Help me understand the effects of current on fins

[theduckguru]

Don't know much about how to kick with different fins, but if you got arthritis in your knees ScubaPros TwinJets seem to take a lot of the shock out so you can kick stronger.

 

[danvolker]

current has ZERO effect on the performance of a fin. If a fin can produce a relative velocity of 2 knots, then it can do 2 knots. Period end of story.

The ability of the diver to maintain a kick is also independent current. If the diver can only swim 2 knots then that's all they can do, if they can maintain it for 5 minutes or 60 minutes has nothing to do with current. Speed and endurance have lots to do with the FIN that an individual diver, so the DIVER has to find the fin that works best for them.



although I agree with most of what you said, these two points that you made are simply wrong. First- speed test of fins have conclusively shown that monofins, freediving fins, and a few Force Fins are all faster than the fastest splits. Second all splits on the markets are based on a common design, most people know this as the "Natures Wing" design, but what most people don't know is that the "Natures Wing" patent is in fact a direct rip off of the Foil Force Fin

Meesier,
I have been on several dives from charter boats, where the same divers are always showing up--and diving with us....Several of these divers use split fins. On most dives, they appear to be able to keep up fine as long as Sandra and I are in no hurry...However, whenever the current runs crosswise to the reef, instead of straight along the reef ( the normal north current pulling divers for miles over the reef) , the split fin divers have major trouble dealing with the cross current vector.
I do not know if there is some sort of disturbance in the splits when current is thrust past them at a side angle--maybe a vortex issue where the interactions of the two split fin pieces begin to interfere with each other...but I have had to intervene on several occaisions, and pull these divers back to the inshore ledge so they could stay on the dive with us.
Have you ever heard of anything like this ?

Regards,
Dan V

Note on Boynton dives**** typically gulf Stream created north current pulls divers directly over the reefs in Boynton. The reef system is relatively narrow, maybe 75 yards wide from the inshore ledge across the crown to the offshore facing fingers. The norm for north current is around 1 mph, but could get to 2.5 mph on some days. Put another way, on most days it is easiest to swim with the current, and it pushes you straight down the reef--but most divers could fight it and go up current for a few hundred yards if they needed to, on many of the dive days...BUT, there are days when very few divers could swim upcurrent, or even hold even against the current, if they are more than a foot or so off the bottom.
Then, on some days, instead of the current going straight down the reef, eddies from the gulf stream pull hard on the vectoring of the main current over the reef, and often this will pull divers to 45 degrees so that they will be pulled offshore and off of the reef into deep water, if they can not counter the side forces. Sometimes this could be tide related, sometimes it seems much too strong to be tidal.

 

[Teamcasa]

... Speed and endurance have lots to do with the FIN that an individual diver, so the DIVER has to find the fin that works best for them.

Speed is significantly more dependent on the divers technique and physicality than any fin.

Do you think that slipping on the best fin on the planet on a diver with little skill will instantly give them the ability to kick into a 1.5kt current better than a skilled diver wearing a set of mediocre quality fin? Hardly.

First- speed test of fins have conclusively shown that monofins, freediving fins, and a few Force Fins are all faster than the fastest splits.

Do you have any facts to back this up?

 

[meesier42]

Meesier,
I have been on several dives from charter boats, where the same divers are always showing up--and diving with us....Several of these divers use split fins. On most dives, they appear to be able to keep up fine as long as Sandra and I are in no hurry...However, whenever the current runs crosswise to the reef, instead of straight along the reef ( the normal north current pulling divers for miles over the reef) , the split fin divers have major trouble dealing with the cross current vector.
I do not know if there is some sort of disturbance in the splits when current is thrust past them at a side angle--maybe a vortex issue where the interactions of the two split fin pieces begin to interfere with each other...but I have had to intervene on several occaisions, and pull these divers back to the inshore ledge so they could stay on the dive with us.
Have you ever heard of anything like this ?

Regards,
Dan V

I have seen it and had to pull many people home after watching it. At the same time, I highly doubt the problem that those divers are experiencing has to do with their fins failing them, its their lack of skill. I would be willing to bet you could give those same divers a DPV and they would probably still not keep themselves where they belong.

As far as the mechanics of the splits failing in a side current due to their design, I can't say that I have observed any evidence to make me believe that this is true, but at the same time, I have no evidence to prove it false.

Speed is significantly more dependent on the divers technique and physicality than any fin.

Do you think that slipping on the best fin on the planet on a diver with little skill will instantly give them the ability to kick into a 1.5kt current better than a skilled diver wearing a set of mediocre quality fin? Hardly.

Do you have any facts to back this up?

maybe my point was less than clear, its the match of the fin characteristics and the divers technique and strength that produces speed and endurance. To that end I think we are in complete agreement.

 

[Walter]

----not with tag lines & doing a drift dive.....It's always straight ahead for me......

