Fins! Negative bouyancy.

[Ellabee83]

Hi all,

I have had a quick look but can't see that it's been answered specifically.

So... I'm a big lass (more positive buoyancy!) and diving in the UK, so wearing a 7mm wetsuit (even more positive!). I'm having to compromise on weights (12kg) as if I go in fully weighted it's prohibitive in terms of wandering around with it on (a lot of long walks to get to shore/ pontoons) and also once I'm under 6m+, they become too heavy and I end up wallowing in the murk and needing loads of air to get me up at all.

We've found that lowering my tank helps, but I am rolling A LOT and then once we get that issue sorted, my legs float and I'm literally vertical.

Boat diving, I have to actively swim down, and once I'm down, I'm great and trim is really good. Shore diving, especially in our waves, I require an extra 5-6kg to get me weighted enough to stay stable. If I lose any of that, I am again, literally vertical and upside down.

I'm looking at some ankle weights to assist as my boots are 6mm Seac Pro hard sole boots- again, long walks- which is obviously going to affect trim. My current fins are tusa solla which are pretty light, I think 0.8kg each. So there's quite a lot of positive buoyancy at my feet vs a lot of weight around my core.

I'm also looking at getting some tech fins as they're denser and have negative buoyancy.

So far, I'm considering

Apeks rk3 hd
Scubapro supernova
4th element tech
Oms tribe

Does anyone have any particular comments on how these are for helping with negative buoyancy, and if so, any help on sizing?


As I mentioned, my boots are seac pro hard soles in a small (roughly 10cm x 25cm), I'm a 6-7 UK (39/40 EU) and according to the dimensions of the rk3hd info sheet, the size of my boots puts me into a super, which seems ridiculous.

Any input would be really appreciated.

Thanks!

B

 

[tbone1004]

I would get Scubapro Jet fins vs. any of those listed, maybe Hollis F1 but with any of those types of fins I hope your calves are in good shape because they are a bit of a butt kick.

Now, to address the real issue which is likely inappropriate gear configuration and real weighting issues.
Bioprene floats, but it does not need to be compensated for by the BC because it is considered static buoyancy, i.e. if it takes 10kg to sink you in a bathing suit at the surface you will still need that to stay down at 30m because adipose tissue is considered non-compressible at reasonable diving depths.

A 7mm suit should need no more than 10kg to get it to sink and that is not an unreasonable amount of buoyancy to compensate for with the BC and even with a large size tank a 30lb wing should be more than adequate. I was trying to figure out what you think you need in terms of lead and it sounds like 12+6kg=18kg total? That's ~40lbs which is a lot, but not unreasonable. What type of BC are you using? You would greatly benefit from a stainless steel backplate as it would not only help you shed some of the lead you are carrying on a belt *depending on the BC you are coming from you could easily shed 4kg for a negligible total rig weight increase*, and the one-piece harness will help with stability and security on your body far more than any standard BC would because it is custom fit to your curves and with the crotch strap it will actually stay where you put it. The single tank adapters will also help the tank be much more secure. That change alone will be a huge change of experience for you and likely be a game changer for your diving since you'll be able to actually dive adequately weighted and balanced.

Check out the recent blog post that @oya made about weight positioning which is a good read as well. Roger tends to be a bit passionate about the topics he blogs about so understand that going in, but the passion is there for a reason.

 

[Ellabee83]

I would get Scubapro Jet fins vs. any of those listed, maybe Hollis F1 but with any of those types of fins I hope your calves are in good shape because they are a bit of a butt kick.

Now, to address the real issue which is likely inappropriate gear configuration and real weighting issues.
Bioprene floats, but it does not need to be compensated for by the BC because it is considered static buoyancy, i.e. if it takes 10kg to sink you in a bathing suit at the surface you will still need that to stay down at 30m because adipose tissue is considered non-compressible at reasonable diving depths.

A 7mm suit should need no more than 10kg to get it to sink and that is not an unreasonable amount of buoyancy to compensate for with the BC and even with a large size tank a 30lb wing should be more than adequate. I was trying to figure out what you think you need in terms of lead and it sounds like 12+6kg=18kg total? That's ~40lbs which is a lot, but not unreasonable. What type of BC are you using? You would greatly benefit from a stainless steel backplate as it would not only help you shed some of the lead you are carrying on a belt *depending on the BC you are coming from you could easily shed 4kg for a negligible total rig weight increase*, and the one-piece harness will help with stability and security on your body far more than any standard BC would because it is custom fit to your curves and with the crotch strap it will actually stay where you put it. The single tank adapters will also help the tank be much more secure. That change alone will be a huge change of experience for you and likely be a game changer for your diving since you'll be able to actually dive adequately weighted and balanced.

Check out the recent blog post that @oya made about weight positioning which is a good read as well. Roger tends to be a bit passionate about the topics he blogs about so understand that going in, but the passion is there for a reason.

That's really helpful thanks.

So I use an AP Valves Buddy Profile BCD and I've got a 15l steel tank.

Weight wise, yes, about that. I think it's about 28lb on a boat dive, and I need the extra when I'm shore diving as the minute I am deep enough to actually swim, I start rolling around. With 28lb on a boat dive I'm able to control at the bottom really well. As soon as I get to about 6m on a shore dive, it's the same, but the swim out can be a bit of a pain, especially in any currents.

I'll check out the post, thank you. I'm not sure if I can swap the back plate in my BCD but I can have a look into it.

Thanks again,

B

 

[MaxBottomtime]

Jetfins, all the way.

 

[Marie13]

That's really helpful thanks.

So I use an AP Valves Buddy Profile BCD and I've got a 15l steel tank.

Weight wise, yes, about that. I think it's about 28lb on a boat dive, and I need the extra when I'm shore diving as the minute I am deep enough to actually swim, I start rolling around. With 28lb on a boat dive I'm able to control at the bottom really well. As soon as I get to about 6m on a shore dive, it's the same, but the swim out can be a bit of a pain, especially in any currents.

I'll check out the post, thank you. I'm not sure if I can swap the back plate in my BCD but I can have a look into it.

Thanks again,

B

You’re not likely to be able to add a steel backplate to your BC. You’d have to switch to a totally new setup, a backplate and wing.

Note on the ScubaPro jet fins. The sizing is really weird. Runs quite small.

 

[Ellabee83]

You’re likely to now be able to add a steel backplate to your BC. You’d have to switch to a totally new setup, a backplate and wing.

Note on the ScubaPro jet fins. The sizing is really weird. Runs quite small.

That's what I thought. I'm new and have just bought a BCD so don't really want to go and buy a new set up.

 

[Marie13]

That's what I thought. I'm new and have just bought a BCD so don't really want to go and buy a new set up.

See if you can borrow. Are you a member of a club?

 

[Pressurehead]

In the UK, give these guys a ring and talk to them: Best Fins for UK Diving | Mike's Dive Store

 

[Endler's]

... Shore diving, especially in our waves, I require an extra 5-6kg to get me weighted enough to stay stable. If I lose any of that, I am again, literally vertical and upside down.

Before ankle weights/heavier fins/etc...Try putting up to 6 kg ballast on rubber weight belt.

Rubber weight belts ride quite a bit lower on your hips, than webbing style.

Place weights on belt so that they lie against stomach/abdomen when buckled. Like this:

Photo from: Pullmyfinger

 

[Robert H. Diver]

X3 for the jet fins