Boat in build pics (2013 Fairline Squadron 78)

[Lozzer]

Recently had Princess factory on board boat and talking to them about the stabiliser system . Apparently this stuff is under huge pressure and high temperatures especially when called into action.

Princess recommend that in the event of the raw water cooling failing you should disengage the PTO and put in blanking plates provided. It's about a 20 minute job allegedly. . Failure to do so could have significant consequences.

Enough info to persuade me to go through the procedure with them.

JFM. have to agree with you about view from trains and boats. Give me a boat any day of year.. I would say that princess and ferretti to name but a few are offering a different style window with fewer supports.

Your boats coming along nicely though looking forward to hearing what nav system your going to go for.

 

[jfm]

Recently had Princess factory on board boat and talking to them about the stabiliser system . Apparently this stuff is under huge pressure and high temperatures especially when called into action.

Princess recommend that in the event of the raw water cooling failing you should disengage the PTO and put in blanking plates provided. It's about a 20 minute job allegedly. . Failure to do so could have significant consequences.

Enough info to persuade me to go through the procedure with them.

JFM. have to agree with you about view from trains and boats. Give me a boat any day of year.. I would say that princess and ferretti to name but a few are offering a different style window with fewer supports.

Your boats coming along nicely though looking forward to hearing what nav system your going to go for.

Hi Lozzer
Pressures are in the order of 200bar. That is huge compared to most things, but run-of-the-mill in the world of hydrualics.

That's interesting to hear about undoing the PTO. Thing is, there are 2, (unless you have only one engine with a PTO on the Prin?) and you'd have to disengage both, otherwise there is no point. I find the comment a bit implausible but I'll look into it. If you lost the seawater cooling (Sleipner has digi read out on both helms; does ABT Trac?) there would be an alarm and the stabs might shut down automatically (I'm not sure if that has been coded in...) but if they didn't you'd turn them off. At this point there is no power being absorbed by the system other than pumping friction, and the PTOs are taking a fraction of a HP from the engines, not the 30hp or so they can take when work is being done. So I doubt the heat generated is large. But that's intuitive, coupled with the thought that the "engineer" from Princess might not actually have been an engineer as often happens with the word "engineer". I'll see if I can get some more data on this however - thanks for the ideas

Princess's new mullionless hull windows are lovely things. The view out is simply stunning. I've been on at Fairline about these but there is a lot of engineering to be done so it wont be a quick thing, and likely wasn't for Princess. Top job by Princess though - I think they are first in the world with such big windows

 

[scubaman]

The stairs will look lovely and I agree with your mods on the steps pictured 100%.

But, and I realize that I'm heavily in the nitpicking territory here, the way the handrail is fixed to the fly is not on par with rest of the details. It looks a bit clunky and has a slightly self made feel to it, IMHO.

From the drawings I gathered that it's going to be similar in your steps.

I don't have any suggestions on an alternative way of doing it, though...

Edit: would it be possible to leave out the vertical part of the L-plate and fix it from the horizontal part only. There shouldn't be too much downward forces in play for it to be a problem? Or maybe there would be...

 

[Elessar]

Hi MapisM
I did think hard about using the same zig zag stairs outside as inside but ultimately I prefered the straight spine look outside. It is more minimal. Also, the inside stiars are intrinsically less stiff which is ok inside because you sort of move down them more slowly plus the height span is about 6 or 7 steps compared with 2 or 3 more outside

As mentioned above there is one other s78 (now in USA W Coast) built with this type of stair, last year. Pics below. I think this was a fine job but the owners made different choices from me: they used square not rectangular section; about 80 not 90 deg joint twixt main spine and short cantilevers which has its pros and cons; straight spine with same bottom landing point as normal stairs therefore too steep for me (I have walked up and down them) but their owners chose this because they wanted the furniture rack underneath (pics2+3 below) which i would never have; handrail should be round not rectangle section imho; handrail lands on bottom step too far aft imho; no downlighting. In the 3rd pic below, the 2nd step from top, ie the one above the fire extinguisher, will be around 200mm further forward on my boat hence making them significantly less steep (bottom of stairs is in same position)

