Fin stabilisers with curved fins, new from Sleipner, 50-60 foot boat bracket

[vas]

Crazy thought, if you did swop to the curved, would it be worth getting in touch with the owners of Match 1?
Or a less Crazy thought, just put Match 3 next to Match 2...

doubt it's going to materialise as M1 iirc is somewhere in Sweden and M3 looks like is going to be a D hull

V.

 

[Robg71]

Claims that by now some of us have had the opportunity to try and test. And you weren't even joking.
OTOH, I note that by now you feel obliged to specify to Robg71 that Sleipner "will have hydraulic actuation only for foreseeable future".


Also that Sleipner answer emails quickly and efficiently.... CMC still have not answered any emails i have sent. They didnt even get over the first hurdle for me. Sleipner are introducing a smaller actuator next year too. Its a one stop shop for all my requirements, considering i specefied hydraulics to start with. Thrusters, fins and windlass. System synergy for me plays a big part.

 

[jfm]

Mapis I'll try to respond, but keep the wordcount short

Well, maybe those readers don't remember when you tagged as "marketing BS" the CMC claims on fins size and motors heat.
Claims that by now some of us have had the opportunity to try and test. And you weren't even joking.

They don't remember it because it never happened, but never let the truth get in the way of a good rant, eh? What I said to BartW as regards heat was "Please check with CMC that they have managed the heat". (It turns out they have, which is great). BartW reported that CMC said "our actuators don't overheat because our gearboxes are like Swiss watches". I said THAT was marketing BS, because the heat is the motor winding not the g'box. (You may not see that: you didn't/don't understand the energy transfers in electro magnetism to begin with)

As regards fin size, I said to BartW that 0.6msq is too small for such a large boat as BA. I still think that. You say "some of us have had the opportunity to try and test" but with respect, none of you have any other experience of STAR. As you know, I have been on BA at anchor too. Just look at the video below. Stabs working quite hard, full stroke, reasonably fast, perhaps 65-75% of their max impulse. Then the camera pans up and ... there are no waves. The flattest anchorage ever! Fact is, 0.6m sq isn't really big enough for this boat, for STAR use, imho. The 0.6m2 will take out some roll, but they hit their limit much sooner than 1m2 and will not cure bigger stuff that you do find in anchorages, eg large wake of passing boats etc. The video says it all...

Superiority which is so obvious that it's not even worth explaining it, not just for retrofits, but also for new builds.

"Superiority" is a big topic, and not at all obvious. Lots of factors.

(a) Electric is easier to fit and cheaper to fit, new build + retrofit. That is obvious! It therefore has a big future, though as CMC have a patent they are the only suppliers at least now.
(b) As regards stabilisation, electric/hydraulic seem the same with no obvious difference. CMC claim their electric actuation actuates better. They told BartW and wrote in their patent applic, I believe, that they can achieve 80 degrees per second. But in fact, and CMC didn't know, my Sleipners do 84 deg/second. I showed the data on here ages ago. Now when you add curved fins, the "superior" thing involves another factor. Electric is superior for installation, hence perfect for BA as a retrofit especially, but the overall stabilisation from the curved fin is better, and right now that means hydraulic, so curved Sleipners are superior, but it's not because they are hydraulic that they're superior, if you see what I mean
(c) Noise. This is in the ear of the beholder but many buyers will not be able to live with the noise of electric actuators inside the boat. The gearbox whine, I mean. It is a significantly louder, and more annoying, noise than hydraulic. Each customer needs to make his/her on choice on this.

Well, "Detailed info", and found this ad in the first page:

Agreed - that page is marketing BS!

is that a pro or a con, in a joke?

It's a con, mate

beggars belief that such already fantastic results can be further improved, let alone by 50%

Ah come on. Do you remember about 35 years ago Princess launched 37 fly with "this is the biggest boat we will ever make; we cannot see customers wanting bigger". Stabilisers are fantastic, but there is room for improvement as in all engineering. The benefit can be smaller fins (less drag) yet still same or slightly improved STAR. I agree that straight fins are already v good, so I would swap 1m2 flat fins for say 0.8m2 curved, and get more NmS (but not 50% ) and less drag. Lots of choice here for the customer

"... you're accusing me to have not been objective, in fact."

I apologise. "Objective" was, I can now see, the wrong word. All I meant was, ref the Garfield thing, "please stick to the topic; go for the ball not the man."

