Fin stabilsers at anchor - underwater video

[Lozzer]

hi JFM

\have you had any issues with collecting ground lines around the fins giving our style of mooring down here..

I recall your lazy line being tight when we used your berth last year.

Like the footage. Hope all is well.

L

 

[jfm]

Hey jfm, you must have got up very early to get a spot in Mondrago during August Excellent video of the stabs; surprised how fast acting they are

I got there the night before mike to get that spot. Arrived about 10pm direct from ibiza, and used 2 anchors. 25kg on the stern

The stabs were not moving fast in that vid. You ought to see them when they do move fast. I'll try to get another vid and post on here

 

[Deleted User YDKXO]

LOL, are you sure that diesel fumes don't remind you of your business, so you feel less guilty for taking some days off while you're boating?
Re. your question, well, if you wish to try also some "real" dives, I'm afraid that there's no substitute to the traditional diving gear.
Otoh, if you're just interested in scraping the boat now and then, you might consider either a small emergency cylinder, or a surface air supply which you could keep onboard, as the following ones:
Sea Breathe
Third Lung
A tad expensive, but they allow you to stay under the boat as long as you wish, with no equipment at all aside from the mouth piece and the connecting hose.
Of course, you could as well turn off your genset and continue to enjoy snorkeling...

With apologies to jfm for the o/t.

Thanks Mapism. A few years ago, I saw some self contained lightweight diving gear suitable only for shallow dives. It looked like a small backpack and you didn't need PADI training. I nearly bought it at the time but now for the life of me I can't remember the brand name. I think the cost at the time was about £600

 

[Deleted User YDKXO]

I got there the night before mike to get that spot. Arrived about 10pm direct from ibiza, and used 2 anchors. 25kg on the stern

The stabs were not moving fast in that vid. You ought to see them when they do move fast. I'll try to get another vid and post on here

I'm still quite surprised at the speed and range of movement of the fins even though you say they weren't operating at max. I had wondered how effective the fins would be at rest without water flowing over them but I can see now how aggressively they move. V impressive

 

[simon]

Mini B

Mike

I use this. Its OK for shallow dives and boat scrubbing.

Simon

http://www.mini-b.com/

 

[Deleted User YDKXO]

Mike

I use this. Its OK for shallow dives and boat scrubbing.

Simon

http://www.mini-b.com/

Thanks Simon. Thats the equipment I was thinking of. Is it any good?

 

[Nick_H]

The mini-b is only conventional SCUBA gear with smaller cylinders and nice packaging, so its not inherently any safer, and doesn't require any less training. It could be useful as a lightweight piece of kit for clearing ropes or netting from the stern gear, or checking hull/anodes etc, but I think it's quite limited in its use.

It takes me at least half an hour to scrub my stern gear, and its energetic work so I would use about half a full size tank of air. So, you need about 6 litres of cylinder capacity for that, which is 4 times more than the small mini-b set up. Mini-b do bigger tanks, but of course they get heavier, and the 10 litre mini b will be the same weight as a normal 10 litre SCUBA set up. Don't forget also that you need to have the cylinders filled at a dive shop, so the smaller the cylinder, the more often you need to get it filled. The min b set up with the tank slung horizontally across the lower back looks ergonomically wrong, as you want the weight up on your shoulders as much as possible.

 

[Deleted User YDKXO]

All good points, Nick_H. Their website refers to a 'Microdive' training course. Is this less onerous than a basic PADI course? Actually I'm not that interested in diving per se only in scraping the props occasionally or cutting away a prop foul so any diving gear on my boat would be usused for much of the time which is why the Mini B is of interest. Also, I guess it takes up less storage space than conventional dive equipment.
There is one other aspect to this. Having said that I'm not interested in diving myself, my SWMBO is interested. In fact, I bought her a beginner's PADI course a couple of years back but she suffers from asthma and was refused entry on to the course. Any idea whether the health requirements for the Microdive course are less onerous?

 

[EME]

All good points, Nick_H. Their website refers to a 'Microdive' training course. Is this less onerous than a basic PADI course? Actually I'm not that interested in diving per se only in scraping the props occasionally or cutting away a prop foul so any diving gear on my boat would be usused for much of the time which is why the Mini B is of interest. Also, I guess it takes up less storage space than conventional dive equipment.
There is one other aspect to this. Having said that I'm not interested in diving myself, my SWMBO is interested. In fact, I bought her a beginner's PADI course a couple of years back but she suffers from asthma and was refused entry on to the course. Any idea whether the health requirements for the Microdive course are less onerous?

Asthma is a no-no for PADI (or at least was). My son got around it by going to Thailand to learn without his father's knowledge I would add.

 

[vas]

... Don't forget also that you need to have the cylinders filled at a dive shop, so the smaller the cylinder, the more often you need to get it filled.

apologies for the continuation of the hijacking, but the site does mention a black air charging something whatnot. I thought they come with their own air compressor system to refil them, no?

 

[Nick_H]

All good points, Nick_H. Their website refers to a 'Microdive' training course. Is this less onerous than a basic PADI course? Actually I'm not that interested in diving per se only in scraping the props occasionally or cutting away a prop foul so any diving gear on my boat would be usused for much of the time which is why the Mini B is of interest. Also, I guess it takes up less storage space than conventional dive equipment.
There is one other aspect to this. Having said that I'm not interested in diving myself, my SWMBO is interested. In fact, I bought her a beginner's PADI course a couple of years back but she suffers from asthma and was refused entry on to the course. Any idea whether the health requirements for the Microdive course are less onerous?