But moving away from the details the first pic below shows the general look that mine will have, which I like. It will also look good at night with LED down lighting (I'm using the Osram LED fittings made in Denmark by Cabin that shoot 4 pencil streaks of light downwards; same as interior stairs). 4th pic below is mine, for easy comparison

Happy to disagree on hull windows . I like them. Much we prefer trains to boats, fact is trains have better viewing windows than boats (if only the view were as nice as the sea...). BTW it is not expensive in mould tooling to change windows - they are just blocks on the inside of the main mould and can be changed any time for € peanuts

And happy to disagree a bit on stabiliser NKOTB stuff. To be fair most of the components are catalogue items made by the big manufacturers (hydraulics by Rexroth; bearings by SKF, hoses in my case by Phoenix; and so on) hence the absence of years and years of testing isn't the issue you say, imho. The floating centreline is however an improvement worth calling home about, at least on a P boat - the fuel/range benefits are definitely worth having

don't like the way the joints in the teak stop just to port of the stairs on that one........

 

[jfm]

The stairs will look lovely and I agree with your mods on the steps pictured 100%.

But, and I realize that I'm heavily in the nitpicking territory here, the way the handrail is fixed to the fly is not on par with rest of the details. It looks a bit clunky and has a slightly self made feel to it, IMHO.

From the drawings I gathered that it's going to be similar in your steps.

I don't have any suggestions on an alternative way of doing it, though...

Edit: would it be possible to leave out the vertical part of the L-plate and fix it from the horizontal part only. There shouldn't be too much downward forces in play for it to be a problem? Or maybe there would be...

Hi Scubaman. I get your point. On those photos the geometry of the stairs and the rail is quite different from mine. The L-Plate is much further aft than normal, and therefore more obvious/eye catching. I will have the L-plate but it will land in a less prominent position - about 125mm in front of the lightswitch recess. I know it's hard to believe from that pic: I'll post another pic after it is all built

 

[MapisM]

Happy to disagree on hull windows . I like them. Much we prefer trains to boats, fact is trains have better viewing windows than boats (if only the view were as nice as the sea...). BTW it is not expensive in mould tooling to change windows - they are just blocks on the inside of the main mould and can be changed any time for € peanuts

...............

Princess's new mullionless hull windows are lovely things. The view out is simply stunning. I've been on at Fairline about these but there is a lot of engineering to be done so it wont be a quick thing, and likely wasn't for Princess.

Well, it looks like we don't actually disagree, eventually - neither on the possibility to do something better, nor on the higher commitment (=cost) required.

On the matter of floating centerline, did Sleipner make any "scientific" measurement of the consumption difference with/without it?
After all, it should be just a matter of turning the feature on/off via software, and see what happens on the Cat displays.
Intuitively, it's extremely hard to believe that the difference can be meaningful, even on P boats.
I mean, of course the fins drag take a significant toll on consumption/range at P speed, but sorry, I don't buy the idea that the centerline thing alone can really reduce that in any measurable amount.
I'm assuming that we're talking of keeping the system active while cruising, of course - which means that the fins are constantly moving anyway.
With sea conditions that don't require the stabs, even my archaic Naiad have the simplest and most effective floating centerline known to mankind: with the system off (completely off, NOT center-locked), the fins move freely and are therefore, by definition, always self-centered along the hydrodinamic flow...

 

[Lozzer]

Hi Lozzer
Pressures are in the order of 200bar. That is huge compared to most things, but run-of-the-mill in the world of hydrualics.