It's the relevancy of the "side effects" which simply isn't reflected at all in my practical experience.
Under no circumstances, either at anchor or under way, I ever had the faintest perception of fins-driven sway and jaw effects.
For sway, while I accept that in principle the effect could be there, I never felt it while onboard a stabbed boat. Not one iota.
In fact, just think of how much power it takes, running both bow and stern thruster together, to start a sideways movement of the whole boat.
And then compare that with the stabs power, considering also that as a mean of transferring power to the water for a sideway movement, fins are obviously less efficient than thrusters.
Even if the fins would be placed vertically along the keel, one at the bow and the other astern, the sideways movement of the whole boat that they could generate with a single sweep is just a tiny fraction of what the thrusters can create in the same timeframe.Bottom line: in which planet and with which boat did Sleipner practically experience the side effects that vector fins are supposed to cure?!?
Can you honestly tell to have ever noticed anything like that with Match, in the even slightest way?

You are missing the point MapisM, and your own "bowthruster" reasoning defeats your own conclusions. Yes in a BA or Match, you never feel much yaw or sway. But feeling it isn't the point. It is still there, and the energy consumed takes away from the energy that should be put into rotating the boat, and THAT is what curved fins cure.

Take Match as an example because I have the data. Bow+ stern thruster =50hp; stabs maximum STAR is 10hp, but more usually say 6hp. The stabs have nowhere near enough power to make the boat move appreciably (to a human) sideways, ie sway, even if mounted on the keel bow+stern, exactly as you say. BUT the power needed to roll the boat (to counter the roll induced by waves) is tiny compared to the thrusters: it's 6hp. If you waste a proportion of that, say 2hp, in swaying the boat you will not feel the sway but it is still energy lost, leaving 4hp to anti-roll the boat. If you change the direction of the force vector so that no work is done swaying the boat (that you can't feel anyway) and more work is done rotating it, you have improved the NmS value appreciably. The CFD shows a 50% increase (in NmS terms), ie in the order of 2hp, and I repeat that you will not feel any elimination of sway because you cant feel 2hp of sway to begin with, but you will feel it in improved stab performance because it is a ~50% increase in the NmS value. Your "on which planet" Q entirely misses the point

In my posts above I never claimed the reduction of perceptible sway was a benefit of Vector fins in larger boats eg BA and Match. I said it was a perceptible benefit in small/light boats ie 50 footers or so. In these boats the bowthruster is I think around 7-8hp and so something in the order of 2hp sway reduction IS perceptible, I think. Time will tell - I haven't been on a 50 footer light boat with STAR fins and neither has anyone else afaik! Anyway, look, if I'm wrong about the elimination of perceptible sway in light boats, it doesn't matter. It was never the main event anyway; it is a mere sideshow. The main event here is ~50% increase (in NmS terms) of the antiroll

Point 7:
Obviously I can only take your words for the results of CFD models, but it's hard to think of any logic reason why the scoop effect shouldn't be symmetrical.
And also the 23% improvement on the "positive" side sounds like a helluva lot, also because the curvature is along the height, not the length of the fin.

I cannot comment on that other than to say your engineering intuition needs recalibrating!
As regards oars, there are big differences between designing a fin and an oar blade (due in part to the high STW of the rowing boat thru the water) but we will drift off into complex fluids stuff so I propose we don't go there
Continue in next post....

 

[jfm]

Continuing last post....

Point 8:
"the absence of such a test isn't a reason to bash Sleipner"
Well, of course it is. I mean, not the test absence as such. But if they don't have two AOTBE boats to make the test, they should refrain from making claims on improvement of curved vs. straight, at least till they will have such tests.

That's nonsense, but only imho of course. Simple intuition tells you the curved fin is better. The vector diagram that Sleipner publish helps you get a sense of the scale of the benefit. The Princess 56 data is outsntading compared to results we normally see from straight finned boats. The CFD analysis computes the answer in NmS terms. If you think Sleipner should just say silent, then let's just agree to differ.

Point 9:
I already acknowledged that the vector is unaffected by the distance from the keel, on a P hull. No need to ask Newton an opinion on that.
But ideally, the fins shafts should still be pointing as much as possible towards the roll axis, shouldn't they? You already acknowledged that in your post #28, as I understood.
And by moving the fins towards the keel, there must be a point where the shafts will point exactly towards the roll axis, obviously.

