Game changer from Seakeeper?

Nick_H

Nick_H

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www.ybw-boatsforsale.com
Seakeeper have announced a new gyro stabiliser for boats up to 20 tonnes ( typically 30-50') costing less than £20k. Until now, the cheapest stabiliser systems, gyro or fins, have been around £50k and aimed at boats over 50', although Seakeeper have also reduced prices in this range to £40k at the same time as improving performance.

They are a fairly easy OEM fit, so i'd expect to see them on new boat options lists for about £30k, which is not a big cost for someone speccing a new 50' gin palace.

http://www.seakeeper.com/products/seakeeper-5

I've no links to Seakeeper other than as a satisfied customer.
 
Whitelighter said:
How well do the gyro stabs work compared to fins?
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I've not had a boat with fins so can't do a direct comparison. For us, stabilisation is not about passage making in heavy seas, it's about comfort at anchor or displacement cruising, and for this purpose a gyro wins hands down IMO. That's not to say a gyro isn't effective in bigger seas, it certainly is, but I can see that in some sea states fins could be better.
 
At the lower end of the size range and for retrofit, yes, packaging and maybe even weight could be an issue, but of course on new models they can be designed in, as happens now with larger boats.

The noise issue is that you have to run the genny, the unit itself makes virtually no noise.
 
Nick_H said:
For us, stabilisation is not about passage making in heavy seas, it's about comfort at anchor or displacement cruising, and for this purpose a gyro wins hands down IMO.
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I must disagree that in these conditions gyros win against fins, let alone hands down.
There's no such thing as a sea condition, neither cruising nor at anchor, where gyros can be more effective than fins. Gyros can be, at best, ALMOST as effective as fins. Possibly to the point of making the difference negligible in some conditions, which is great, but that's it.
Besides, it doesn't take storm sea conditions to reach the intrinsic limits of gyros: when pootling in quartering sea with a long swell, the boat can have a tendency to list for quite some time, either side, "following" the swell, so to speak. It's a type of movement different from the typical rolling, which is mostly driven by the natural hull frequency, but still pretty uncomfortable. In these conditions, gyros are unable to create a constant righting force, which is required to keep the hull flat, against the swell-induced listing. Something which fins can do very effectively, and practically forever.

Having said all that, there are other pros and cons of course, and as always with boats, it's a matter of choosing the best compromise.
I've always said that I'd rather have a gyro than a couple of fins sticking out of the hull, on any boat capable of 30+ knots, and I rest my case.
In this respect, Seakeeper definitely have their place in P boats market, and this new small unit makes good sense indeed.
Btw, I can imagine that it might be a good choice also for bigger vessels, with multiple units.
 
Nick_H said:
Seakeeper have announced a new gyro stabiliser for boats up to 20 tonnes ( typically 30-50') costing less than £20k. Until now, the cheapest stabiliser systems, gyro or fins, have been around £50k and aimed at boats over 50', although Seakeeper have also reduced prices in this range to £40k at the same time as improving performance.

They are a fairly easy OEM fit, so i'd expect to see them on new boat options lists for about £30k, which is not a big cost for someone speccing a new 50' gin palace.

http://www.seakeeper.com/products/seakeeper-5

I've no links to Seakeeper other than as a satisfied customer.
Click to expand...

Wow. That's a big price reduction on the existing (M7000?) unit, and the new unit does look attractive, although it's still nearly 400kg in weight. Interesting stuff though.
 
