Game changer from Seakeeper?

[Nick_H]

Depends on the boat, mine cost 15000 euro to fit, which included moving a bulkhead, and that's in the SoF. Fitting it is actually very easy, crane it in, glue it to the bearers, wire up 24 and 240V, wire control panel in suitable location, fit a raw water feed and drain, and off you go. It's making space and getting access that costs money for retrofit, but that's obviously not an issue for OEM fit if the boat is designed to take one

 

[MapisM]

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?

Actually, fins are not meant to generate lifting forces, but rather forces as tangent as possible to the hull rolling axis.
Which you can indeed split in a vertical (either up or down) component, but that's incidental, and none of this has a lot to see with your question anyway.
So, I hope you'll forgive me for digressing a bit...

Back to the point, nope, fins at zero speed don't depend on any water flow, and simply rely on brute force, so to speak.
Since you mentioned hydrofoil, I guess you are thinking that the fins rotate around shafts positioned just about in the center of each fin.
This was true for old stab systems (like the one I've got in my boat btw), meant to work only while under way.
In modern zero speed fin stabs, shafts are positioned much more towards the front of each fin.
This doesn't make any meaningful difference in the way they work while under way - aside from the fact that they obviously require a bit more power, compared to systems where the fin rotation is self-compensated, if you see what I mean.
But it makes a huge difference at anchor, because the forward shaft position means that when a fin suddenly and quickly rotates in one direction, most of the fin surface has to fight the water resistance, hence creating a force which pushes the hull in the opposite direction.
Yeah, but the same applies when the fin, sooner or later, has to return in its center position, I hear you saying. Which is true, but by the time the fin reaches its maximum extension, also the rolling is probably going to reverse, so the fin can actually stabilize the boat also when it's on its way back - it's just a matter of waiting the moment when the roll begins reversing.
Otoh, if the first slap is sufficient to stabilize the roll, the fin will simply return to its center position slowly enough to not create any meaningful rolling force.

Of course, behind all that, there's a great deal of sensors and processing power, to a) capture and measure as soon and as accurately as possible each boat roll, b) compute the optimal fin actions that such roll requires, and c) eventually make the fins execute these actions.

I'm not sure to have clarified your doubt, but I did try!

 

[vas]

Of course, behind all that, there's a great deal of sensors and processing power, to a) capture and measure as soon and as accurately as possible each boat roll, b) compute the optimal fin actions that such roll requires, and c) eventually make the fins execute these actions.

I'm not sure to have clarified your doubt, but I did try!

A few thoughts if I may:

A car ECU does a hell of a lot of processing and is typically around 1k
Sensors are probably in the 1k region (although should really be 100euro max!)
El.motors and gearboxes I've no idea, depends on sizes but 1k should really cover each side.

Shaft/seals I guess they have sussed it by now...
Fins, no comment
So, exclusive, low volume, mid (to low) tech product markup, dunno 1k% {funnily enough 1k seems to be a recurring value)

Slight tongue in cheek I still believe for a 40-50 footer a say 250x600mm set of fins should be under 20k...
And that obviously will not have Match performance but getting an uncomfortable anchorage to acceptable levels should be doable

Cheers
V.

 

[JumbleDuck]

Actually, fins are not meant to generate lifting forces, but rather forces as tangent as possible to the hull rolling axis. ... I'm not sure to have clarified your doubt, but I did try!

Many thanks ... that's very clear. When I said "lift", by the way, I was using it in the fluid dynamics sense of "a force at right angles to the free stream flow" so in the circumstances it's the same as your "forces as tangent as tangent as possible ..."

 

[MapisM]

A few thoughts if I may

Can't disagree with all that, V.
My sentence which you quoted was not meant to justify the cost, in fact.
Otoh, what you're saying is true for just about anything in pleasure boats market.
Justify me a cost of 600 Eur for ONE of these things, if you can.....

 

[MapisM]

Many thanks ... that's very clear. When I said "lift", by the way, I was using it in the fluid dynamics sense of "a force at right angles to the free stream flow" so in the circumstances it's the same as your "forces as tangent as tangent as possible ..."

Thanks to you for the wording clarification, I wasn't aware of that, and I always associated "lft" to an upward force, as the one which makes the boat plane.
In hindsight, I can see that it's exactly the same type of effect with fin stabilizers, rudders, etc.

 

[rubberduck]

It all seems a bit like the 1st flat screen TV's etc, start off at ridiculous prices & then come steadily down to a reasonable margin.

 

[kashurst]

It seems to me on new boats the seakeeper models or an equivalent priced fin system would be a definite selected option in future, but secondhand boats are approximately half the cost of a new one and second hand boat owners are usually running them at a lower cost as well,
so what would you, as boat owners, be prepared to pay for a retro-fitable stabilizing mechanism for your size of boat ?

 

[rubberduck]

Lets see where it ends up, sub 20k,

 

[Deleted User YDKXO]

Can't disagree with all that, V.
My sentence which you quoted was not meant to justify the cost, in fact.
Otoh, what you're saying is true for just about anything in pleasure boats market.
Justify me a cost of 600 Eur for ONE of these things, if you can.....