No, they don't need to point towards the axis. When I said that (though I don't recall and haven't re-read my post so sorry if I didn't say it correctly) I was talking in context of Nick-H's theoretical cylindrical. The fin shaft needs merely to be parallel to a radius of the roll axis, and perpendicular to a tangent of that radius, in an ideal world, on a boat with a perfect steel-set-in-rock roll axis.

Point 9:
Otoh, just bring this to the extreme: don't you agree that if the fins would be placed along the keel, straight vertical fins would be more effective than any curved fins?

Absolutely not. Straight fins on the keel would waste the maximum possible energy in sway+yaw. You might not feel that as the fins are only 6hp anyway and the boat will have some roll axis stiffness. Now, if you put curved fins onto the keel, they would produce the same force vector as a flat fin mounted on the deadrise at say 20degrees, so would intrinsically waste less energy in sway by having a higher vertical component of their force, resulting in a higher NmS of antiroll torque AOTBE. (Umm, the fact you even ask this question tells me you're not getting the vectors, MapisM...)

Point 10:
the "% improvement" figures quoted by Sleipner are the anti roll work figures derived from the CFD modelling, not the degrees of roll
Well, I'm afraid this is a confirmation of what I'm saying, i.e that these numbers, as they are used in the context of the leaflet, are nothing else than a prime example of marketing hype, being rather aimed at shouting "new and improved", than at informing the reader about something he/she can actually understand...

You are quite sour grapey to criticise them on this ground when they invent a product that increases the NmS value ~50%, which is a very fine achievement. Sure, when they get 2 identical boats with flat/curved fins in same anchorage they can measure and quote the degrees-of-roll improvement but until then we only have the princess 56 plus the CFD data to work on. You cannot seriously believe that a 50% increase in the NmS value wont result in an appreciable improvement in stabilisation, can you? It might not be 50% in degrees-of-roll terms on all boats, but surely some gut feel and the Princess 56 data tells you these curved fins are significant.

 

[MapisM]

Its a one stop shop for all my requirements, considering i specefied hydraulics to start with. Thrusters, fins and windlass. System synergy for me plays a big part.

Well, good for you then. But with these premises, why on earth did you bother asking CMC at all...?

 

[MapisM]

Mapis I'll try to respond, but keep the wordcount short

LOL, I'm afraid that in this respect your reply is a clear cut case of not living up to its premise!
Otoh, I saw this coming when I said that I can already see some interesting winter debates at the horizon, so I guess I can't complain, and I must find a bit of time to go through all your objections...
But not tonight. I spent most of my afternoon helping swmbo shopping and cooking for a dinner with some friends of ours, which lasted till a few minutes ago.
And needless to say, we did open a bottle or three of Carignano along the road.
So, a good sleep is now higher on my priorities list than debates on boat stabs...
Cheers for now, P.

 

[Robg71]

i believe you are in a fairly well argumentative mood.... so leave it at home.....
four weeks ago when i first emailed cmc there was no sleipner system to fit.....
good night ladies... x

 

[jfm]

why on earth did you bother asking CMC at all...?

MapisM, CMC make thrusters, stab fins (electric and hydraulic) and hydraulic packs that would run all those plus a windlass. So it seems perfectly sensible for Rob to invite them to send info for his project, surely

 

[BartW]

I didn’t intend to interferre on the discussion about all aspects on the vector fins,
But when there are conclusions on my own stab system, I feel need to react

As regards fin size,
I’m very surprised that from just this short film, and a short visit on the boat,
can be concluded that the fin size of my stabs is too small,
This is NOT serious ! imho.

I must admid that in that film you can’t see the swell,

but I just post these pics,
to show what kind of sea state there was around the corner
pictures taken approx one hour beforte the film, south of Pamplone beach,

The film was made during a lunch stop , east side of Cavalaire bay, to hide for the waves,
but a very long swell coming from the strong easterly storm in the middle of the ligurian sea,
was reaching this anchorage,

For me this film only prooves that despite the huge movement of the fins, the boat is hardly moving,
if there would not have been a strong swell, the boat would have been rolling like hell, due to such a big fin movement….