Thanks Nick - yes, agreed, that is a game changer. Till now stabilisation has hardly been practical at 40-50 feet but this changes everything. If I were SunPrinFair I'd have this on my options list right now for the 40-55 foot part of the range

The maths of gyro stabilisation contains many non linear relationships. This new small stabiliser makes up for a lot of its mathematical disadvantages by having a very high RPM, which is made possible by the lower mass of the gyro. The downside of the higher rpm is long spool-up time, but otherwise the performance stats look pretty good

At anchor, small boats are arguably harder to stabilise than bigger boats, because their much lower angular momentum gives them very short roll times. On a smaller boat, by the time the gyro or fin has figured out what to do the roll might be well on its way through its cycle. No doubt Seakeeper have handled this with fast computing and the right algorithms, but it would be interesting to try one of these on a 40 footer to see how well they've done

The power draw of this thing means it could be run underway with no genset, using an inverter, just by fitting big enough alternators (it needs 90 amps at 24v). That's pretty appealing too

Anyway, great product and I hope it takes off (figuratively speaking!)
 
MapisM said:
Having said all that, there are other pros and cons of course.
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?? I didn't say on which pros and cons my judgement was based.

I think gyros are better for use at anchor because they don't have fins sticking out of the side with a risk, albeit slight, to swimmers, and more importantly the boat doesn't paddle forward in light winds. I think they're better for pootling in slight to moderate seas because you get similar performance to fins without the trade off of extra drag at planing speeds. I know fins can be better in a quartering sea, that's why I said "in some sea states fins could be better", but I don't find that motion too uncomfortable in slight to moderate seas, so again I wouldn't trade off the loss of a knot at planing speed. In bigger seas the limits of the gyro are likely to be reached more often, so if I was passage making regularly in such seas then i'd sooner have fins.
 
Nick_H said:
?? I didn't say on which pros and cons my judgement was based.
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Well, you said "it's about comfort at anchor or displacement cruising", so I assumed that's what your judgement was focused on.
And comfort strictly depends on the sheer stabilization performance, obviously.
You're only now mentioning other factors, which is fine, but that's not the point I was disagreeing with! :)
 
MapisM said:
I must disagree that in these conditions gyros win against fins, let alone hands down.
There's no such thing as a sea condition, neither cruising nor at anchor, where gyros can be more effective than fins. Gyros can be, at best, ALMOST as effective as fins. Possibly to the point of making the difference negligible in some conditions, which is great, but that's it.
Besides, it doesn't take storm sea conditions to reach the intrinsic limits of gyros: when pootling in quartering sea with a long swell, the boat can have a tendency to list for quite some time, either side, "following" the swell, so to speak. It's a type of movement different from the typical rolling, which is mostly driven by the natural hull frequency, but still pretty uncomfortable. In these conditions, gyros are unable to create a constant righting force, which is required to keep the hull flat, against the swell-induced listing. Something which fins can do very effectively, and practically forever.
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I agree 100% your comments about performance underway. Even a small tiny fin will always beat a big gyro underway. Not that a gyro is bad. The thing about a gyro underway is that there is a time limit point of a few seconds after which it can do no more. It stops precessing when it his the mechanical limit, and at that point there is no more stabilisation. You can have a more stabilisation torque for a short time period (2 seconds, say) or little stabilisation torque for a long period (6 seconds, say). But what you can never have with a gyro is what you want in a big sea: a lot of stabilisation torque for a long time. In contrast, a fin can give you that. A fin creates a big anti roll torque 24/7, with no time limit, if you want. So a fin is always better in larger waves, or medium waves with a long period

It is interesting how often this isn't understood. Last weekend I let a fin installer use my boat for a sea trial for a fin customer. The customer, a very nice guy but not an engineery type, brought along a captain of a Sanlorenzo 104 who reckoned he was a bit of an engineer. As we discussed gyros v fins and the limits of precession over a coffee, the captain said I was wrong. He said the gyro merely has to spin at 1000rpm and that alone creates the antiroll torque. The rocking backwards and forwards, as he called the precession, was to help counteract pitching. Yes MapisM he said this! I suppose it is an understandable mistake when you look at a precessing gyro. When I told him the correct position he said "Well I've had a career as captain of a 100 foot boat so I know what I'm talking about". So, go figure! (I wont type here my response but as he was a hanger-on my boat I decided I had some freedom to choose the colour of it :D)

At anchor, you cannot answer the question "Which is better?" in a black and white way imho. You would need to define the rules for the comparison. As far as roll reduction is concerned, a big/good giro will beat a small/bad fin, and vice versa. The systems are so different that you will always struggle to define the rules for the comparison.