That's interesting to hear about undoing the PTO. Thing is, there are 2, (unless you have only one engine with a PTO on the Prin?) and you'd have to disengage both, otherwise there is no point. I find the comment a bit implausible but I'll look into it. If you lost the seawater cooling (Sleipner has digi read out on both helms; does ABT Trac?) there would be an alarm and the stabs might shut down automatically (I'm not sure if that has been coded in...) but if they didn't you'd turn them off. At this point there is no power being absorbed by the system other than pumping friction, and the PTOs are taking a fraction of a HP from the engines, not the 30hp or so they can take when work is being done. So I doubt the heat generated is large. But that's intuitive, coupled with the thought that the "engineer" from Princess might not actually have been an engineer as often happens with the word "engineer". I'll see if I can get some more data on this however - thanks for the ideas

Princess's new mullionless hull windows are lovely things. The view out is simply stunning. I've been on at Fairline about these but there is a lot of engineering to be done so it wont be a quick thing, and likely wasn't for Princess. Top job by Princess though - I think they are first in the world with such big windows

Hi John

I have PTO on both engines, I believe I can isolate engines individually but in doing so you must remove and blank off. Like you I can bypass bow or stern thruster if necessary.

I only have one readout which is in the wheelhouse, I would like one on the fly but they are very sensitive to sunlight. Had to replace one already. Yes they alarm and I hate hearing it often have to clear strainer which is a pain, especially when underway.

I will check the manual on cooling issues tomorrow and advise.

The engineer was an engineer. Well he replaced engine mounts plus helped me with other jobs. I have known him for a number of years as senior techie in after sales. What he doesnt know about Princess is probably not worth knowing.

Regards

Lozzer

 

[MapisM]

I'm also curious to hear more about the reasons for disengaging the PTOs when cooling fails, also because I wouldn't want to be spending those 20 mins (x2 ?) in the e/r, possibly offshore, in some rough stuff and with no stabs...
I've been in such situation once, and had to cruise for another couple of hours (with the stabs off, of course) before I could sort it out, but the oil temp always stayed well below the normal operating temperature.
Otoh, my pump is belt driven. One thing I can think of with PTOs is that the oil temperature could build up due to heat transfer from the engine block to the pump, but what do I know...?
Btw, in ABT stabs the center lock is mechanic, which means that also with the hydraulic system turned off you could still reverse without affecting the boat maneuverability (jfm/Sleipner, take note... )

 

[STEVEDUNSTABLE]

hi jfm..... just thought i,d ask about your fuel tank under the master berth.!!!....is the tank fitted with baffles in side or is it fitted inside a sound proof casing??? i would be very upset to hear that you were getting woken during your much needed down time by lots of "at anchor splippin n sploppin"!!!!

 

[jfm]

Btw, in ABT stabs the center lock is mechanic, which means that also with the hydraulic system turned off you could still reverse without affecting the boat maneuverability (jfm/Sleipner, take note... )

You have that entirely the wrong way round. With sleipner and a total hydraulic failure* you can shut the hyd valves manually and the fins are locked, hence you can reverse the yacht. With ABT you cannot move the locking pin cos it needs working hydraulics which you don't have, so you cannot lock the fins. Sleipner is therefore more fail safe.

*except of course if the failure involves a loss of the oil. In which case neither sleipner nor ABT nor any other stabs will lock, so you'd just jury-rig. Eg lock them with spanners and wedges on the actuator while you reversed into your berth for repairs

 

[Elessar]

You have that entirely the wrong way round. With sleipner and a total hydraulic failure* you can shut the hyd valves manually and the fins are locked, hence you can reverse the yacht. With ABT you cannot move the locking pin cos it needs working hydraulics which you don't have, so you cannot lock the fins. Sleipner is therefore more fail safe.

*except of course if the failure involves a loss of the oil. In which case neither sleipner nor ABT nor any other stabs will lock, so you'd just jury-rig. Eg lock them with spanners and wedges on the actuator while you reversed into your berth for repairs

Locking pins on Trac are held locked by a spring and unlocked by hydraulics so they do fail safe in case of oil loss. Assuming auto lock specced.