Now I agree that there is a limit on the swell that my fins can cope with on anker
we have discovered that limit,

On anchorages with many passing boats (fe Pamplonne beach) we hardly “EVER” reached the limit of the fins,
If the fins occasionally do a maximum excursion, the next period, they have again a smaller excursion, as waves come from all directions.
I was very impressed and surprised how good the system copes with waves from passing boats.

The anoying swell in Villefranche, now 2 or 3 weeks ago,
the fins could easily handle, much less movement then in the film, never reached the limit,
at night when we switched on the stabs, we could get back to sleep, boat very stable.

If there is a anchorage where the swell is over that limit,
or where the system would not be able to do a adequate stabilisation,
the fwd/aftwd tilt movement would be big anyhow,
and you would want to change anchorage anyway
we never had to do that yet.


There is one usage where the system sometimes struggles;
diving takes place very often in the open sea,
When divers are down, not anchored, boat free floating above the dive spot, no wind,
the boat tends to get parallel with the swell,
So when it is a strong and especially loooooong swell, Created by a storm far away,…
the system reaches its limits,

But even for that I don’t want to change the size of the fins,
Bigger fins would improve, but also have a limit…
If that occasionally happens I just slowly navigate around the dive spot, and due to the movement, and the different angles of passing the swell,
The system copes again perfectly
I would give my fins a 99% score, not 95%, but 99% !

My main and only argument against stab fins, was and still is the extra drag
CMC has exactly the same vieuw on this like myself, and I’m very pleased that my 0.6m2 fins have a 99% score,
And I would never put bigger fins, not 1m2, nor 0.8m2 to achieve 99.9%,
I can get bigger (0.8m2) fins from CMC, and my drives/system can run them,
but I don’t even want to test them, as we are so satisfied with the performance of what we have,
Pls asc our guests and asc Elly.

So I firmly disagree on the statements about BA’s fin size.


Back to vector fins,
I understand and accept the advantage / improved efficiency stated above
And much appreciation for the inventors / developers for that,
I think that this is a valuable improvement of a stab system, especially on smaller systems,
I wish them much succes with it, and we will probably see many boats with curved fins in the future,


By the way,
CMC is absolutely NOT interested in the sub 70ft boat segment for stab fins, and they don’t intend for the near future,
My boat was on the edge, I was lucky 
They are targeting and getting the majority of their business from the 35…50m boat segment, for now only/mainly in Italy (and Holland).

 

[MapisM]

i believe you are in a fairly well argumentative mood.... so leave it at home.....
four weeks ago when i first emailed cmc there was no sleipner system to fit.....
good night ladies... x

Whoa, and I would be the one in argumentative mood?
You're free to read my previous question as you wish of course, but I asked simply because I was struggling with your logic - and I still am, tbh.
No matter what was available from Sleipner 4 weeks ago, if you "specefied hydraulics to start with", CMC was the wrong supplier to contact, plain and simple.
I would have rather checked Sleipner offer against ABT, for instance.
And I don't get jfm comment either, because aside from the fact that afaik CMC does not even build hydraulic stabs anymore (which is something I accept you might not be aware of, by just looking at their website), it's adamant to anyone around here that CMC is THE electric stabs supplier.

That said, I'm not justifying the fact that they didn't answer your emails, obviously.
I think BartW experience so far is different though, considering just as an example that the CMC founder and one of his engineers drove from Tuscany to Antibes and back on the same day, just for a sea trial on BA...
Then again, generally speaking it's true that at CMC they don't seem really interested in small installations.
Imho it's a mistake, considering that many of their competitive advantages are even more relevant with small(ish) boats.
Otoh, as long as they're busy supplying electric stuff whose AVERAGE fin size is 2sqm, obviously they know better than myself...

Anyway, with apologies for going a bit o/t, did you already design the hydraulic systems on your new boat?
There are some logical implications to consider when going 100% hydraulic, like how to power the winches when the engines aren't running, as an example.
'fiuaskme, on a 50 footer I'd rather just push a button to spin a 24V winch, than turn on a genset, a VFD and a 3-phase motor, to eventually move an hydraulic pump...
All the very best for your project, anyhow!
I for one am surely looking at your build thread with great interest.

 

[BartW]

MapisM, CMC make thrusters, stab fins (electric and hydraulic) and hydraulic packs that would run all those plus a windlass. So it seems perfectly sensible for Rob to invite them to send info for his project, surely

CMC doesn't make systems for boats below 70ft,
on the webside can be seen that their smallest bow thruster has a diameter of 30cm !
hydrailic systems are almost completely stopped,
so a enquiery for a self buyld 50ft project might have been ignored
(don't know for sure, I didn't asc)


with due respect from myself for Rob's interesting and challenge-ing project !!!

