Stabilizers for Blue Angel, engineering question

[jfm]

I,d have thought it pretty obvious if your fin can move/ respond faster ,then it can be smaller to achieve same effect all else being equal

No it doesn't achieve the same effect. Sure it has the same effect while it's doing its thing, but but if it moves faster it moves for less time. (Because, all fin stabs at anchor have a stroke limitation of about +/-45 degrees). This is the whole point: a smaller+faster fin is more susceptible to running out of effect before the wave has finished than a slower moving fin, and therefore it doesn't achieve the same effect so far as stabilisation of the boat is concerned, AOTBE, except in small waves of course.

 

[Portofino]

"susceptible to running out of effect before the wave has finished than a slower moving fin, "quote JFM

Agree ,but does it actually run out of effect ? What happens if it does not run out , how do you know ,how do they know?---
I would have thought, they would have done tank tests/ mock ups etc before arriving at the explanation re to justify smaller fin size for a given boat.
As MapishM says they have a wide range of fin size,s as you can see., which are presumably matched ( sorry) to the boat
Power steering in cars has/ is moving from hydraulic to electic for inc response ( and lower improved CO2 - by binning the PS belt driven pump) .
We need somebody with a boat a decent size to come along and say, " I have speced those" ------ and ----
1 - they are great, - work a treat, - fin size what are you one about, don,t bore me with this technobabble .Or
2- they are rubish, waste of money, only work in really small waves useless if it's choppy, ah I see what you mean, it's because the fins are a bit small - thought so cos snorkelling round my mate ,s boat same size his are hydraulic and work a treat
Or
Thing is they work, and that post kinda, explains how/ why + host of other benefits ,I think the physics is credible ,
Really need to go behind the R+ D ,I do not think its a black art, easy to test out

 

[petem]

Maybe the small fins do a little bit of paddling at the top of the stroke!

 

[Erik C]

So here we have a bunch of experienced knowledgeable boat owners not being able to agree on questions like fin size, heat dissipation, effectiveness, proven vs marketing BS, etc etc. Not a good sign if you ask me.

 

[Portofino]

Simple terms
Two identical boats@ anchor - one with hydraulic- t,other with these electic stabs -Same fin area
Wave come in beam on.
Both start to roll , this the important bit @ 1 cm off the flat centre the electic system has detected and reacted and " expressed " enough energy to damp through it fins- boat flattens
Meanwhile by the time the slower reacting hydraulic boat detects / reacts it would be 1 1/2 or even 2 cm off plane if it had the same size fins .peeps on board would not notice ,but requires grater forces now cos it been "slow out f the blocks "
But in reality to achieve the same damping ,once up as running it needs bigger fins which is what you have.
Ultimately in big sea @ anchor as the waves got bigger / more frequent etc then the big fin will finally be the better option last boat standing - , but by that time even with stabs ,both will be "running out of effect before the wave has finished" as JFM says ,

 

[BartW]

Simple terms
Two identical boats@ anchor - one with hydraulic- t,other with these electic stabs -Same fin area
Wave come in beam on.
Both start to roll , this the important bit @ 1 cm off the flat centre the electic system has detected and reacted and " expressed " enough energy to damp through it fins- boat flattens
Meanwhile by the time the slower reacting hydraulic boat detects / reacts it would be 1 1/2 or even 2 cm off plane .....,

agree,
this is exactly how I understood from CMC, how they explain that there is a advantage of the electric system compared to the hydraulic

 

[jfm]

the important bit @ 1 cm off the flat centre the electic system has detected and reacted and " expressed " enough energy to damp through it fins- boat flattens
Meanwhile by the time the slower reacting hydraulic boat detects / reacts it would be 1 1/2 or even 2 cm off plane

To move the electrics you have to spin up a motor and gearbox from rest, or oftentimes 2x that because you are slow it down from going one direction and spinning it up in the other direction. To move the hydruaulics you move a tiny-weight solenoid valve about 30mm and bang, they're out of the blocks. The hydraulic pump was already running and has forgotten what blocks look like, and the pressure reservoir was already charged up. Think about the vibrating feel on your brake pedal with ABS - that is a hydruaulic valve opening and shutting, and your brake calipers opening/closing, multiple times a second. Do you think that could be done better with an electric motor and gearbox moving the calipers in/out?

So why do you say electric is faster? Do you believe something just becuase a company writes it on a website?