 

[jfm]

hi jfm..... just thought i,d ask about your fuel tank under the master berth.!!!....is the tank fitted with baffles in side or is it fitted inside a sound proof casing??? i would be very upset to hear that you were getting woken during your much needed down time by lots of "at anchor splippin n sploppin"!!!!

Quite a few people have asked me that Steve. No, it's silent. Reason is easy: it is nearly always full because my default valve setting is for it to be gravity fed by the two main tanks (they're higher). I have to be down to less than 1/4 on the fuel gauge before there is air in that tank. The odd time I have been at anchor that low on fuel, maybe 2-3 nights in 1.5 years on Match1, I still never heard it sloshing. There are baffles, plus the sound has to get through a plywood bed carcass and a mattress. You would never have known there was a fuel tank there on Match1 (by noise or smell) if you didn't know. That's why I'm re-ordering the same design on Match 2. About 5 other Sq78s since Match1 also ordered this tank and there are no complaints

To be honest the boat doesn't move that much or that fast on anchor because she is a rather fat lady - 60tonnes and 18foot wide. If she moves much you need to be in a different anchorage anyway

 

[jfm]

Locking pins on Trac are held locked by a spring and unlocked by hydraulics so they do fail safe in case of oil loss. Assuming auto lock specced.

Ah ok, fair enough, thanks for correction - my comments on that point were wrong, sorry

You can comment on Trac's reliability though. Correct me on the exact numbers but you've been on a new ABT-stabbed boat as skipper about 30 days and for 20 of those theTracs failed or worked only partially due to tech failures, right? That compares with my 100 or so Sleipner days with zero failures. And Steve Dashew with his zillions of miles doesn't sound like he's a Naiad fan - he says here
"Steve Dashew Reply:
May 16th, 2011 at 3:37 pm
NAIAD now confirms that the fin was defective and should not have sheared off at the insert."
The NKOTB are doing a reasonable job of it

 

[jfm]

Hi John

I have PTO on both engines, I believe I can isolate engines individually but in doing so you must remove and blank off. Like you I can bypass bow or stern thruster if necessary.

I only have one readout which is in the wheelhouse, I would like one on the fly but they are very sensitive to sunlight. Had to replace one already. Yes they alarm and I hate hearing it often have to clear strainer which is a pain, especially when underway.

I will check the manual on cooling issues tomorrow and advise.

The engineer was an engineer. Well he replaced engine mounts plus helped me with other jobs. I have known him for a number of years as senior techie in after sales. What he doesnt know about Princess is probably not worth knowing.

Regards

Lozzer

Hiya. Still sounds to me like you'd need to remove and isolate both PTOs then, if the cooling failed.
I'm sure the guy was knowledgeable but he is sounding like a tech not an engineer, from your post. My concern is that he might have missed the point (when he told you to remove the PTOs on a cooling system failure) that once you turn the fins off by shutting the valves there is much less heat being generated in the hydraulic oil anymore, even if the PTOs are still spinning. That's how it feels intuitively and engineeringly, though I'm happy to be corrected if there is another engineeringly sound explanation of the thermodynamics

 

[jfm]

On the matter of floating centerline, did Sleipner make any "scientific" measurement of the consumption difference with/without it?
After all, it should be just a matter of turning the feature on/off via software, and see what happens on the Cat displays.
Intuitively, it's extremely hard to believe that the difference can be meaningful, even on P boats.
I mean, of course the fins drag take a significant toll on consumption/range at P speed, but sorry, I don't buy the idea that the centerline thing alone can really reduce that in any measurable amount.
I'm assuming that we're talking of keeping the system active while cruising, of course - which means that the fins are constantly moving anyway.
With sea conditions that don't require the stabs, even my archaic Naiad have the simplest and most effective floating centerline known to mankind: with the system off (completely off, NOT center-locked), the fins move freely and are therefore, by definition, always self-centered along the hydrodinamic flow...

