Stabilizers for Blue Angel, engineering question

[MapisM]

My entirely unscientific reasoning relates to my flopper stoppers.

Nick, I actually think that your flopper stoppers - unsophisticated as they were - had one big advantage, i.e. the fact that they were exploiting a better leverage position, if compared to fins placed under the hull.
Surely not as much as paravanes, but along the same principle, if you see what I mean.
In other words, for any given final result, I would expect that fins should bear a higher specific load.
That said, +1 to all your other considerations!

 

[MapisM]

European warranty/support was 'better than the Italians gave'.

No interest at all in defending my compatriotes, but it's hard to believe that anyone can give better warranty assurances than the builder...?!?
I fully agree that for Bart it's worth checking, anyway.

 

[Groot T]

No interest at all in defending my compatriotes, but it's hard to believe that anyone can give better warranty assurances than the builder...?!?
I fully agree that for Bart it's worth checking, anyway.

Hay MampisM, I don't think they were referring to the builder at that point. I hadn't even mentioned the make of the boat.
The comments came from the skipper of the Moonen and I think he was talking about CMC direct or a CMC dealer in the Med, sorry for not making it clear.

T

 

[MapisM]

Ops, it's obviously my comment which wasn't clear enough.
By builder I meant the stabs builder, i.e. CMC, not Moonen.
Bart at the moment is in directly in contact with them, not with any Italian dealer/distributor.

 

[BartW]

After a few day’s delay due to circumstances, today I had a long and very interesting and comprehensive phone call with mr A.C., the director and one of the design engineers of CMC.
I will try to give an answer to some of the questions raised on here, but don’t take me on the perfect wording, nor the engineering details of this.

Regarding these electric drives,
These are very HQ units made by Mitsubishi, taken from the automation industry (Robots),
state of the art Brushless DC electric motors, Including the gearing, the shaft, the EM brake, all supplied as a complete unit, any self made additions.
The core of CMC’s design, is the control / processing software, and the fins,


Heat generation is not an issue, because the main source of heat here is friction in the gearing / mechanical parts of the electric motor.
Because of the very tight tolerances these units are build at, (Mr A.C. compares with a Swiss watch)
the “mechanical energy loss” is neglect-able.

The heat dissipation in the electric motors when in a fixed position, is not an issue, because they will never be “permanently” in a forced fixed position.
The control software will counter react on a “short wave roll detection” and create a fin reaction almost immediately, the fins won’t stay fixed in a lowered position.
The processing software will detect a differential in Roll force, and act accordingly.
The fins won’t react on a very slow roll movement, that’s not what they are aimed for.
Fe when you turn the rudder to make a huge long turn, normally the boat will heal to one side.
When these stabs are active, this healing won’t be much affected. The boat behaves almost the same.

Almost all of the installed CMC systems are placed in a water sealed enclosure, there is no ventilation.


The gearing between the shaft and the electric motor is done by a bevelled gear, and a very special, Epicyclical gear; one specifically designed for brushless DC motors, and also integral part of the Mitsubishi drive unit.
Also the EM brake is inside the electric motor, and is a original internal part. Its not a special version nor a add on.
This brake works as a standard EM brake; you need electric power to disengage.
Remember there is a big RPM reduction in the epicyclical gear, so the brake doesn’t need to give much force.
The EM brake is engaged when the system is switched off, or not in anchor or sailing mode.

The electric motor has two different position encoders, one is electronic, and the other is a mechanical.
That one is used as a “key” for emergency position detection when no electric power is available.


Each fin could in theory turn 360°



Electric drive fins can’t be compared with hydraulic fins, they behave differently .
CMC has experience with both ! At the moment they are selling 80 electric systems a year, and have over 200 installed el stab systems.

By using very accurate motion sensors, (3pcs) the system can have a much faster processing / control system.
The limit here is that the system would behave too “nervous”.
Using “Bigger size fins” is then a solution to damp the control system, but then reaction time is “slower”, and you would need more power.

The system for a SL72 uses 0.6m2 fins, and the system on a SL82 uses a 0.8m2 system.
All have the same model electric drive, so it would be easy to swap fins, but these setups give the optimum result.

There is minimal power needed to keep the fins in its neutral position. (that’s why it is the neutral position) neutral position is permanently adapted during navigation at different speeds, minimum drag, minimum force on the fins…
When the system is not operating, the EM brake is engaged.

when there is roll detection on the motion sensors, or when there is a force difference detected on the electric drives, that would create roll, the fins will counter react this and move accordingly.

