Split Fin Physics

[Blackwood]

Today, I was in the pool again, but not to get any numbers. I have bought a pair of used Force Fins, and wanted to try them beside my scoop fins. They will take some time to get used to for me, as they have a very different kick.

Yah. I met up with Bob Evans (of Force Fins) yesterday and he showed me some of his fins and we talked a little about what kick styles each type is meant for. The original force fin works best with a very shallow (i.e. low amplitude) kick, whereas I'd imagine your scoop wouldn't be doing much in that middle range of motion. It will be hard to compare them ceteris paribus.

He also handed me a couple pairs of his own personal fins to try, Military SD1s and one that I'm not sure it on the market yet but he thinks works well with frog kicks (which I do most of the time).

I'm on my way to do some two bottle diving, and I'm bring them along. I think I'll hold off until I have a feel for the current, though, as they have much less area than my standard fins (XL Jets).

 

[Lepomis]

Hi John/SeaRat,

Thanks for your comments and info.

I agree that things often seem to get lost in (or even before) the manufacturing. In fact, one of the things that I have often wondered about in my years of fin testing and encountering some really poorly performing fins is whether some manufacturers even test their fins under diving conditions before releasing them to the market?! I won't name any fin names, but, for example, one kind that we tested one year with ScubaLab was so bad that after we (the test team members) would run a test with it, we actually stopped kicking with the fins and simply used our arms to get outselves back to the base point for the next set of fins and test run! And many fins that I've tried seem to have been designed more for looks and fashion than function.

DSAO -- and take gear advertising with a grain of salt
Jim

PS I love your "SeaRat" name! When I was a kid growing up, I spent a lot of time on the Mississippi River with an old man and his boat. We called ourselves river rats who belonged to the "Royal Order of River Rats" ... of which we were our own little club with only the two of us in it.

 

[Bob Evans]

SeaRat, if you were really serious about testing fins, why did you not call me on my toll free number? We could go over the different fins and their applications? What model Force fin did you buy? If they hurt your foot, are they too small? What size are they and from which lot and year? I wear a pair that fins barefoot for an hour swimming everyday.

 

[David Wilson]

I love your "SeaRat" name! When I was a kid growing up, I spent a lot of time on the Mississippi River with an old man and his boat. We called ourselves river rats who belonged to the "Royal Order of River Rats" ... of which we were our own little club with only the two of us in it.

Interesting that you in the USA called yourselves the Royal Order of River Rats, while we here in the United Kingdom have our Grand Order of Water Rats, a reversal of the traditional use of these adjectives in our respective countries. The Grand Order of Water Rats, based in London, has nothing to do with water or rodents: it's an entertainment industry charity.

Grand Order of Water Rats - Wikipedia, the free encyclopedia

I love the Mississippi as it flows through the Twin Cities in Minnesota. I've also been up to the river's source. I see you're from Fargo-Moorhead territory. My brother, who lives as a naturalised American citizen in Minneapolis, drove me up seven or eight years ago to North Dakota, taking in Fargo on the way. We ended up in Aneta, ND, visiting friends. Aneta is such a lovely timeless place, reminding me of one of those old-fashioned prairie towns in Hollywood westerns with its general goods store and thoughtfully positioned benches. All that was missing was a James Stewart character in a long apron, sweeping up outside the store!

Apologies to the rest of you for interrupting the thread with a few reminiscences on my part.

 

[Blackwood]

Interesting that you in the USA called yourselves the Royal Order of River Rats, while we here in the United Kingdom have our Grand Order of Water Rats, a reversal of the traditional use of these adjectives in our respective countries.

All americans appreciate alliteration.

 

[David Wilson]

All americans appreciate alliteration.

Vocalic as well as consonantal by the sound of it.

 

[John C. Ratliff]

SeaRat, if you were really serious about testing fins, why did you not call me on my toll free number? We could go over the different fins and their applications? What model Force fin did you buy? If they hurt your foot, are they too small? What size are they and from which lot and year? I wear a pair that fins barefoot for an hour swimming everyday.