Oh yes, we activated/unactivated the function and got an instant better reading off the Cat/Garmin displays. If you set the fins correctly centred at 28kts, then drop to 20ts, measure fuel burn, then recentre them correctly for 20kts, you see instant meaningful fuel improvement, in the order of 1 litre per mile. I've seen it with my own eyes and also I don't get your "intuitively it's hard to believe" thing; on the contrary I'd say intuitively you'd expect to get a meaningful and measurable difference. You should get your intuitively gauge recalibrated - we're talking about dragging 2 x 1msq fins with 70mm shafts at 20-25kts, sheesh

Your reference to letting them free float misses the point a bit. All fins have a centre when they're operating, and the "correctness" of that centre moves with speed, and it's that which needs to be correct for best fuel burn esp in a P boat. I do agree the effect is greater when the fins are moving modestly as opposed to in a very rough sea, but it's still meaningful. BTW sleipner also will flap freely, if you want, but you never would want with dynamic centring

 

[MapisM]

Your reference to letting them free float misses the point a bit. All fins have a centre when they're operating, and the "correctness" of that centre moves with speed, and it's that which needs to be correct for best fuel burn esp in a P boat. I do agree the effect is greater when the fins are moving modestly as opposed to in a very rough sea, but it's still meaningful.

I understand that perfectly, but that's exactly where my "intuitively gauge" leads me to opposite conclusions.
While the stabs are working, it's only incidental that the fins pass in the hydrodinamic centre. And even when they do, it might well be that in such position they are inducing more drag anyway, because they are working to contrast the boat roll - which is inherently much stronger than the effect of speed on the water flow.
I would even think that while the stabs are working, the concept of a centerline becomes meaningless as a whole. Each fins position is bound to be roll-driven rather than speed-driven at any given moment, otherwise what would be the point of stabs?!?
Otoh, I fully agree that if you would cruise at speed with the fins exactly center-locked, the drag would be higher than with fins automatically pointing slightly inward while the speed increases - and in this sense, the mechanical center lock could be criticised.
Then again, as I said, if and when the stabs are unnecessary, the obvious choice is to leave them turned off, which allows the fins to always self-position according to the water flow.
And btw, the centre "correctness" of freely moving fins is even better than with an hydraulically forced (albeit dinamic) position, whenever not only speed but also current gets in the equation.
Glad to stand corrected if I'm missing something, but I'm afraid that the principle of water being splashed sideways by the hull, in itself, doesn't hold water at all... so to speak!

PS: I assume that the test you mentioned was made with the fins centered - i.e. comparing the results between the fins steadily parallel and the fins steadily pointing inward according to speed. A 1 litre per mile improvement with the stabs working normally is something I would hardly believe if I saw it with my own eyes....

 

[Elessar]

Ah ok, fair enough, thanks for correction - my comments on that point were wrong, sorry

You can comment on Trac's reliability though. Correct me on the exact numbers but you've been on a new ABT-stabbed boat as skipper about 30 days and for 20 of those theTracs failed or worked only partially due to tech failures, right? That compares with my 100 or so Sleipner days with zero failures. And Steve Dashew with his zillions of miles doesn't sound like he's a Naiad fan - he says here
"Steve Dashew Reply:
May 16th, 2011 at 3:37 pm
NAIAD now confirms that the fin was defective and should not have sheared off at the insert."
The NKOTB are doing a reasonable job of it

Yes you know the tale. I had one fail in the dark, in very high winds, just I was going off the continental shelf ie going from 200m of water to 4000m and the sea was most unsettled. The fin was pinned to one end stop so I couldn't get the locking pin in, and there were warnings in the manual about possible hull fracture if you didn't.
The manual itself had a nice flow chart which I traced to "call factory". Useful.
I thought I must have had rope or debris pinning it to one end, so we zig zagged to move the fin and eventually got it locked. We did in the process get hit by a huge wave beam on which of course we couldn't see coming, which was interesting, and we rather shuffled most of the contents of the boat in the process.
It was actually a hydraulic problem and if I had turned an engine off the fin would have centred. I didn't find that out till we got to port 5 days later, even though the weather calmed after 3 and I tried again to fix it.
Fixed it in Gibraltar and in failed again less than 24 hours later. Fixed properly when bits arrived to Malta and I fitted them. I still smell of the oil.

