per chance you cannot see the PhotoBucket photos, you can see these.

Good luck,

SeaRat

 

[John C. Ratliff]

Bob,

It sounds like you have been traveling, as have I. I have presented at two international conferences in the last month and a half, on safety topics unrelated to diving. This is why I have not been in touch with you--it's been a very busy and challenging spring.

While I am interested in fin design and do want to talk to you about that, I have some other concepts I have been working on for underwater swimming that I'd also like to discuss. I'm getting to the age where it is not so important that I profit from these concepts, but that they get out there so that they can be used.

SeaRat

 

[Bob Evans]

John, look forward to your call. Took a nice walk around our White House out to the Washington Monument early this Monday morning. It is hot, hot here in Washington D.C.. Enjoy looking at your scoop changes. I will post some cool photo's of my Fab Force experimental scooped blades once I get home. I was not impressed with the performance over some other changes that I could make almost overnight with Sewing urethane sheet together and pumping cast urethane into finger like channels. This non-molding patent allowed me to make so many fin designs each doing something different. I plan to retire soon from fins into the wave and wind energy business, so lets talk sooner than later. Best, Bob

 

[SangP]

Hi Bob,

I have a question regarding the design of the force fins. Now I know that the fins work under the rebound principle and are easier on the up stroke while power is generated on the down stroke.

This also lend it to work better with tighter and faster kicks. However, this strength doesn't seem to work as well for frog kicks and backward fining at least for me.

Would making a fin with a double scoop on the top and bottom give it more flexibility for a wider variety of fining techniques.

This is merely a question from a bad ff user

SangP

 

[Bob Evans]

SangP, that's a hard question for me. I was never really good at baseball. Hitting the ball never was my bag..did that mean something was wrong with the Bat?. Over the past 30 years I have seen divers who hit home runs with my fins and others who walk....

 

[SangP]

LOL! I did say I was a bad ff user didn't I.

SangP

 

[John C. Ratliff]

SangP,

There are two ways to do the frog kick. Some of us who grew up on swim teams do the frog kick with the bottom of our feet, and this would not work well with the Force Fins. But I've seen some divers in U/W videos do the frog kick with the top of their feet; this would work much better with the Force Fins.

SeaRat