The result of all these details, is that these electric fins are more efficient then hydraulic fins, that’s why there is comparably much lower power consumption.



Mr A.C. invited me to the new factory in Piza, and visit together a few nearby yards that fit these systems. (ao SL iirc) If somebody on here is interested to join, and go there to discuss about some engineering details, pls give a sign, we could go there together.


Now back to Blue Angel;

For the hull reinforcement, mr A.C. agrees that there is not much more involved then adding some layers of GRP, as he also believes that Older Canados hulls are usually much stronger and heavier then more modern similar boats, where reducing weight is a key feature.

When I’ve accurate dimensions, we will know if BA is comparable to SL72 or SL82, but we are almost shure it’s the SL72.
CMC agrees that a length positioning close to the CGA is good, but there is a bit of flexibility on that.
I’m now at the boat, and first impression is that our estimated position in Bathroom and Dressing room is perfectly doable and accessible.
So lets go on with our investigations…
TBCont.

 

[BartW]

I had an E-mail this morning with a glowing recommendation for a company based in the UK. Apparently they did all the calculations, etc etc. Took all the pain out of the experiance, furthermore the price and European warranty/support was 'better than the Italians gave'. Take from that what you wish.

Toby, thanks for your assistance / sugestion,
at the moment I have enough input and help from different party's, and from CMC directly, which is alway's the best imo.
if I think I can use other sources of assistance, will let you know,
thanks again.

 

[BartW]

Bart

I can't add to the complex engineering debate (forgotten more than I ever knew to start with!), but it seems to me that the loads required to counter boat roll may not be as great as one would first think. My entirely unscientific reasoning relates to my flopper stoppers. They had a x-sect area of about a metre each, and four of them hung off the side cleats reduced boat roll by about a quarter on a 60' boat. I was surprised that I could comfortably hold one of them on the upward stroke (ie. under load) even in a quite significant swell. In other words, the load I could hold with my bare hands was able to reduce boat roll by a fair few percent.

Of course your application needs engineering analysis, not "my mate reckons..", and there are far more complex loads and fatiguing to consider, but if the calcs suggest less reinforcing is required than you intuitively expected, then I wouldn't be that surprised, and this may mean that you don't need to cut away the existing structural members in the hull and/or could get away with wooden reinforcement.

It sounds a great project, looking forward to hearing more.

Hi Nick,
Last season I considered flopper stoppers, for here in Toulon, for reducing the roll from the passing transfer boats.
I even prepared a new thread for that, but never posted, and cancelled the idea , don’t fancy the hassle.....

Yes I believe that quite a few mates on here think that the retrofit of stabs on BA is not a big deal regarding hull strength, we just need a “objective” confirmation.
And your feeling about the size of the forces involved is more or less confirmed during my conversation with CMC today.

 

[vas]

Bart,

interesting argumentation by the CMC guy.
NOT convinced on a few of them (heat fe, imho he's talking b*ll**** marketing speak...) but seems that overall is a decent system and I think you should go ahead (after all it's not my money, so why not )

regarding the hullthickness measurement, I had an idea for a single dive solution, bare with me:

Find the straight through seacock.
Remove pipe.
get someone to "blank" the pipe with a piece of rubbery thing on a strong flat surface (a plate would do, or a piece of wood, or plywood)
that soneone, pushes the flat surface on the seacock, and opens the seacock.
no water comes in obviously, while you dive and use moms knitting needle to measure the distance from the flat blanking plate your mate is holding against the seacock and the hull.
come up,
mate closes seacock and wipes the half a glassfull of water
measure the distance inside from the flat seacock face to the inner hull surface.
subtract from the needle length, got the thickness

if I were you, I'd take BA out of the port and do the measurement in clean waters

cheers

V.

 

[MapisM]

I’m now at the boat, and first impression is that our estimated position in Bathroom and Dressing room is perfectly doable and accessible.
So lets go on with our investigations…
TBCont.

Now, why do I have a funny feeling that BA will soon join the stabilised boating bandwagon...?