The only way to reduce the level of training needed is to take more risks or limit the scope of the diving, and you can equally do this with the mini-b or conventional stuff, because its fundamentally the same. It's a bit like buying a dayboat so you don't need to learn about nav lights, fine as far as it goes but you could equally buy a 90' predator and not take it out at night. It's not the dayboat per se that reduces the need for training, it's the limitation you've accepted on how you use it

 

[Nick_H]

apologies for the continuation of the hijacking, but the site does mention a black air charging something whatnot. I thought they come with their own air compressor system to refil them, no?

The site says "The air cell provides buoyancy control on the surface and underwater" so I don't think its a compressor for the cylinders

 

[woodie1000]

Mike, I also suffer from asthma and looked into the diving thing a few years ago (maybe 7/8). At that time, you could do a PADI course with asthma but you had to have a chest x-ray done and then undergo a medical with a PADI approved doctor. I got the chest x-ray done but for one reason or another never got round to doing the medical. But just to let you know it is/was possible, if a bit of a pain.

 

[vas]

The site says "The air cell provides buoyancy control on the surface and underwater" so I don't think its a compressor for the cylinders

I'm talking about the supplied with tab on the site, third item down reads:
Black Air Cell with Power Inflator
not got a clue what that is

 

[Deleted User YDKXO]

The only way to reduce the level of training needed is to take more risks or limit the scope of the diving, and you can equally do this with the mini-b or conventional stuff, because its fundamentally the same. It's a bit like buying a dayboat so you don't need to learn about nav lights, fine as far as it goes but you could equally buy a 90' predator and not take it out at night. It's not the dayboat per se that reduces the need for training, it's the limitation you've accepted on how you use it

OK thanks

 

[Deleted User YDKXO]

Mike, I also suffer from asthma and looked into the diving thing a few years ago (maybe 7/8). At that time, you could do a PADI course with asthma but you had to have a chest x-ray done and then undergo a medical with a PADI approved doctor. I got the chest x-ray done but for one reason or another never got round to doing the medical. But just to let you know it is/was possible, if a bit of a pain.

Thanks. I'll look into it again for SWMBO. She has thing about swimming with the fishes and I know she'd love diving

 

[jonnybuoy]

Interesting vid jfm....how do they actually work? Are they sensing flow pressure and pushing back against it?

Jon.

 

[MapisM]

The fastest sweep eaves a "hole" in the water that you can see if you look down from the side deck, and then a big whirlpool as it fills. But people generally don't swim in those conditions so it's not a problem. I'll try to vid it next time I get the chance

J, did you have the opportunity to take any other clip in the meantime?
Your video made me thinking about the logic of fins at zero speed, because in principle I couldn't see a reason why also "normal" fins stabs shouldn't work at zero speed, at least to some extent.
Therefore, in the last week of cruising with some friends, I tried the behaviour of my stabs at anchor, and also took a brief video of them (at 3:00 of the video in this other thread).
Interestingly, they are somewhat effective also at zero speed, even if they were not designed for that. I suppose that the idea of stabilization at rest must have popped to the mind of someone who left traditional tabs switched on and noticed that they can do something also in total absence of water flow...
That said, they are now actually useless in practice, because the hydraulic pump is driven by one of the main engines, which must therefore be running.
Fitting a second AC pump driven by the genset could make sense also as a backup, though.
Mmm... food for (winter) thought!

 

[jfm]

J, did you have the opportunity to take any other clip in the meantime?
Your video made me thinking about the logic of fins at zero speed, because in principle I couldn't see a reason why also "normal" fins stabs shouldn't work at zero speed, at least to some extent.
Therefore, in the last week of cruising with some friends, I tried the behaviour of my stabs at anchor, and also took a brief video of them (at 3:00 of the video in this other thread).
Interestingly, they are somewhat effective also at zero speed, even if they were not designed for that. I suppose that the idea of stabilization at rest must have popped to the mind of someone who left traditional tabs switched on and noticed that they can do something also in total absence of water flow...
That said, they are now actually useless in practice, because the hydraulic pump is driven by one of the main engines, which must therefore be running.
Fitting a second AC pump driven by the genset could make sense also as a backup, though.
Mmm... food for (winter) thought!

I have not had the chance to get any more movies, sorry. In fact, since my last movie, there has been an incredible heatwave in the Med with virtually no wind or waves for well over a week

The main differences between fins at anchor and underway are (i) fin area (bigger is better, at anchor), (ii) hydraulic power (you need higher fin speed at anchor) and (iii) the algorithms (when in "at anchor" mode the systems switch to entirely different algorithms becuase the fins have to "swim" to stabilise the boat whereas underway they act as foils, and these are quite different things)

There is no problem with strength becuase the fin forces are higher underway than at anchor.

I can imagine your fins would help a bit at anchor but your algorithms/control electronics are still written on the assumption that the fins are foils not swimming fins, so the performance will suffer because of that. I wonder if swimming software could be retro fitted?

For zero speed power, you could fit a 230v motor and hydraulic pump but it's quite a big job. The 230v motor for your boat might need to be 5kw/7hp and then you are into 3-phase territory else your generator will not survive the start-up spikes. My motor is 8Kw/10hp approx, 3 phase. A better answer for you is maybe a direct PTO hydrualic pump on your genset. Also you need an accumulator to provide a second of instant hydrualic power when the valves open fast

 

[jfm]

Interesting vid jfm....how do they actually work? Are they sensing flow pressure and pushing back against it?

Jon.

Jon, they don't sense flow pressure. They mainly sense (i) accelerations (in many directions) using gyros, (ii) inclination using inclinometer (iii) speed using GPS and (iv) fin position using angle transducers on the fin shafts. A big motherboard then figures out, from all that data and using algrothms in the firmware, what movements to make the fins do