 

[mjf]

Yep - once again a quite excellent thread and most interesting to watch her grow....

This white stuff in the teak - what's the fuss about ? I have this in my shower and Teak and Holly on the galley sole.

 

[jfm]

I understand that perfectly, but that's exactly where my "intuitively gauge" leads me to opposite conclusions.
While the stabs are working, it's only incidental that the fins pass in the hydrodinamic centre. And even when they do, it might well be that in such position they are inducing more drag anyway, because they are working to contrast the boat roll - which is inherently much stronger than the effect of speed on the water flow.
I would even think that while the stabs are working, the concept of a centerline becomes meaningless as a whole. Each fins position is bound to be roll-driven rather than speed-driven at any given moment, otherwise what would be the point of stabs?!?
Otoh, I fully agree that if you would cruise at speed with the fins exactly center-locked, the drag would be higher than with fins automatically pointing slightly inward while the speed increases - and in this sense, the mechanical center lock could be criticised.
Then again, as I said, if and when the stabs are unnecessary, the obvious choice is to leave them turned off, which allows the fins to always self-position according to the water flow.

MapisM I think we are agreeing on the basic principles - would be so much easier over a beer, LOL!

Yes when the stabs are working hard, the centreline is irrelevant. I said that, perhaps not clearly sorry, but 100% agreed.

But where we differ is in good weather/almost flat seas. Sure, in perfectly flat sea you can turn the stabs off and let them free float = minimum drag. But that hardly ever happens. What happens most of the time in the Med is you have almost calm weather, when the fins do very little, but still do something, and of course you get the odd patch of waves and you pass a boat's wake now and again when the stabs properly "wake up" for a little while and keep your boat flat. All this is maybe 3/4 of med cruising, and in this mode having the correct centre does save you meaningful fuel (at least in a P boat at say 15 litres/mile and a weekend is several €thousand in fuel)

And btw, the centre "correctness" of freely moving fins is even better than with an hydraulically forced (albeit dinamic) position, whenever not only speed but also current gets in the equation.

Yes, the freely moving self-taught centre is always more perfect, but you only have that if the fins are off, which as explained above is hardly ever what you want to do. Sleipner's computer-remembered dynamic centre is the next best thing, and the naiad/ABT fixed centre is at the end of the line in terms of attractiveness. Current is a total irrelevance (those Aus wines must be good MapisM mate ); current is merely movement of water relative to the land, and all boats/stablisers cannot see currrent when out at sea (as you well know!).

PS: I assume that the test you mentioned was made with the fins centered - i.e. comparing the results between the fins steadily parallel and the fins steadily pointing inward according to speed. A 1 litre per mile improvement with the stabs working normally is something I would hardly believe if I saw it with my own eyes....

No, that assumption isn't correct. Give me some credit that I wouldn't deliberately do a flawed experiment! The tests were done as follows (before dynamic centre software was installed):
(a) set boat say 28kts in flat sea, straight line
(b) via set up touch screen, let fins float freely. See from the fin position indicators that they have settled steady
(c) then store the position of the fins as the "centre" in the computer's memory
(d) Now drop to 20kts. Measure fuel rate over a minute to get a steady/average reading for "running at 20kts with a 28kt centre position"
(e) Now re-set the centre as per (b)+(c)
(f) Measure again the fuel burn (now "running at 20kts with a 20kt centre position") and compare with (d). =Measurable clear improvement in the order of 1 litre per mile

 

[MapisM]

MapisM I think we are agreeing on the basic principles - would be so much easier over a beer, LOL!