There's one thing I don't understand, though.
Why shouldn't the stabs contrast slow roll movements, and/or listing while steering?
Normally, one nice feature of stabs is that you can forget trim tabs to level the boat in strong crosswind or with an unbalanced load, because the stabs take care of that, regardless of the reasons which make the boat rolling or listing.
That's how my stabs work, anyway.
In fact, once I forgot to open the valves on the hoses interconnecting the 4 tanks while refueling, and as a result I had a 2 tons unbalance, with the boat visibly listing to stbd.
But right after leaving the dock, the boat listing disappeared, and I thought that it was just a matter of taking a bit of time for the diesel to flow through the pipes and balance between all tanks.
Only when the boat was listing again while mooring in the marina, I understood that she was level under way only thanks to the stabs. And eventually, I opened those valves, of course...
By the same token, also while steering, it's almost impossible to make my boat list, if the stabs are on.

Now, I understand that with a planing boat steering hard over at high speed, it can be better not to contrast too much the natural hull listing, because the hull could become less stable/predictable, and possibly not steer as much as it should.
But I would think that such risk is only relevant with fast sportboats, capable of 40+ knots.
On a heavy boat like BA, mainly meant for comfort rather than speed, if I had to choose between a level ride in all conditions and a slightly better steering capability when running at WOT, I wouldn't hesitate for a second.
Did AC tell you anything about the rationale for not "correcting" the above conditions?
In principle, I can't see any reason why their stabs shouldn't be able to cope with them, so it must be a design choice, but it doesn't seem very logic from my viewpoint.

Re. his invitation to see their factory, I would really like to join you (btw, Pisa is a very interesting town, well worth the trip in itself, if you've never been there), but when are you thinking to go?
By next week, I'll be flying to the other side of the Pond...

 

[BartW]

Did AC tell you anything about the rationale for not "correcting" the above conditions?
In principle, I can't see any reason why their stabs shouldn't be able to cope with them, so it must be a design choice, but it doesn't seem very logic from my viewpoint.

I don't think its a design choice,
as far as I could understand it has to do with the availability of very HQ specced moving sensor devices in combination with these quick reacting drives, so a better responding and more natural behaviour could be acheeved,

but again, I've no experience with stabs, and my comments might be not correct nor accurate,
so for those who like to discuss this in detail, I'll invite you to have a call with mr A.C. himself. Details available by PM



I think that MapisM can confirm that AC doesn't speak marketing BS ;-)

 

[Deleted User YDKXO]

OK, fair cop on the term mechanical energy. I gotta say in years of doing an engineering degree etc and checking with my father (chartered engineer) we have never heard the term. With respect and outside astronomy, it's a bit of schoolbook term. That britannica article was very dumbed down and lacking precision in its concepts, but no worries. Anyway no disagreement here; just semantics

Never heard the term 'mechanical energy' during my engineering (civil) degree either just, as you say, potential and kinetic energy. Maybe this is a modern educational concept and we're just betraying our advanced years?

 

[MapisM]

I think that MapisM can confirm that AC doesn't speak marketing BS

Yep, he definitely isn't a marketing man. Rather the opposite, in fact.
Otoh, I rest my case on being more logical to level the boat also if and when there's a constant listing, for whatever reason.
The fact that he stressed the sensor movements make me guess that maybe they don't use also a gyroscope (or any other device meant to sense also the static boat level).
Obviously, if the system only reacts to the hull movements, it means that if the boat, as in my previous example, is just listing in flat water due to an unbalanced load, the stabs do nothing to correct that.
I'm just wondering why. It only takes a very tiny adjustment of the fins position, to contrast such "static" listing, while under way.
And the same goes for steering-induced listing.

 

[MapisM]

Never heard the term 'mechanical energy' during my engineering (civil) degree

Oi folks, gimme a break.
I posted a link confirming that the term is used to mean potential + kinetic.
These days, whatever the web says is the truth, you know....

 

[Pinnacle]

Now, why do I have a funny feeling that BA will soon join the stabilised boating bandwagon...?

That will be cos its gonna happen!

 

[jfm]

Interesting stuff BartW. 80 installed units is encouraging. And it's good to answer the curiosity about the EM brake.

I find some of the above impluusible and you would want to cross examine Mr AC, but you can do that or just trust that these things will work, which no doubt they will

For example "they will never be 'permanently' in a forced fixed position" makes no sense to me. Why not, if there is a big swell or a cross wind?