 

[BartW]

Then again, generally speaking it's true that at CMC they don't seem really interested in small installations.
Imho it's a mistake, considering that many of their competitive advantages are even more relevant with small(ish) boats.
Otoh, as long as they're busy supplying electric stuff whose AVERAGE fin size is 2sqm, obviously they know better than myself...

I had this argument with CMC AC long ago, and again this week, and he answered that
"they are basically a engineering company, more focussed on the technology,
aimed in first instance at the closeby home market, and 35-50ft range of boats.
For the 50ft-70ft range market they would need a totally different organisation,
and thats not their intention on a short term,
they want to grow with the right timing"

 

[MapisM]

They don't remember it because it never happened, but never let the truth get in the way of a good rant, eh? What I said to BartW as regards heat was "Please check with CMC that they have managed the heat". (It turns out they have, which is great). BartW reported that CMC said "our actuators don't overheat because our gearboxes are like Swiss watches". I said THAT was marketing BS, because the heat is the motor winding not the g'box. (You may not see that: you didn't/don't understand the energy transfers in electro magnetism to begin with)

Oi, and you accused ME to not be getting the ball so going for the man?
Not that it really matters, because we know by now that at Mitsubishi there must be someone who understands all that MUCH better than both of us together, and multiplied by three for good measure.
That aside, c'mon J, let's be serious. I neither have the time nor the interest to re-check all the wordings of that thread, but you know it's unfair to label my previous comment as just a rant.
In fact, I remember perfectly that at some point BartW even felt the need to apologise for what he could have misunderstood from CMC, after most of his explanations were repeatedly bashed as marketing BS.
Otoh, just throw the string "marketing BS" site:www.ybw.com into Google, and see how many pages of that thread you get in return.
Though incidentally, the first occurrence now points to this thread, in a sort of biblical nemesis...
Oh well, whatever. Let's agree to disagree on this, it has zero relevance for the debate anyhow.

As regards fin size, I said to BartW that 0.6msq is too small for such a large boat as BA. I still think that. You say "some of us have had the opportunity to try and test" but with respect, none of you have any other experience of STAR. As you know, I have been on BA at anchor too. Just look at the video below. Stabs working quite hard, full stroke, reasonably fast, perhaps 65-75% of their max impulse. Then the camera pans up and ... there are no waves. The flattest anchorage ever! Fact is, 0.6m sq isn't really big enough for this boat, for STAR use, imho. The 0.6m2 will take out some roll, but they hit their limit much sooner than 1m2 and will not cure bigger stuff that you do find in anchorages, eg large wake of passing boats etc. The video says it all...

Two points here:

1) Re. none of the FDC crew members having any other STAR experience, how can you say that - no matter how respectfully?
We stayed together for one week, but I never asked anyone if they ever tried any other stabbed boat before.
So, for all I know, each of them could have spent months at anchor with zero speed stabs.
Mind, not that I think they have, but I would never dare labelling their experience (or lack of) without knowing what I'm talking about.
Otoh, speaking of myself, indeed my STAR experience is small, if compared to a dozen of years which I spent on my own boat, whose humble stabs are "only" working while cruising.
But aside from BA, I had the opportunity to experience the behaviour of a couple of ABT STAR equipped boats (incidentally in the same size bracket of Match and BA), a much bigger one with Naiad, and a 60' or so boat with Koopnautic.
And in all of them, bar none, the effectiveness was always impressive - and surely good enough for the job they were meant to accomplish. Exactly as it is in BA.
I honestly think that the differences between each boat were much more related to the different sizes/hull types, rather than to the different stab equipments.
The bigger and heavier boat, with a pure D hull, high draft and deep keel, was indeed a bit more stable than all others.
But pretending on that basis that Naiad are better than the others would be ridiculous.