Yeah, no doubt about that!
Why don't you jump on a plane before the year end and join us for an anticipated (+11 UTC!) new year's eve, looking at the fireworks above the Opera House?
Maybe with some bubbly stuff, rather than beer...
...though I must say that talking of AU wines, the good ones are mostly red.
I also found some decent Sauvignon actually, but sparkling wines are a tad disappointing.
Even the few ones which are labeled as Méthode Champenois could barely compete with a French or Italian Charmat - for my tastes, anyway.

Re. the technical debate on the centerline, we're getting there I think.
Your last explanation of the test you made is in fact almost exactly what I envisaged.
In hindsight, I realise that I'm the one who wasn't clear enough, when I said "comparing the results between the fins steadily parallel and the fins steadily pointing inward according to speed", because with the floating centerline, obviously the fins are not perfectly parallel also at 20kts, so I should have said "comparing the results between the fins optimally centered for X kts but cruising at Y kts, and the fins optimally centered for the actual speed" - or something along these lines.
Anyway, the keypoint still is that your tests were made in flat sea, which means that the results applies to conditions when the fins are steadily centered most of the time (even if the stabs are on, and not center-locked).
Obviously, that's not what I had in mind when I said that I couldn't believe the 1 litre per mile improvement "with the stabs working normally".
In those conditions, my (personal) choice would be to leave the system off, thus killing two birds with one stone: fins freely floating, hence always optimally self-centered (though that's not so relevant at the speeds of my trawler), and (most important) pump not absorbing any power.
So, at the end of the day, my very old stabs system and the much more sophisticated Sleipner algorythms/controllers would achieve the very same final result.

Your point on the "real world" cruising conditions in the Med is intriguing, though.
First of all, I agree that if you wish to leave the system on also in totally flat conditions, just in case you pass the odd boat wake, the dynamic centerline can make sense.
My solution to this problem is a) cruising in uncrowded areas, and b) shout to the crew when crossing the odd boat's wake.
But I'll concede that this ain't a hi-tech answer...
Secondly, I also agree that most of Med pleasure boating is done in almost calm sea, where the majority of boaters is happy to cruise without even knowing that stabs exist, but anyone with a stabbed boat would never leave them off, because they know that they do make a difference, also in those conditions.
What I'm not convinced of is that the centerline thing can still be somewhat relevant, as soon as the fins are actually working, no matter how slowly.
I mean, in my experience, there are three variables which are visibly (just looking at the gauges) very different, depending on the sea conditions:
1) speed of fins movement;
2) angle of rotation;
3) length of oscillation periods.
Now, in the almost flat conditions we're talking about, ALL of them are lower than in rough sea. But even if the fins motion is much more gentle, it's very rare to see them steadily centered for any meaningful period of time.
That's why I'm skeptic on the relevance of the dynamic centerline in any conditions where it's worth keeping the stabs turned on.

Re. current, your objection makes me think that you must be in SoF, where wines are even better than in AU...
Scenario: cruising from A to B, true route 90°, stored on the plotter, a/p on track mode.
Question: does the optimal fins centerline remains the same with a) no current; b) current flowing E or W; c) current flowing N or S?

On a separate note, now I remember that Elessar already mentioned his troubles with ABT. And yes, I know the story of Naiad on Windhorse.
But!
Your 100 days of zero failures also compare with a total of 17 years on my boat...
Besides, Dashew didn't choose the NKOTB when he built his ocean crossing vessel, to start with.
And God only knows what other problems he might have had with them.
In fact, if you think about it, it's not surprising that there aren't many reports on Sleipner troubles, compared to Naiad and also ABT. Assuming 100 as the total number of stab equipments cruising around the world, at a guess Sleipner is still far from appearing in the second decimal place...