Game changer from Seakeeper?

[Deleted User YDKXO]

Angular momentum seems to be the key figure in terms of performance, which suggests you'd need 3 x S5.
There's definitely no problem using two gyros though if packaging allows, a number of boats have done that.

My boat (65ft/44t) seems to fall somewhere between the S9 and S16 in Seakeepers stated weight/length terms so maybe 2 x S5 could be an option? For me the key point would be the ability to run 1 gyro using the existing inverter and batteries and only power up the gennie when I needed both gyros. Also I can see 2 x S5 gyros fitting into the aft lazarette of my F630 better than a single S16 and still leaving space for other stuff on top. Do these gyros get hot and do they need air space around them?

 

[Nick_H]

My boat (65ft/44t) seems to fall somewhere between the S9 and S16 in Seakeepers stated weight/length terms so maybe 2 x S5 could be an option? For me the key point would be the ability to run 1 gyro using the existing inverter and batteries and only power up the gennie when I needed both gyros. Also I can see 2 x S5 gyros fitting into the aft lazarette of my F630 better than a single S16 and still leaving space for other stuff on top. Do these gyros get hot and do they need air space around them?

They get hot, but not so hot you can't touch them, and they don't need airflow around them as they have a closed cooling circuit with raw water fed heat exchanger.

edit: I'm not so sure that two smaller units would package better though. If you look at the drawing the sphere drops below the housing, and normally sits in between the main stringers either side of the keel. Two smaller units side by side would sit much higher, though would be shorter so less likely to need bulkhead mods.

 

[kashurst]

Probably one for Nick_H
I've just been watching all the videso on Seakeepers website - they look pretty good. The one with the sunseeker 52 looks to be @ F4 - F5 blowing and it sits pretty still, not the sort of situation I would consider anchoring in or stopping for lunch etc. What are they like when pootling and planing in such a sea state?

 

[rubberduck]

We now need a fin system retro fit for smaller boats in the same price range, would be a winner I reckon.

 

[Deleted User YDKXO]

The anti roll torque isn't the main data (although, the S16 has >2x the torque of the s5). The real data item you should care about is the product of the torque and the time, ie the angular momentum. This is the size of the stabilisation impulse (so to speak) that the thing can exert before it hits the stops. This quality is stated by Seakeeper as the NMS figure. The 16 offers16k NMS while the S5 offers 5, so even THREE S5s give slightly less oomph than ONE s16

If due to the redundancy or space issues you do not want to fit one S16, then 3x S5s would be pretty much the same, though more expensive and heavier

But, in summary, when seeing what you're buying, the momentum (newtons x metres x seconds) is the figure you need to compare

Thanks jfm, understood. That's a shame. Certainly no point whatsoever in undersizing them to save a few bob

 

[vas]

We now need a fin system retro fit for smaller boats in the same price range, would be a winner I reckon.

+1

a 20K euro fin electric system capable of running on a 300Ah 24V system would be interesting.

need to read a bit more (and understand!) on this odd rotating tube system (only works while moving though...)

V.

 

[jfm]

We now need a fin system retro fit for smaller boats in the same price range, would be a winner I reckon.

That exists from both CMC and sleipner, and if space is tight the small sleipner rack and pinion actuator is remarkably good.

With all the discussion on fins ( which I'm guilty of ) let's not lose sight of nick's main point in the 1st post which is that this new small seakeeper is game changing in the 40-50 foot bracket. If you want fins then the small sleipner actuator plus vector fins is also game changing but maybe is 50 foot not 40 and I suspect more expensive in this size of boat. The future is bright!

Someone mentioned residuals above. To anyone buying a 45 to 55 today I'd say get the yielded to install these or at least prep the hull. You'll get your money back IMHO and meantime have a nicer ride. My first sq78 was hull 70 and fairlines first ever fins boat. They had done 2 gyro boats. I definitely got my money back as my boat was first pick on the used market. Fast forward 4 years and last weeks Southampton sq78 was hull 110. Of those 40 boats something like 25 to 30 have fins. 1 has gyros incidentally. That's how "must have" stabilisers are becoming. If stabilisers take over the 40-50 foot segment that fast you want to have them at resale time if you're buying now. All IMHO of course

 

[jfm]

+1

a 20K euro fin electric system capable of running on a 300Ah 24V system would be interesting.

need to read a bit more (and understand!) on this odd rotating tube system (only works while moving though...)

V.

Vas, IMHO a stab that doesn't work at zero speed is waste of money IMHO. The market wants zero speed, for all the reasons Nick mentions. Zeros are much cheaper if you consider the residual value effect IMHO and applying man logic of course

 

[Nick_H]

Probably one for Nick_H
I've just been watching all the videso on Seakeepers website - they look pretty good. The one with the sunseeker 52 looks to be @ F4 - F5 blowing and it sits pretty still, not the sort of situation I would consider anchoring in or stopping for lunch etc. What are they like when pootling and planing in such a sea state?

I haven't watched the vid, but generally I can say they're very effective for pootling in the kind of sea you'd normally get in a F4/5. Planing would be no problem at all, as the boats natural stability on the plane would leave less work for the gyro to do.