2) Re. "the video says it all", also BartW already said it all, and I can only second each and every point he made.
I wil just add a comment of a very experienced boater, with his own wording, taken straight from the Sleipner testimonial video (video which could well be a great competitor in a "flattest anchorage ever" context):
If you look at the anchorage we're in now, it's kinda typical, in a photograph this would look very calm, but there is actually a gentle swell coming through the anchorage...
Now jfm, doesn't "deux poids, deux mesures" spring to mind...?

the overall stabilisation from the curved fin is better

So far, that's your opinion. A respectable one, but still an opinion.
I'm afraid only independent tests carried out on AOTBE boats, one equipped with straight and the other one with curved fins could confirm/deny that.

It's a con, mate

LOL, easy tiger! That was just a joke on my own joke (a metajoke, if such wording makes any sense in EN), though possibly even weaker than the first one
Here, I made it again. A meta-metajoke...
Oh well, forget all that. Sense of humour is obviously subjective, no right or wrong here.

In my posts above I never claimed the reduction of perceptible sway was a benefit of Vector fins in larger boats eg BA and Match. I said it was a perceptible benefit in small/light boats ie 50 footers or so. In these boats the bowthruster is I think around 7-8hp and so something in the order of 2hp sway reduction IS perceptible, I think. Time will tell - I haven't been on a 50 footer light boat with STAR fins and neither has anyone else afaik! Anyway, look, if I'm wrong about the elimination of perceptible sway in light boats, it doesn't matter. It was never the main event anyway; it is a mere sideshow.
The main event here is ~50% increase (in NmS terms) of the antiroll

Hang on a minute.
Sleipner actually suggests that the "side effects" are relevant for boats in the 15-22m bracket, which isn't that far from Match and BA.
But that aside, it's much more interesting to hear of your agreement on the principle that sway is not a perceivable problem.
Now, if that is true - and I couldn't agree more - why is Sleipner selling the thing as a "permanent seasickness cure", rather than a mean of improving efficiency, increasing NmS, or whatever?
In my books, that's not even in the marketing BS realm anymore.
I know exactly how it would be called in IT, but I'm not positive about the EN translation.
"Fraudulent representation", maybe? I'll leave this to you, I'm sure you know better.

No, they don't need to point towards the axis. When I said that (though I don't recall and haven't re-read my post so sorry if I didn't say it correctly) I was talking in context of Nick-H's theoretical cylindrical.
The fin shaft needs merely to be parallel to a radius of the roll axis, and perpendicular to a tangent of that radius, in an ideal world, on a boat with a perfect steel-set-in-rock roll axis.

I struggle to understand if and why you seem to be disagreeing with what I'm saying.
What is exactly the part of the second fin which I cut and pasted in the drawing below that doesn't meet all your requirements above?

Absolutely not. Straight fins on the keel would waste the maximum possible energy in sway+yaw. You might not feel that as the fins are only 6hp anyway and the boat will have some roll axis stiffness. Now, if you put curved fins onto the keel, they would produce the same force vector as a flat fin mounted on the deadrise at say 20degrees, so would intrinsically waste less energy in sway by having a higher vertical component of their force, resulting in a higher NmS of antiroll torque AOTBE. (Umm, the fact you even ask this question tells me you're not getting the vectors, MapisM...)

Ahem. Yet another case of not be getting the ball so going for the man?
Please, don't forget that the Garfield thing was very obviously a joke.
You might not have liked it, but it's hardly a justification for fighting back repeatedly, and also without joking at all.
Anyhow, if you seriously think that curved fins placed vertically along the keel would be better than straight fins in the same position, one of us must have lost the plot completely, I'm afraid.
And I'm genuinely interested to understand if I'm that one.
Now, can you explain me (in plain English, since I don't get vectors) if you would make such fins, with the shaft placed exactly vertical along the keel, curved to port or to stbd, and why?

You cannot seriously believe that a 50% increase in the NmS value wont result in an appreciable improvement in stabilisation, can you?

LOL, actually I never bought the 50% NmS increase, to start with...

 

[Tender_aft]

I'm not sure whether this is still a serious discussion or just a public cohone measuring exercise.

I lost interest in the physics a long time ago (as you seem to be trying to win points against each other on nuances). I am very interested in the subject though. Perhaps we should have a vote on whether this should be taken into private messaging, or done over a bottle of whisky and the last one standing wins the argument.

However, perhaps others are enjoying it (and maybe the arguments are still being thoroughly debated; I just stopped noticing). Vote anyone?

The two of you can always join together and pick on me after my inflammatory first sentence and then have some manhugs afterwards in the face of a new enemy.