 

[BartW]

there is no reason why a hydraulic system is inherently slower than electrical, in fact there are many reasons why hydraulics should be more responsive than an electric system, all to do with stored energy, ram and piston design etc. An electric system will need some sort of gearbox, which will increase inertia, above that of a well designed hydraulic system. An electric system could benefit from a really good sensing and control protocol, but so can a hydraulic device.

I disagree with this Rafiki,
the hydraulic systems I've seen in boats are simple valve controlled systems,
which can just be switched on and off (AFAIK)

a typical feature of a brusless DC motor (as used in this stab system) is that the electric current is controlled by a processer, which has very accurate controll over speed, power, acceleration,.... as you might have seen using in Robots.
No high precision robot is driven by hydraulics now aday's, but mostly by processor controlled electric DC motors, (AFAIK)
moreover there is a very accurate gear in there, with a huge reduction ratio, = very large lever arm.

 

[jfm]

I disagree with this Rafiki,
the hydraulic systems I've seen in boats are simple valve controlled systems,
which can just be switched on and off (AFAIK)

a typical feature of a brusless DC motor (as used in this stab system) is that the electric current is controlled by a processer, which has very accurate controll over speed, power, acceleration,.... as you might have seen using in Robots.
No high precision robot is driven by hydraulics now aday's, but mostly by processor controlled electric DC motors, (AFAIK)
moreover there is a very accurate gear in there, with a huge reduction ratio, = very large lever arm.

DC motors are perfect for robots becuase they can position the robot's tool with wonderful accuracy. There is no way you can position a hydraulic robot's tool with the same accuracy as a DC motor robot's tool. However, when looking for a prime mover in a robot, the ability to accelerate and decelerate the tool is somewhat further down the priority list.

 

[BartW]

hi Bart,

My first post, I have read the thread on rebuild and fins installation (almost) from the start.

I have been selling smaller US built console boats in France and Italy (Boston Whaler at the start, Sailfish now) since almost 10 years. When in serious trouble, I have had great help from a surveyor in Toulon... I dont know if your analysis and naval architects questions are still open, if so, please check him out, it's an official approved french surveyor of dutch origin who lives in Toulon (jan.verbeek@wanadoo.fr). Might be helpful.

If you want feedback on the Wesmar system, please try Pierre Marechal at Arie De Boom service yard in la Napoule (pierre@ariedeboom.com). French name, but belgian origin, speaks dutch. I know Wesmar is a hydraulic system, it might be too large/complicated. They have done retrofits on numerous vessels and are a great team to work with.

Good luck,

Mark

thanks Mark for the pointers, not needed right now, but will keep this in mind in case that ...
Looking at your forum name, I guess you're a Hollander ?
are you living in France ?

and welcome as a poster !

 

[BartW]

, the ability to accelerate and decelerate the tool is somewhat further down the priority list.

have no figures from the acceleration,
but the electric stabs specs say 80°/sec rotation speed,
perhaps you have / know the rot speed specs from the hydraulic stabs ?


just booked a flight to Pisa next week (to the new CMC offices)
so all input / questions / concerns are welcome.

 

[MapisM]

No it doesn't achieve the same effect. Sure it has the same effect while it's doing its thing, but but if it moves faster it moves for less time. (Because, all fin stabs at anchor have a stroke limitation of about +/-45 degrees). This is the whole point: a smaller+faster fin is more susceptible to running out of effect before the wave has finished than a slower moving fin, and therefore it doesn't achieve the same effect so far as stabilisation of the boat is concerned, AOTBE, except in small waves of course.

Fine theory, but I'm still missing the reason why CMC doesn't simply fit fins as big as their hydraulic competitors?!?
Then again, on second thought, forget my question.
You can probably find some good reason why at CMC they like to underperform, anyway.
And also myself, I've sort of lost the will to live, in this too obviously biased debate.
Let me follow a completely different approach instead.

You might remember the VdV thread, where many folks - yourself included - were fearing that the forum would have been overwhelmed by builders posting build threads, spoiling the "more catholic than the pope" opinions posted by all of us:
http://www.ybw.com/forums/showthread.php?327013
In that occasion, I offered (post #118) to put some money on my prediction that no mainstream builder would have followed the VdV route.
But unfortunately, nobody accepted to bet.