 

[vas]

Vas, IMHO a stab that doesn't work at zero speed is waste of money IMHO. The market wants zero speed, for all the reasons Nick mentions. Zeros are much cheaper if you consider the residual value effect IMHO and applying man logic of course

fully agree John,

just mentioned these tubes as I really don't remember how they work.

With my finances and boat I'd most likely spend 5K tomorrow if I could get a kit that I'll have to assemble and spend the next couple of years fine-tuning the sensors/reaction mechanism with a bit/a lot of programming. Not to mention that I'm sure there're a few others in this forum that would be interested and give a hand in programming Hell, I've done that tuning the ECU of my Fiat coupe and I still enjoy it immensely 8yrs down the road...

however, I wouldn't justify 20K anytime and wouldn't be able to fit the small seakeeper in my lazarette or e/r anyhow without completely blocking access from lazarette to e/r.

Wonder what's the actual cost of the el/motors assembly for a small set of fins (half the size of Bart's ones let's say) but that's all highly HYPOTHETICAL!

cheers

V.

 

[JumbleDuck]

Am I right in guessing that this is more than just a big gyroscope bolted to the hull - that there is a system (hydraulic) which forces precession in order to get a stabilising moment? And does it counter rolling torque by producing pitching torque, yawing torque or a bit of both? I'm interested because I have been doing a bit of reading up about this for work recently ...

which was an interesting idea but did some unpleasant things if either wheel went down a pothole.

 

[Nick_H]

Thanks jfm, understood. That's a shame. Certainly no point whatsoever in undersizing them to save a few bob

I agree entirely, but i'm not sure a 9000 or 2 x 5000 is undersizing. Princess achieved good results with a 7000 on a P62, and I know the 8000 works well on a Sq 65, so 9-10,000 NMS may well be sufficient to achieve good results on your boat. It's also not just about length and weight, the metacentric height is also very relevant. Seakeeper used to demand this info from any prospective customers, but I think they realised it was putting people off as no-one knew where to get that data, but on a borderline application it may be worth finding it out and discussing with their technical people.

On the point about not running the genny underway, I worked out my genny costs about £1.50 an hour to run, you need it anyway if you're cooking or running the aircon, you can't hear it over the engines even at tickover, and even at pootling speed the time spent underway is dwarfed by the time at anchor. I was considering getting an inverter, but the payback for the unit and installation is probably 10 years.

 

[jfm]

Am I right in guessing that this is more than just a big gyroscope bolted to the hull - that there is a system (hydraulic) which forces precession in order to get a stabilising moment? And does it counter rolling torque by producing pitching torque, yawing torque or a bit of both? I'm interested because I have been doing a bit of reading up about this for

A boat gyro counters rolling purely by creating rolling torque. Not pitching or yawing. The precession axis is athwart ships and horizontal while the gyro's spin axis is vertical, so this must be so

The precession isn't induced. It is in big ship gyros but not these ones. The precession is however damped ie slowed down by hydraulic cylinder. In sea keeper it is "actively damped" with acceleration sensors and computer and algorithms to control the speed of the hydraulic cylinder. But it is still not induced. In Mitsubishi it is just damped with no computer control of the damping rate. That is mainly why sea keeper is the better leisure boat gyro

 

[MapisM]

He said the gyro merely has to spin at 1000rpm and that alone creates the antiroll torque.

ROTFL, I hope that at least the number is your typo and he actually said 10k, because otherwise he should also think that the two big flywheels in the e/r of his SL104 should be more than enough (I'm safely assuming that he wouldn't even think about the different rotation axis) to stabilize the boat, without needing anything else...!

On a more serious note, actually I'm not so surprised: while the way fins work is very intuitive, exactly the opposite is true for gyros.
I mean, that guy might well be an excellent captain, with a great hands-on experience on anything that really matters onboard, without understanding a iota of gyroscopic precession etc.
Of course, this is no excuse for pretending to know better than yourself, when he was obviously aware that he was either a) making his objections up, there and then, or b) reporting something he surely didn't hear from a real expert.
Either ways, a clear cut case where silence would have been his best answer...

But apropos of engineering knowledge (lack of, that is) of some professionals, I had a similar experience a quarter of a century ago, no less.
Which btw explains nicely why I'm not surprised by what you experienced.
I was attending with swmbo a boat license course (as you might remember, in IT a license is mandatory for anything but very small boats).
The teacher was a former tankers and container ships captain, who eventually had enough of being anywhere but at home for most of his life, and established a school in Lake Como. A very nice chap, who began his career in the Navy, and made also some offshore racing experiences along the way.
In other words, someone I would trust as a skipper for going anywhere with any sort of vessel, as long as he thinks it's good enough for the job.