 

[jfm]

I would give my fins a 99% score, not 95%, but 99% !

Bart, maybe a bit of a misunderstanding. I too would give them 99% or whatever, in that video and within their operating envelope. If another Canados 70 were anchored next to you with 1m2, it would have performed the same as your boat, 99%. BUT, your fins were at something like 75% of max in the video, and the 1.0 fins would be at 50%, or whatever the exact percentages are. As the waves/swell gets bigger, there comes a point where the 0.6 runs out of ability, but the 1.0 carries on. Now, each owner can select whether he wants stabilisation in bigger swells, or just modest swell like your video. That is personal choice. No-one is right or wrong on that.

But the point I was making when I linked to the BA FDC video was only a rebuttal of MapisM's spurious claim that CMC are proven right on their claims about fin size and I am proven wrong. CMC's claim, remember, was that electric is so good that you only need a 0.6 electric to get same result as a 1.0 hydraulic. The video proves that CMC claim was BS. The 0.6 fins were working hard in a moderate sea. A pair of 1.0 fins would not work anywhere near as hard as that - I've spent hours watching them. The video actually proves I was right, but no worries, it is just a mapism-JFM spat :-/

 

[jfm]

Hey MapisM, this time I am going to keep it really short, because we're pretty much done!

Oi, and you accused ME to not be getting the ball so going for the man?

Point of order matey. I never go for the man, with the exception of this thread. You went for the man, so you set the ground rules. I'm merely following them (in this thread only). "You've made your bed", if I may use an EN expression, and have lost the moral right to protest

at Mitsubishi there must be someone who understands all that MUCH better than both of us together, and multiplied by three for good measure.

. And what do you think he would say? Basically, Faraday, the Mitsubishi guy, all the physicists in the world, and moi, say 100% of the electrical energy consumed by the crane makes heat energy, and you say some of it makes kinetic energy. Go figure! (I'm not convinced the Mitsubishi guy knows that x3 better; but no matter)

Re. none of the FDC crew members having any other STAR experience, how can you say that - no matter how respectfully?

I think the statement is correct, but as ever, if anyone knows differently and corrects me I will eat my words, apologise and stand corrected

Exactly as it is in BA taken straight from the Sleipner testimonial video (video which could well be a great competitor in a "flattest anchorage ever" context):
If you look at the anchorage we're in now, it's kinda typical, in a photograph this would look very calm, but there is actually a gentle swell coming through the anchorage...

Tee hee! I'm smiling. "Photograph" means a still not video, btw! The guy on the video (!!) said that, because he couldn't see it and was hoping that for that that scene it would rough or a wake would come through or something to save the day, but it didn't happen. So yes I plead guilty to marketing BS about the sea state! Moving onto the facts, the 1.0 fins were almost asleep in that Sleipner video, working much <50% of their max, while the 0.6m fins were working their asses off in that FDC BA video, in a not-very-rough sea.

So far, that's your opinion. A respectable one, but still an opinion.
I'm afraid only independent tests carried out on AOTBE boats, one equipped with straight and the other one with curved fins could confirm/deny that.

It isn't merely an opinion, it is a claim based on vector analysis, CFD analysis of 3 real production boats (CFD is, I hope you understand, a seriously advanced science and not at all trivial or guesswork), plus actual results from the Princess 56. That's more than an opinion. These days, when guys design a plane and do all the maths on it, then build it, it flies first time. Just before it takes off for the first time, having done all that work, it isn't just someone's opinion that it will fly. It is a fact.

Anyhow, if you seriously think that curved fins placed vertically along the keel would be better than straight fins in the same position, one of us must have lost the plot completely, I'm afraid.
And I'm genuinely interested to understand if I'm that one.
Now, can you explain me (in plain English, since I don't get vectors) if you would make such fins, with the shaft placed exactly vertical along the keel, curved to port or to stbd, and why?

You would make one curved to port, and the other to starboard, but only so that asymmetry of the scoop/convex would be balanced out. If, magically, that asymmetry didn't exist, it would make no difference which way they curved. Incidentally, and it's a somewhat separate point, because the force vector of the curved fin isn't perpendicular to the stab shaft, they are better if they are out nearer the chines, unlike straight fins where the force vector stays the same at keel and chine. As you get near the keel with a curved fin you lose a decent chunk of the benefit of the changed force direction (you need to study the vector diagrams to see this). In fact, take that to its ultimate conclusion and take the curved fins PAST the keel right across to the opposite chine. In other words mount them in the normal position but with the curves going the wrong way. THEN they would be worse than flat fins because they would have a very short lever arm and the force vector would be more horizontal than the deadrise. (If you can see why that is true, you're understanding the vectors)

I struggle to understand if and why you seem to be disagreeing with what I'm saying.
What is exactly the part of the second fin which I cut and pasted in the drawing below that doesn't meet all your requirements above?