Now, my prediction is that at Sleipner, with regard to stabs, they have a brilliant future behind them.
To the point that, since you are indeed a smart buyer after all, we will all hear more about CMC stabs from yourself by the time you will spec them for the installation on M3.
Wanna bet?
See, I'm confident enough in your ability to make the right choices when it really matters, to offer to bet on something which depends entirely on yourself.
I could even go as far as offering to bet our own boats...

 

[jfm]

have no figures from the acceleration,
but the electric stabs specs say 80°/sec rotation speed,
perhaps you have / know the rot speed specs from the hydraulic stabs ?

Speed and acceleration are utterly different things BartW. High speed in actual operation (at anchor) isn't a virtue: it's an alarm bell. Assuming+/- 40deg angular stroke, which is about right, 80deg per second means the whole show is all over after just one second. For the rest of the wave period, you have no stabilisers.

Just to be clear, I think this is a great project for BA. I'm merely seeking to cut through the apparent marketing BS and suggesting you question them hard about whether the different properties of an electric motor+gearbox are really enough to make up for having only 60% of the fin area compared with ABT Trac, Naiad and Sleipner. Don't believe something so counter-intuitive just because they say it; dig deeper. Obviously this is only relevant at anchor; underway at 20kts 1msq or 0.6 will both keep the boat flat as a flat thing.

 

[BartW]

To move the hydruaulics you move a tiny-weight solenoid valve about 30mm and bang, they're out of the blocks. The hydraulic pump was already running and has forgotten what blocks look like, and the pressure reservoir was already charged up. Think about the vibrating feel on your brake pedal with ABS - that is a hydruaulic valve opening and shutting, and your brake calipers opening/closing, multiple times a second. Do you think that could be done better with an electric motor and gearbox moving the calipers in/out?

Each Tuesday evening I have my dive club training here in the swimmingpool in town, my hair is still wet.

For the most efficient fin movement, we teach the new divers they have to start the downwards fin movement slowly, and gradually increase the speed of the fins.
when moving your fins uncontrolled, and too fast,
the efficiency is less due to turbelences around the fin,

I'm not sure if this has anything to do with boat stabilizers, but just thought about it

 

[petem]

JFM and Mario, your knowledge of these matters and each of your certainty of being in the right is making this a fascinating debate (would be a shame if it soured a friendship though). Perhaps you need to employ an independent Hydro dynamicist (is that the right skillset?) to settle the argument (assuming you'll bide by his findings). Maybe loser pays fees?

 

[MapisM]

would be a shame if it soured a friendship though

Naaah, it was all in good spirit from my part, and I hope/think the same goes for jfm.
In fact, I wouldn't have been so transparent/ironic/straightforward/challenging (you name it, possibly also a bit annoying at times) if it weren't that I knew how clever my interlocutor is.

But re. paying anyone else for a settlement, not a chance. We would end up arguing with his findings anyway!

And at the end of the day, time will tell. ATM, none of us have any hands on experience on the specific equipment which is being debated.
BartW will soon be able to teach a lot to all of us, I guess.

 

[henryf]

Once again the benefit of my total lack of knowledge

If I was going to fit stabilisers there are a number of people who have gone down the road previously. In some cases it might be possible to give them a test run by visiting the owners on their respective boats. In other cases there are videos and I could always ask the question, "are they any good?" A word of warning here though, having spent a fair chunk of money owners will likely praise their respective brands regardless otherwise they look silly for having spent the money.

There is one person who is particularly interesting. Some say odd, his Mummy says special and that's JFM. He has specified more than one set of stabilisers so if the first set were a let down he could have gone back to the drawing board. I know he doesn't like to spend time researching things that go on his boats but........

So for that reason I would listen to John particularly carefully on this one. Not to the exclusion of everyone else but he is in a rather unique position.

If another manufacturer came on the scene with an as yet unproven solution but they seemed sensible I would take a view especially on price. If it was a great deal (they may be keen to get units out there of have a deal on an ordinarily more expensive model) then I might be tempted to take a punt. I suspect we are debating along the lines of good or best rather than rubbish or good. Any stabilisation has to be better than no stabilisation.