But while explaining the compass, he mentioned that with magnetic compass we had to consider the difference between the magnetic and the true N. And he also added that this does not apply to the gyrocompass, which is used on ships, but that is very expensive and only necessary in steel vessels, hence not used in pleasure boats.
Now, back in those days, rather diligent as I was, I had studied the subject before attending the lesson, so I knew perfectly that the differences between the two systems were way larger than just cost.
So, the debate which followed went on along these lines:
MM: I understand that the gyrocompass doesn't rely on magnetism, but how does it find out where the N is?
T: Well, it relies on a gyroscope. It's a sort of dish, spinning very fast. Just think of a spinning top, which always tends to stay horizontal, hence "finding" the tangent to the curved earth surface.
MM: Ok, but what use is a tangent plane alone, when what we actually need is the N-S vector?
T: Ermm, actually I'm not aware of all the technicalities behind a gyrocompass, which is an extremely sophisticated thing. But there must be some subtle differences which it's capable to capture somehow....
Bottom line, not much different from your SL captain, aside from being more honest!

Re. your video, yup, I already saw it. Very nice, but I suppose it could have been even more effective by switching the stabs on and off.
Not that I'm wishing you an F8 sea for your next cruise of course, but you might keep your camera charged, just in case....

 

[MapisM]

need to read a bit more (and understand!) on this odd rotating tube system (only works while moving though...)

I think you are talking of the stabs based on the Magnus effect - more in this website, just as an example:
http://www.dmsholland.com/wp-content/uploads/2013/05/Brochure-RotorSwing_ENG.pdf
I understand that they can actually work also at zero speed, by "paddling" the cylinder back and forth, on top of the normal rotation.
Apparently, this can create enough of the water flow which is necessary to get the stabilizing effect (still by rotating the cylinder, anyway).

But please, don't post a thread with a successful DIY design, construction and installation of such system on Mythos.
What you have done with the rebuild is already more than enough to leave most of us (myself for sure, anyway) speechless upon each and every update of yours...!

 

[JumbleDuck]

A boat gyro counters rolling purely by creating rolling torque. Not pitching or yawing. The precession axis is athwart ships and horizontal while the gyro's spin axis is vertical, so this must be so

If the gyro has a vertical (yaw) axis and you force it to precess round a horizontal athwartships (pitch) axis then you must get a moment round the third (horizontal, longitudinal, roll) axis. The cost of getting that rolling moment is the pitching moment you had to apply to get precession. Or, to put it another way, if you have a vertical axis gyro and you try to roll the axis, it will resist that by producing a pitching moment. I really don't see how you can get a gyroscope to produce a rolling moment only.

I could be wrong, though, as it's a while since I taught 3D kinematics and it's late at night, so I'd welcome correction.

Edit: looking at the diagrams it seems to me that those hydraulic dampers are there to control the pitching moment produced when roll is being resisted.

 

[MapisM]

Despite Seakeeper stating that running load of the 8000 series is 1.5-2 kw, mine draws nothing like 8 amps after the initial spool up, in fact most of the time it barely registers on the ammeter. Even if it was 1.5-2kw then that's still only 80A at 24V, so do-able with inverter and alternators.

Apropos of electricity requirements, just for the records, I heard recently from BartW a very interesting thing:
After upgrading BA inverters, he's now able to run the electric fins stabs at anchor for A FEW HOURS (I'm quoting from an email exchange we had), without turning the genset on. Which is something I found absolutely amazing.

Just to put this in perspective, hydraulic fin stabs, at anchor, require:
1) the genset running;
2) a VFD device to get three-phase current;
3) a 3-ph electric motor spinning a powerful hydraulic pump;
4) a high pressure compensation tank.

Under way, IIRC he has always been able to do that, even with the previous smaller inverters.

Not sure if he will see this thread, but if he does maybe he can tell us more about his latest experiences....

 

[grumpy_o_g]

A boat gyro counters rolling purely by creating rolling torque. Not pitching or yawing. The precession axis is athwart ships and horizontal while the gyro's spin axis is vertical, so this must be so

The precession isn't induced. It is in big ship gyros but not these ones. The precession is however damped ie slowed down by hydraulic cylinder. In sea keeper it is "actively damped" with acceleration sensors and computer and algorithms to control the speed of the hydraulic cylinder. But it is still not induced. In Mitsubishi it is just damped with no computer control of the damping rate. That is mainly why sea keeper is the better leisure boat gyro

Sorry jfm, trying to get my head round this (not that I'll ever need to know it). I'd always assumed that the gyro had torque applied to try and rotate it and the fore and aft axis to induce an anti-roll torque. Are you saying that the boat's roll induces precession on the gyro which then tries to force the bow or stern down but can't because of the buoyancy? Presumably the damping is then to make sure that the gyro smoothly dampens the roll rather than creating an unpleasant or uneven motion by upsetting the boats natural roll frequency?

 

[JumbleDuck]

Apropos of electricity requirements, just for the records, I heard recently from BartW a very interesting thing:
After upgrading BA inverters, he's now able to run the electric fins stabs at anchor for A FEW HOURS (I'm quoting from an email exchange we had), without turning the genset on.

Another question from an interested raggie ... I though stabilising fins were hydrofoils and rotated to generate lift (up or down) in order to keep the boat level-ish. How doe they work when the boat is stationary? Does it depend on having some tidal flow?

 

[jrudge]

Just bear in mind that the cost of fitting is about the same price as buying the thing. I have a quote for usd68000 plus vat and delivery for the unit, but fitted it is some 75000 plus vat as half the boat has to come to bits.