Look at my requirements again. The part it doesn't meet is the "on a boat with a perfect steel-set-in-rock roll axis". By the way, in that drawing you posted, both the fins function identically, so what I say refers to either/both of them, not just the second one.

Another shot at expl the vector thing: The force vector the fins create is in the direction of the blue angled arrow. Compare flat with curved - force vector of the curved fin is "steeper". Mathematically, this is the same thing as saying the vertical component of the curved fin's force vector is bigger, and the horizontal component smaller, than for the straight fin. THAT is the brilliance of this design. The boat has firm roll axis bearings in terms of vertical movement, but mushy bearings in terms of horizontal movement. If you had a 5 metre pole athwartships pole welded perpendicularly to the boats' roll axis, and sticking out of the hull midships, and if you were to apply 1000 newtons of force perpendicularly to the end of the pole for one second, you'd get more angular momentum in the hull (ie more anti roll effect) if the pole was horizontal coming out thru the master cabin window, than if it were vertical coming out thru the keel or the flybridge deck, because of the mushy bearing. (No-one has ever taken 2 identical boats and actually installed this pole vertically and horizontally, but I submit that the previous sentence is still a fact not an opinion, btw )

LOL, actually I never bought the 50% NmS increase, to start with...

Jeeze. What we have here is a bunch of engineers who have invested their own (not merely their shareholders') money making a product, commissioned heavy-duty CFD, installed them on a p56 and had them tested by Princess including David King at the helm, and filed the patent. And in any case, to any engineer or physicist, the thing self evidently makes a non trivial improvement just from looking at it, without the CFD. Then we have you, who doesn't understand the physics and force vectors at all, and even writes that the drag of a spoon pulled thru the water in "scoop mode" is the same as in "convex mode" (I had to do a double take at that, sheesh). Until this thread, you didn't even know that antiroll impulses to the boat's hull, expressed scientifically, are even expressed in NmS. And then you say that you don't buy the ~50% NmS results of CFD? I give up!

Anyway, happy to hear more thoughts if you wish but otherwise shall we pack it in and agree to disagree MapisM?

 

[jfm]

I lost interest in the physics a long time ago (as you seem to be trying to win points against each other on nuances).

Each to their own of course, but if you lost interest in the physics, this ain't the thread for you. The tech content of these posts (as distinct from the Garfield aspect!) is very much about the significant physics, and not the nuances. There are many nuances too, but we haven't and I hope wont discuss them

Stabilisers is a big and fascinating topic, both fins and gyros. The fluids of fins is very interesting, for a geek. For example, do you realise that in the last 1/3rd or so of the sweep of the fin in STAR mode, they are not stabilisers at all? They are the enemy - they assist the wave in rolling the boat. All stabilisers I mean, not just flat or curved ones. Curved ones, because they are more effective than flat fins AOTBE, for all the vector reasons given above, are worse than flat fins in this last 1/3rd of the stroke. I should post the CFD force versus time graphs for a typical fin, to illustrate this, if I can find one on the web. [/geekery]

 

[Deleted User YDKXO]

However, perhaps others are enjoying it (and maybe the arguments are still being thoroughly debated; I just stopped noticing). Vote anyone?

No, keep it going on the open forum. I'm enjoying this immensely, especially the physics. It's great to see 2 forum heavyweights slugging it out to a standstill

 

[benjenbav]

I finally whipped up the energy to tear the wrapper off my copy of MBY last night and read the article, which I thought was poor.

In precis: this is brilliant kit and the science is probably right. Wtf? It either is or it isn't.

At least on here there's been a proper discussion.

 

[oceanfroggie]

No, keep it going on the open forum. I'm enjoying this immensely, especially the physics. It's great to see 2 forum heavyweights slugging it out to a standstill

+1

Yes this whos got the biggest w***ie competition has been very entertaining and indeed very interesting to observe from the side lines.