Henry

 

[rafiki_]

I disagree with this Rafiki,
the hydraulic systems I've seen in boats are simple valve controlled systems,
which can just be switched on and off (AFAIK)

a typical feature of a brusless DC motor (as used in this stab system) is that the electric current is controlled by a processer, which has very accurate controll over speed, power, acceleration,.... as you might have seen using in Robots.
No high precision robot is driven by hydraulics now aday's, but mostly by processor controlled electric DC motors, (AFAIK)
moreover there is a very accurate gear in there, with a huge reduction ratio, = very large lever arm.

Bart, there is no reason why an hydraulic device cannot be microprocessor controlled, in the same way as an electric motor. My University project was just this subject, feedback and control of an hydraulic system. You wouldn't see a mobile robot hydraulically powered, as it needs a portable power pack, much easier with small electric motors. You do see robots in assembly plants, both hydraulically (if large power needed) and air powered. These are doing tasks that need hugely accurate positioning, with better reliability than electric motors. In JFM's Sq, there is plenty of room for the powerpack, and it runs the thrusters as well. As JFM states in his post, you have instantaneous power and action with hydraulic stabs, because the energy is stored in the accumulator, and needs no conversion. There is no start-up delay, nor losses through the transmission.
I'm not saying that electric motors won't suit your application better, and for retro installation I can quite understand why an electric system is easier, as there is no pump and accummulator to package, nor hydraulic lines and hoses.

 

[BartW]

Some more thoughts on the engineering issue’s,

Re heat of the electric motor,
Last weekend, I had a long conversation with a specialist on brushless DC motors, as used in a production plant in automation systems. Here’s a summary of what ‘s been said:
These electric motors are designed for that sort of applications, where they also need to be able to remain stationary.
Important features from these motors are:
- They have a very big reduction in the epicyclical gear, so that very little force from the motor, is needed for a big force on the shaft (a big lever arm)
- The electronic controller makes sure that the electrical current is controlled permanently during operation, so minimal current for required force (in big contrast to the old metal magnet, where It is always the max current that is switched on or off, so maximum heat dissipation)
-Rotors are made from a high Q neodymium permanent magnet, very high magnetic force in a compact size. This together with modern design (low electrical resistance of the stator) make these units very efficient.
- These motors are modern machines in contrast with traditional AC motors, they can get extremely hot without any damage. In Flemish this is called “Isolation class” is typically F, in traditional motors it is A or B, …. or C for some better models. Wich means they can get very hot during operation, without any damage.

Re. fin size,
I appears to me that all CMC electra fins are longer then their width, while some competitors have more sqare fins, perhaps there might be a difference in behaviour, compare again with my scuba fins, Abnea divers use these very long fins, for efficiency reasons.

Re. fins stationary in certain conditions (long wave example from Jfm, permanent list in MapisM example).
I realized that CMC might have misunderstood my question on the phone, because they answered that the fins don’t remain stationary;
but probably they didn’t consider these “special” circumstances, as described above. Perhaps they didn’t realize that we dig so deep in the subject ;-) , same for a few other questions, CMC underestimated the knowledge on here ,
Therefore I’m sad that so often in this thread is referred to Marketing BS, while imo it is just a lack of good communication either from myself or from a few young but clever engineers in Italy. This brings for me a unnecessary negative image on the brand and the product (again all imho)
No argument against questioning the engineering specs though ! thanks for all assitance on this, very valuable for me !!!

Next week Wednesday I’ll go to CMC and we will visit SL and maybe Azimuth aswell, to see a few “in build “examples of the “Stabilis electra” . And I will hopefully get the chance to discuss all remaining issues in detail,

 

[Deleted User YDKXO]

There is no start-up delay, nor losses through the transmission.

On the construction machines we deal with, we are told there is a 10ms delay between the processor sending the signal and the start of the hydraulic actuation so there is virtually no delay in a modern processor controlled hydraulic system. I think the fact that construction machines are invariably hydraulic tells you everything you need to know about hydraulics reliability. However, efficiency loss is another matter. The accepted wisdom is that a hydraulic system is only about 70% efficient in translating input power into output power so IMHO the efficiency loss is considerably higher than an electric motor driven system even with a big gearbox reduction. As you say, the big advantage of an electric motor driven stab system is ease of fitting and reduced space usage and, I'm assuming, cost, although I haven't seen any comparative costs for either system on this thread. Maybe after Bart has had his meeting and assuming he buys a system, you guys with hydraulic and gyro stab systems would be willing to give approx costs for your systems because it would be interesting to know how these compare against an electric system