Bob,

The Force Fins I bought were at a LDS, and had been there for some time. I picked them up for a good price. They are Large, but probably quite old as the only other designation they have on them is "L Pat.Pend." They are a Large size, but have no other markings other than the Force Fin logo on the top of the footpocket. There is no lot number or year markings.

Concerning the Force Fins hurting my foot, it is probably because I was using only a sock on my foot, and they came up onto my tarsal joint. They should be much better with some neoprene booties.

I did not call you because I don't have your toll free number, and haven't contacted any manufacturers yet. I may take you up on this offer though.

Bob, I will be putting those fins back in the water this coming week, and become more familiar with them. I am already finding that I need a wider dolphin kick with them, as the fins are somewhat wider and when used with a narrow kick they seem to interfere with each other. I will be using a neoprene bootie with them, which should take care of the problem I was having with their fit.

SeaRat

 

[John C. Ratliff]

Hi John/SeaRat,

Thanks for your comments and info...

DSAO -- and take gear advertising with a grain of salt
Jim

PS I love your "SeaRat" name! When I was a kid growing up, I spent a lot of time on the Mississippi River with an old man and his boat. We called ourselves river rats who belonged to the "Royal Order of River Rats" ... of which we were our own little club with only the two of us in it.

Jim,

Thanks for that comment; not too many people know where I got that nickname, but it dates way back. In 1971 I was a smokejumper in Alaska (came up from North Cascade Smokejumper Base in Winthrop, Washington), and had just come off a long fire. We had eaten C-Rations for a week, and we had a steak dinner. Well, I was still hungry after the steak ran out, and so ate another C-Ration. From that, I got the nickname "C-Rat." Well, I also was in the USAF Reserves at the time, and they had been calling me "SEA-Rat" because I had served in Vietnam (Southeast Asia); it stood for "Southeast Asia Ratliff," as someone thought there was another Ratliff in Europe (never confirmed though). So it became "SEA-Rat." When I started writing on this and other boards, I brought it back as it had a history with me, and sounded right for me. I simply changed it to "SeaRat" for convenience and because I love the sea.

SeaRat (John)

 

[Puffer Fish]

Lepomis,

I'm really glad you are here. There is a lot to talk about when it comes to fin hydrodynamics, and you can provide us with some good information. I've been looking at fin design for thirty years, and your ideas about water flow are along the same lines (like my string experiments in the 1970s) as mine.

Today, I was in the pool again, but not to get any numbers. I have bought a pair of used Force Fins, and wanted to try them beside my scoop fins. They will take some time to get used to for me, as they have a very different kick. I do know that their foot pocket is very uncomfortable with only a sock on, so I may try a neoprene bootie noxt time.

I also could not very well compare the Force Fins against my scoop fin, as I brought one scoop and one split fin to the pool. I found that they work well together though.

Also, I bought a pair of Farallon fins with the lower leg support off E-Bay for a nominal amount. I had a pair when they first came out, but they were really bad because the support would not allow the fin to be oriented correctly to push against the water. This is another case of a fin whose engineering principal was great, but the advantage was lost in the manufacture of the fin--lack of attention to details. It has another problem in that the rubber was of two different compounds, and over time the one has separated from the other, resulting in a broken rib on both fins. I plan to try adjusting the support to allow the extension needed for the blade, grind off the current blade and attach another of my choosing. It should be an interesting project, as one major limitation to pushing the fin is the strength of the ankle.

Anyway, I am happy to see you here, and we can have some more discussions.

SeaRat

Farrallon fins.. wow, have not heard anyone mention them in a very, very long time... had a pair... is an example that... well missed the mark ( I had a pair for a while....just could not take the pain). Wonder if they could be made to work with different materials and angles...

 

[mdb]

PF: I was working at Farallon at the time. We were testing the fins @ the old Ed Brawely's store in the pool. The fin would "lock Up" your ankle but was not very efficient for any kick styles. It was a stiff rubber fin, very uncomfortable and not at all efficient. The fins looked "cool" but they did not work. Anyone who has a pair has a relic.