Many divers won't even be able to hold on in a 5 knot current, but some, and I'm sure you are one of them, will be able to pull themselves along a line against a 5 knot current. Of course, you can do that as easily without fins as with them (although fins do help keep you oriented). Ah, the drift dive, moving along with the current, easy in any fins and pretty easy without any fins at all.

Bottom line, both the situations you described have nothing to do with the question asked.

 

[diver 85]

Many divers won't even be able to hold on in a 5 knot current, but some, and I'm sure you are one of them, will be able to pull themselves along a line against a 5 knot current. Of course, you can do that as easily without fins as with them (although fins do help keep you oriented). Ah, the drift dive, moving along with the current, easy in any fins and pretty easy without any fins at all.

Bottom line, both the situations you described have nothing to do with the question asked.

sure it does---again I ask, you ever been in a current I described with SCUBA???-----trust me, you want to be wearing fins vs none---

 

[Puffer Fish]

Dan, I have seen that sort of issue, but it is not fin related, it is diver and location (where the diver finds themselves in relation to the current and the reef) I have a few hundred dives in that area (and can think of several other areas in the world with similar currents, and where you are and how well you use your fins can make a huge difference. When I think back about it, the worst I have ever seen was someone using tradition paddle fins.

For reasons I have never understood, there seems to be a terrible understanding of fins, even when there is a fair amount of test data and repeatable information out there.

A couple of the ones that get repeated over and over again are:

1. Split fins are a rip off of force fins. Well, for starters, both have US patents. So the patent office does not agree with that assesment.

Here is the original patent (1996 filing) High efficiency hydrofoil and swim fin designs (US5746631)

But to assert that a large highly flexable fin is somehow a copy of a short stiff, curved fin with a totally different foot attachment method is somehow a rip off of force fins is silly.

2. Force fins are faster and more efficient than split fins... based on a Navy evaluation. Sadly, that evaluation was done before split fins were on the market.... the Navy compared force fins to traditional paddle fins in that test. I have not been able to find anywhere force fins have been provided to make a direct comparison to splits...would be very interested if there was such data.

3. Free diving fins are faster... this one is half true. Long free diving fins can be faster, but they generate far less force... so a large diver, one with a tank on their back would be a serious disadvantage. The part that is true is that full foot fins are more efficient than open heel fins...but it has to do with the much smaller size around the foot area and how the foot attachment flexes. If a fin is available in a full foot version, it will almost always be more efficient.

There are other reasons to use fins besides just speed, efficiency and force that is generated. Included what you are used to, and the type of diving one is doing.

I happen to think that force fins (at least some of the many designs) have some merit, but over the years, the inventor has come up with as many silly designs as functional ones, and has rather over priced them.

The inventor of split fins (those using the patented Nature's Wing design), have used major company's to promote and sell the concept. I don't know the history, but given the timing and the location of both inventors, I have to believe that they may have worked together or at the very least, know each other. Of the two concepts, split fins have been a huge success, and Force fins survive..but I suspect this is more due to marketing than effective design.

Meesier,
I have been on several dives from charter boats, where the same divers are always showing up--and diving with us....Several of these divers use split fins. On most dives, they appear to be able to keep up fine as long as Sandra and I are in no hurry...However, whenever the current runs crosswise to the reef, instead of straight along the reef ( the normal north current pulling divers for miles over the reef) , the split fin divers have major trouble dealing with the cross current vector.
I do not know if there is some sort of disturbance in the splits when current is thrust past them at a side angle--maybe a vortex issue where the interactions of the two split fin pieces begin to interfere with each other...but I have had to intervene on several occaisions, and pull these divers back to the inshore ledge so they could stay on the dive with us.
Have you ever heard of anything like this ?

Regards,
Dan V



Note on Boynton dives**** typically gulf Stream created north current pulls divers directly over the reefs in Boynton. The reef system is relatively narrow, maybe 75 yards wide from the inshore ledge across the crown to the offshore facing fingers. The norm for north current is around 1 mph, but could get to 2.5 mph on some days. Put another way, on most days it is easiest to swim with the current, and it pushes you straight down the reef--but most divers could fight it and go up current for a few hundred yards if they needed to, on many of the dive days...BUT, there are days when very few divers could swim upcurrent, or even hold even against the current, if they are more than a foot or so off the bottom.
Then, on some days, instead of the current going straight down the reef, eddies from the gulf stream pull hard on the vectoring of the main current over the reef, and often this will pull divers to 45 degrees so that they will be pulled offshore and off of the reef into deep water, if they can not counter the side forces. Sometimes this could be tide related, sometimes it seems much too strong to be tidal.

 

[Coalcracker]

The long free diving fins seem to be best used by free divers so Mares and Cressi and other companies that have long made fins
also make fins for SCUBA diving with tanks, weights, dry and wetsuits etc.