And my "big swell" analysis above was merely a subset of the whole ecosystem: in a medium/normal swell as the fins sweep from side to side the heat generated as the fin pushes against the waterflow is the same. I mean, as the fin sweeps from side to side underway the amount of work done on the hull/water by the electric motor is tiny: most of the electrical energy goes to heat. Maybe CMC can manage (dissipate) the heat perfectly well, which is great, but to say the heat isn't generated to begin with is nonsense.

The statement "main source of heat here is friction in the gearing / mechanical parts of the electric motor" is from an engineering/physics point of view absurd and utterly wrong. If the only energy requirement were what is needed to overcome the swiss watch friction in the gearbox and the work done by the fins on the hull+water, the electric motor would be tiny. AC seems completely to miss the point that the function of a stab actuator here is to create a torque, not do work, and creating a torque without work means, as any engineer can tell you, you must turn ALL the elctrical energy into heat. Just as ALL the electrical energy consumed in my magnet crane holding up a tonne of steel for an hour goes to heat, and absolutely none of the electrical energy goes to work done on the tonne of steel.

As I say, if they dissipate the heat then great. But denying its creation to begin with is nonsense

The other stand out bit for me was "Using “Bigger size fins” is then a solution to damp the control system, but then reaction time is “slower”, and you would need more power". Now that really is BS! It is just beyond any doubt that bigger fins work better at anchor, and that's why you have them. Of course you don't need them underway, esp on a 20kt fast boat like BA. To say the reason for larger fins is "to damp the control system" is garbage, ffs! MapisM, where is your flag? And sure you need more power with bigger fins, but you have unlimited power on a hydraulic boat. The only people who are worried about needing power in this context are those that have a problem with heat.

My take is that CMC have accepted a system that is less good at anchor than the 1msq category because their gear cannot drive 1msq, and that's a trade off for the easier install of electric units, and of course that is a perfectly sensible trade off and one worth making on BA. So I'm 100% supporting you in this project and its great benefits on BA, but let's call a spade a spade when it comes to marketing BS

 

[MapisM]

80 installed units is encouraging.

J, actually 80 is the current yearly number, with 200+ already installed since they were introduced. And strictly on boats from 72' upward.
I'd rather call it impressive, than encouraging.

To say the reason for larger fins is "to damp the control system" is garbage, ffs! MapisM, where is your flag?

LOL, I see your point, and frankly the same thought sprung to my mind after quickly reading the update from Bart, particularly re. heating - not so much re. fins size though, and I'll explain why.
But after re-reading it carefully (and based also on a phone chat that I had at the beginning of all this with Mr.AC), my only concern, albeit not so minor, remains the one I already posted, related to the capability to keep the boat steadily levelled in any conditions.

Let's separate the two points, which are completely different and somewhat unrelated.

1) heat:
At first, I also understood Bart's statement "the main source of heat here is friction in the gearing / mechanical parts of the electric motor" as equivalent to "friction in the gearbox", to use your wording.
But coming to think of it, I would instead guess that AC meant something different - i.e. that all the mechanic components of the electric motor itself are built to extremely high standards, to make it working as close to 100% efficiency as it can get. And the other point which transpires from Bart post is that, according to AC, the heat can only be due to system losses/frictions, etc. Therefore, an "ideal" motor with no losses should do its job producing zero heat.

And in fact, I'm not so sure that your explanations of the reason why an electric motor just MUST generate heat are correct - or that they aren't missing something, anyway.
Apologies for using a layman's wording now, but at the end of the day an electric motor isn't just a machine meant to transform electricity in magnetism, and in turn this magnetism is used to spin a rotor/shaft?
Now, of course I understand that this can't happen with zero losses, but if it would, couldn't we think that 100% of the electricity is fully converted into a magnetic field?
And at that point, whether that magnetic field is used to rotate a shaft, or just to keep it steady against some resisting forces, it shouldn't make much difference.
The same reasoning applies to your magnet crane example, btw.
Mind, I'm not arguing against the "work = force x distance" principle, and TBH I can't explain why it shouldn't apply in this case, but my mix of gut feeling and common sense tells me that for some reason it doesn't.

Incidentally, as I understood, most CMC installation were made in pretty small and w/tight compartments.
And if so, I can't think of a worse environment where to run for hours something which generates a significant heat, without entering into a loophole which is bound to melt everything, rather sooner than later.
Nah, there must be a good reason why the heat created by these things is close enough to zero, to become practically irrelevant.
We just happen to not understand exactly what this reason is, but there must be a scientific one.