If you define the question as "what is best stabilisation for kg of weight installed of €€€ spend?" then they are pretty equal. If the question as "which is the smallest installation" then fins always win. If you don't want hull appendage, giros win. If you do not want the boat to swim forward on fins in light wind, gyros win.

But if you get back to the basic question of "which is better at reducing roll at anchor" then you cannot answer it without specifying some other parameters. My fins will always beat a Seakeeper 9 at anchor, but not a pair of Seakeeper 16s

My builder will install either so I had a free choice. I consciously chose fins because, primarily, they are much better in a big beam sea and they are about equal at anchor. As secondary reasons (a) the gyros eat up interior room (b) have a longer spool up than I'd like (c) require genset running underway, and I prefer to do long passages with genset off and have specced the boat to achieve that

In the video below the waves are massive, even though they look smaller on video. This was force 7-8 beam sea, 100+ miles fetch, day 3. If you look at the teak rail along the transom you can see there is ZERO roll on the boat. There is no way gyros could achieve this, no way at all. Only fins could do that. That's why I chose fins. But not everyone wants this, and if your priority is at-anchor stabs then gyros make a huge amount of sense. So there is no clear answer to "which is better" imho
 
jfm said:
As secondary reasons .... (c) require genset running underway, and I prefer to do long passages with genset off and have specced the boat to achieve that
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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.
 
Stupid question time. Can you combine 2 or more gyro stabs and if so, why would you buy 1 x S16 at $89900 as opposed to 2 x S5 for $59800? The combined anti rolling torque of the 2 x S5 is about the same and the total weight is less. Also having 2 smaller gyros would give you the option of running just one off an inverter in slight sea conditions and of course, if one breaks down, you still have the other. In addition, on some boats it might be easier to install 2 small gyros than 1 big one
 
@Nick post #15. Yup. I was explaining merely secondary reason for my particular choice though, and I'd need 2x 8000, and in a big sea when the precession is quick and fast you might see much of power draw taken by the precession hydraulics (I don't know the data here, but alas when speccing a boat you do find yourself using the stated figures to be safe side!). But yes, I see from your real data that you could delete my reason (c) :)

I don't have a bad word t say about seakeepers. They're brilliant things, from a nice company with integrity. They're substantially better than the gyro competition in this space (namely mitsubishi and the italian firm whose name I forget). The problem with stabilisation is that you need to make an intelligent choice between fin and gyro based on your own parameters. The manufacturer's don't make the comparison well; they just blurt out "ours is best" and badly informed people (present company of course excluded, but my Sanlorenzo guy at the weekend very much included!) say "gyro is best" or "fin is best". It's only on here imho that there is a candid discussion of the pros/cons of each type of stabiliser! :D
 
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.
 
jfm said:
The problem with stabilisation is that you need to make an intelligent choice between fin and gyro based on your own parameters. The manufacturer's don't make the comparison well; they just blurt out "ours is best" and badly informed people (present company of course excluded, but my Sanlorenzo guy at the weekend very much included!) say "gyro is best" or "fin is best". It's only on here imho that there is a candid discussion of the pros/cons of each type of stabiliser! :D
Click to expand...

Yep, and your post #14 was a great summary of the pros and cons, all of which I agree with.
 
Deleted User said:
Stupid question time. Can you combine 2 or more gyro stabs and if so, why would you buy 1 x S16 at $89900 as opposed to 2 x S5 for $59800? The combined anti rolling torque of the 2 x S5 is about the same and the total weight is less. Also having 2 smaller gyros would give you the option of running just one off an inverter in slight sea conditions and of course, if one breaks down, you still have the other. In addition, on some boats it might be easier to install 2 small gyros than 1 big one
Click to expand...

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
 
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