Positively buoyant Jet Fins?

[trpltongue]

Shotmaster, thanks for the detailed response and the idea of the vertical swim test! In fact, I don't own any fins just yet. My dive instructor has a bunch of gear and I've been trying different fins each time I go out. KenGordon, thanks for the recommendation and feedback on the F2's. I'll see what my instructor and the local shops have available to test out.

rongoodman, you are absolutely correct that I am brand new at this and I expect my posture will get much better with time. Having said that, my instructor is a friend and we've worked a lot on proper trim in my few dives so far. I am diving in only a skin suit, no WS, with 5mm boots. My buoyancy is good, once I get the BCD inflation set I only use my breathing to adjust my depth. Slightly arched back, arms comfortably in front of me, knees bent ~90 degress to get feet up, slight clench in the backside to stabilize my upper legs, minimum weight possible, positioned on upper tank band, tank fully forward so that my head just clears when looking forward. My trim stays level as long as I constantly flutter to keep some forward momentum. As soon as I stop, if I lock my body in position by flexing my abs/back/legs, I slowly rotate to vertical, head up. If I don't lock position, my legs/feet drop first, then my head rolls up. My wife and daughter who are also brand new simply float weightless in the water in a beautiful horizontal position with their feet 90 degrees above their knees, with no flutter kick required My daughter spent more than 2 minutes just looking at some fish in a bit of wreck without once kicking (yes I timed her as I was in awe). That's where I'd like to get to

 

[Macan]

I had a student over the weekend who's feet heavy. A simple reduction and redistribution of the correct amount of weights fixed It. She's now in good horizontal trim.

If you have a trim problem, look for a good Instructor who can diagnose the problem before buying new gear.

 

[KenGordon]

As per the post above, if you are new at this and are having a particular problem then get help from an instructor or experienced diver. Really there are very few new issues, if you have a problem then chances are someone has had it before. Trim takes time in the water mostly, eventually you will 'get it' and wonder how you ever had a problem. There will never be a day though when you try a new bit of gear and instantly go from useless to brilliant.

 

[trpltongue]

That's definitely good advice, and exactly what I'm doing. My dive instructor is actually a friend who's been diving for 15yrs, so he's spent a lot of extra time with me on my trim, reducing weight (currently using 12lb with a Mares BCD), using the shoulder pockets of the bcd to trim forward, etc. My avatar shows the last dive we did working on trim / buoyancy through the hoops.

So far, there are only 2 scenarios where I can keep my feet / legs up:
1) Move weight to the front shoulder pockets and extend my arms fully to tilt my body forward a bit and constantly flex my butt / hamstrings to keep feet up without kicking
2) Evenly distribute weight between shoulder pockets and integrated weight pockets to achieve neutral trim for my upper body, then constantly flutter to maintain some momentum

Interestingly, even in the weight forward position, holding weights in my fully outstretched hands (which causes my head to start to drop), if I relax my legs, my feet fall. I'm pretty sure it's just simple physics If your feet / legs are negatively buoyant, they will fall about the hinge point at your waist just like your arms. It's easy enough to lift your arms up, as they are light and you don't get tired. However, legs are heavy and it quickly becomes fatiguing to constantly flex to keep my feet up.

I'm going to keep working on it, going out again this weekend trying out a BP/W BCD and adjusting weighting some more, but I don't see any scenario where someone with negatively buoyant legs / feet can be neutral in the water without some sort of energy exertion (either flexing legs or constantly fluttering).

 

[halocline]

It is true that good trim is mostly about weight distribution. If you're using 12 lbs without a wetsuit (did I read that correctly) it sounds like you're overweighted. Probably the BC itself has some positive buoyancy and that, with an AL tank, can definitely screw with your trim. I would try putting some weight on the cambands.

Using fins that are slightly negative, neutral, or positive is, IMO, part of the weight distribution process, so don't be shy about trying different fins. I found switching to negative fins helped me stabilize in AL doubles. But with a single AL80, I trim out better in neutral fins.

 

[RainPilot]

Hey there. FWIW, there is a UTD dealer in Dubai, the neutral fins are about 600 AED and easy to get to Qatar. the UTD head for MENA comes to Qatar quite often, I'm sure a pair of fins can make it into the carry-on. PM me if you need any info.

On a different note, I am also a little foot heavy and i found that using thicker neoprene booties helped a lot. i normally dive 3mm short or just a skin but i always have my 7mm booties on, with the UTD neutral fins my feet stay where they need to without the back ache

 

[trpltongue]

RainPilot, that is excellent! I'm making a trip to the UAE in a little while. I may have to stop by. I was actually trying to get the 7mm boots but the dive shops here didn't have any.

halocline, I just checked my notes and I had 10 lbs. 2lbs in each ditchable weight pocket and 3 pounds in each of the shoulder pockets. I was trying to tip my balance away from my feet. I'm pretty sure it was a Mares or maybe Aqualung jacket style BCD and an AL80 tank. With this setup I was just barely negatively buoyant during my 3min safety stop with 50bar in the tank and my bcd as empty as I could make it. I'm 6'2" 175Lbs, average build up top but thick legs.

This weekend I'll be using a BP/W setup so I imagine I'll need a bit less weight, but I'm concerned about where to put it and still be able to ditch it. I don't want to have so much non removable weight up front that I'm negative with an empty wing

 

[kelemvor]

One way to test fin thrust is to swim vertical and see how high out of the water you can get your body. You will also feel where the stress points are in your body, ankles, knees, hips. This test destroys people's claims about fin performance. You can easily compare fins and have something as a standard to go by. It also gives a quick identification on comfort. I found the Novas to be a good compromise between all out performance and comfort. The vertical swim test is the best way to compare fins. After that some people may need something because they may use a particular finning technique like frog kicking for cave diving and choose something that works better for that application. I have tested some fins that I consider dangerous as you can't get enough thrust to swim against even mild currents. Hope you find this helpful.

That sounds kind of dangerous... air expansion injuries etc...

 

[trpltongue]

I assumed he meant from a 4-5 meters or less (i.e. snorkeling)

 

[Shotmaster]

That sounds kind of dangerous... air expansion injuries etc...

Hahaha, how about poolside or on the surface next to the boat? Only an idiot would pretend to be a dolphin with scuba and rapidly surface. The test uses body weight, you fin vertical and see how much thrust you can get, the more thrust, the higher you body rises above the water. I can get my upper body almost to the waistline out of the water with my jet fins. My Novas only get me up high enough that my chest is out of the water to about half way to my belly button. So my observation is that the Novas produce about 30-40% less thrust.