 

[danvolker]

Dan, I have seen that sort of issue, but it is not fin related, it is diver and location (where the diver finds themselves in relation to the current and the reef) I have a few hundred dives in that area (and can think of several other areas in the world with similar currents, and where you are and how well you use your fins can make a huge difference. When I think back about it, the worst I have ever seen was someone using tradition paddle fins.

For reasons I have never understood, there seems to be a terrible understanding of fins, even when there is a fair amount of test data and repeatable information out there.

A couple of the ones that get repeated over and over again are:

1. Split fins are a rip off of force fins. Well, for starters, both have US patents. So the patent office does not agree with that assesment.

Here is the original patent (1996 filing) High efficiency hydrofoil and swim fin designs (US5746631)

But to assert that a large highly flexable fin is somehow a copy of a short stiff, curved fin with a totally different foot attachment method is somehow a rip off of force fins is silly.

2. Force fins are faster and more efficient than split fins... based on a Navy evaluation. Sadly, that evaluation was done before split fins were on the market.... the Navy compared force fins to traditional paddle fins in that test. I have not been able to find anywhere force fins have been provided to make a direct comparison to splits...would be very interested if there was such data.

3. Free diving fins are faster... this one is half true. Long free diving fins can be faster, but they generate far less force... so a large diver, one with a tank on their back would be a serious disadvantage. The part that is true is that full foot fins are more efficient than open heel fins...but it has to do with the much smaller size around the foot area and how the foot attachment flexes. If a fin is available in a full foot version, it will almost always be more efficient.

There are other reasons to use fins besides just speed, efficiency and force that is generated. Included what you are used to, and the type of diving one is doing.

I happen to think that force fins (at least some of the many designs) have some merit, but over the years, the inventor has come up with as many silly designs as functional ones, and has rather over priced them.

The inventor of split fins (those using the patented Nature's Wing design), have used major company's to promote and sell the concept. I don't know the history, but given the timing and the location of both inventors, I have to believe that they may have worked together or at the very least, know each other. Of the two concepts, split fins have been a huge success, and Force fins survive..but I suspect this is more due to marketing than effective design.

Captain Happy,
Great post....let me adress these individually
1.) the Split fin "rip off" issue....I got this sentiment from many arguements I had with many of the most ardent Force fin supporters over the last dozen years or so....I would guess one of them that is on this sub forum could step in with the actual complaint that they have--what I would say is only that a patent is kind of ridiculous to protect you if you are a small volume entrepreneur, and the "infringer" is a large corporation. Your cost to defend the patent each year could quickly bankrupt you, and if you do not defend it, it is "history". In the USA, the odds are typically stacked in favor of the large corporation.
2.) I would love to create an Underwater race in South Florida...Upcurrent for a mile or so on a 60 foot deep Boynton Reef would be ideal. Each contestent would have a safety diver/referee along side them throughout the dive, using a Gavin Scooter ---when any contestant gets down to 1000 psi, the race is over, and the referee marks the location with a float hooked to the bottom ( later this is gps marked and speed & distance calculated). This could probably be done in heats of 4 to 6 divers at a time ( I know I could come up with that many scooter divers).
My bet is that a freedive fin wearing scuba diver will win this
3.)The freedive fin differences between brands are huge, and the differences between models made even by one mfg can be huge. Typically, very good freedive fin companies make fins aimed at the purpose of the fin....all day spearfishing competition fins are very soft, and good for finning for up to 8 hour days--they will not go as fast for a 5 minute effort, or one minute effort, but for "some people", they "may" match cardio/neuro/muscle issues of scuba efficiency better than the several stiffer versions aimed at shorter/deeper uses. Some fins are named by the depth range they are designed for, also suggesting time--if you use a 40 meter fin ( for doing 40 meter drops), you are going to trash your legs/exhause yourself in an hour or so, meaning this is close to the opposite of the all day kind of freediving fin.
For me, the 40 meter C4's are ideal for scuba diving..this carbon fiber fin has a huge return of power from each kick, it is easy for me to maintain a "bend" in each fin for a maximum amount of time in a large amplitude kick stroke( meaning easy thrust for longer)....the fin is more optimal for me because I am a competitive cyclist, and my leg stregth and cardio are not related to typical scuba divers.
The C4's also have taken the footbed power transfer issue another stap forward--the foot pockets are individual--there is a left fina and a right fin pocket, and they fit like very good running shoes. They cost as much as some scooters, but they do not need charging, and don't weigh anything ( relatively speaking


Regards,
Dan V

 

[Bob Evans]

Dan, The subject of Split fin's reminds me how the whole rip off put my wife Susanne in Cottage Hospital, Santa Barbara. She was more important to me than being tied up with the land sharks. She is the one who can tell the whole story. Maybe, I can ask her again to set the records straight, it's truly a Amazing story.