2) fins size:
I agree that the statement about bigger fins being a "solution to damp the control system" doesn't make a lot of sense. TBH, I'm not even sure to understand what it means...
...but I suppose something got lost in translation here. Let's forget that for the moment.
Based also on what AC told me when we spoke, my understanding (which can still be wrong of course, but hopefully not for language reasons alone...) is that in their tests at zero speed CMC noticed that a prompt response to a sudden rolling movement, together with a fast angular fins speed, are key factors - even more than the brute force of a bigger fin surface.
And in that respect (promptness and speed, together with a higher max rotation) their system outperforms hydraulic stabs.
We even discussed the most typical scenario of zero speed stabilization: boat steady as a rock, anchored in a quiet bay. Suddenly, out of the blue (LOL, can you think of a more appropriate use of this expression? ), a series of navigation wakes hits the hull. In the worst case, depending on the frequency of these waves and on the size (plus shape, etc.) of the anchored boat, the roll can even increase progressively.
Now, in this scenario, according to AC (but I also see a logic in that), the more immediate and faster the very first fins reaction is, the lower the effort required to keep the boat stable, also against the following wakes.
Then again, proof and pudding are the words which spring to mind...
...I can already see BA and M2 anchored in the same bay this summer, with high precision inclinometers installed onboard!

Last but not least, ...

My take is that CMC have accepted a system that is less good at anchor than the 1msq category because their gear cannot drive 1msq, and that's a trade off for the easier install of electric units, and of course that is a perfectly sensible trade off and one worth making on BA.

Nah, I really don't think that the average Joe who buys a SL, a Benetti or a Moonen is willing to compromise on zero speed stabilization.
If their performance wasn't at least on par with hydraulic stabs, I don't think they would have been choosen as OEM installation by any of these yards.
Also because the installation problems which almost rule out hydraulic stabs in retrofitting installations, as in BA, do not exist with new builds. Or they are much less critical, anyway.
In spite of that, they are now mostly supplying their stabs to builders, rather than for retrofit on used boats.

 

[Deleted User YDKXO]

At first, I also understood Bart's statement "the main source of heat here is friction in the gearing / mechanical parts of the electric motor" as equivalent to "friction in the gearbox", to use your wording.
But coming to think of it, I would instead guess that AC meant something different - i.e. that all the mechanic components of the electric motor itself are built to extremely high standards, to make it working as close to 100% efficiency as it can get. And the other point which transpires from Bart post is that, according to AC, the heat can only be due to system losses/frictions, etc. Therefore, an "ideal" motor with no losses should do its job producing zero heat.

And in fact, I'm not so sure that your explanations of the reason why an electric motor just MUST generate heat are correct - or that they aren't missing something, anyway.

All kinds of engines generate heat (and noise/vibration) because they're not 100% efficient at converting their input energy into output energy. A quick wiki reveals that brushless motors typically have efficiencies of 85-90% which is pretty damned good but still 10-15% of the energy generated is lost, probably mainly in heat generated so I don't think it's true to say that the motors CMC use don't generate any heat, probably more likely that they don't generate enough heat such that CMC have experienced any problems on their installations so far. As for the heat generated by the gearbox, yes it's true to say that there must be a big reduction; I don't know what speed the electric motor runs at but possibly 1500rpm. But according to Bart CMC use a special epicyclic gearbox which again AFAIK have very high efficiencies 95%+. Just my fourpennyworth but I still bet that the electric motor is the main source of heat

 

[MapisM]

I don't think it's true to say that the motors CMC use don't generate any heat, probably more likely that they don't generate enough heat such that CMC have experienced any problems on their installations so far.

Agreed 100%.
My statement which you quoted was related to jfm example according to which, in some conditions, the electricity goes ENTIRELY into heat.
That just hurts common sense...

 

[vas]

Agreed 100%.
My statement which you quoted was related to jfm example according to which, in some conditions, the electricity goes ENTIRELY into heat.
That just hurts common sense...

and that's exactly what made me say that this guy is talking marketing BS...
or he doesn't know what he's talking about.
Either options are dangerous and i'd not want to deal with him.

V.

 

[MapisM]

Huh? I don't think that's fair, V.
Nobody ever said - CMC included - that electric motors don't generate heat at all.
As I understand, they just tried to explain why the answer to the question about whether heat is an issue or not is no.
What lead you to think the opposite?