Still thinking about those things, Mapism? Go on, you know you want to

 

[Hurricane]

Sorry guys, I just dont see the need for ANY kind of stabiliser.
On the few ocasions where we would have benefitted from stabilisers, there were other options.
If the sea is too rough for pootling, then we pop onto the plane and get where we are going quicker - and the boat's design basics are for planing so she is inheritanty more stable planing anyway.
If an anchorage becomes too swelly, then we move somewhere where there isnt a swell - in the cruising areas we have been in the last 6 years, there has generally been an option to move to a calmer anchorage.

Having said that there have been a few (very few) times when we would have benefitted from stabilisers. Not enough to justify the cost, mind you, but lets suppose thaI wanted to retro a gyro system. I wouldn't want to use my laserette - it is used too much for other things.
I, do however, have a huge bilge area under our main (centre cabin) bed - where JFM has his spare fuel tank. Would this be a feasable place for a gyro system?

 

[Elessar]

Sorry guys, I just dont see the need for ANY kind of stabiliser.
On the few ocasions where we would have benefitted from stabilisers, there were other options.
If the sea is too rough for pootling, then we pop onto the plane and get where we are going quicker - and the boat's design basics are for planing so she is inheritanty more stable planing anyway.
If an anchorage becomes too swelly, then we move somewhere where there isnt a swell - in the cruising areas we have been in the last 6 years, there has generally been an option to move to a calmer anchorage.

Having said that there have been a few (very few) times when we would have benefitted from stabilisers. Not enough to justify the cost, mind you, but lets suppose thaI wanted to retro a gyro system. I wouldn't want to use my laserette - it is used too much for other things.
I, do however, have a huge bilge area under our main (centre cabin) bed - where JFM has his spare fuel tank. Would this be a feasable place for a gyro system?

There're lots of things on a boat you don't NEED. Including the boat!

 

[Deleted User YDKXO]

Sorry guys, I just dont see the need for ANY kind of stabiliser.

I sort of agree with you. Nobody really needs stabilisers. They're just another of those things that make life on board a bit more comfy than it would be otherwise. Before I spent summer in Sardinia I might have agreed with you on the need for stabilisers at anchor but when every anchorage is blighted by idiots speeding in, out and through them without a care for anybody else, stabilisers would have been really useful. The same goes with pootling. Several times this year I've been pootling along but have had to speed up to get some roll stability when I didn't want to and when diesel costs €1.80/l as it does in Italy, that becomes irritating. Lastly I think the other guys are right about getting your money back when you sell your boat. A boat with stabilisers is going to sell quicker and for more money than the same model without them.
With regard to where to place a gyro, other more knowledgeable forumites will I'm sure comment but as far as I understand, they need to be placed as far aft as possible in order to minimise pitching movement. I think I read somewhere that the Seakeeper will actually shut down if it senses too much vertical movement

 

[benjenbav]

I sort of agree with you. Nobody really needs stabilisers. They're just another of those things that make life on board a bit more comfy than it would be otherwise. Before I spent summer in Sardinia I might have agreed with you on the need for stabilisers at anchor but when every anchorage is blighted by idiots speeding in, out and through them without a care for anybody else, stabilisers would have been really useful. The same goes with pootling. Several times this year I've been pootling along but have had to speed up to get some roll stability when I didn't want to and when diesel costs €1.80/l as it does in Italy, that becomes irritating. Lastly I think the other guys are right about getting your money back when you sell your boat. A boat with stabilisers is going to sell quicker and for more money than the same model without them.
With regard to where to place a gyro, other more knowledgeable forumites will I'm sure comment but as far as I understand, they need to be placed as far aft as possible in order to minimise pitching movement. I think I read somewhere that the Seakeeper will actually shut down if it senses too much vertical movement

Having been onboard jfm's Match 2 with 30-40 others - some carrying alcoholic refreshments, some wandering about, some doing both at the same time - with the stabs keeping the whole affair as rock steady as the groove on the sound and light systems I have to say I think they're absolutely necessary.

 

[Nick_H]

With regard to where to place a gyro, other more knowledgeable forumites will I'm sure comment but as far as I understand, they need to be placed as far aft as possible in order to minimise pitching movement. I think I read somewhere that the Seakeeper will actually shut down if it senses too much vertical movement

It's g-forces from slamming that causes the issue, therefore Seakeeper reccommend they are not placed too far forward, and yes, the unit will shut down if the g-forces exceed the limit. I'd have thought that under a mid cabin bed would be fine though, if space allowed.

 

[Deleted User YDKXO]

Having been onboard jfm's Match 2 with 30-40 others - some carrying alcoholic refreshments, some wandering about, some doing both at the same time - with the stabs keeping the whole affair as rock steady as the groove on the sound and light systems I have to say I think they're absolutely necessary.

bjb, it would indeed have been tragic if you had spilt your Martini cocktail. As good an argument for stabs as I've heard

 

[Hurricane]

I've been on Match (Match 1 in fact) in Antibes when they were testing the original stabilisers and. yes, they were impressive.
We were in seas bigger than I would have been comfortable in JW
In fact I wouldn't have bee in those seas at all and the stabilisers were working well.
However, I still find it difficult to justify that kind of money.

After this season, higher on my list of priorities is a water maker - I might make it a winter project and build one.

There're lots of things on a boat you don't NEED. Including the boat!

And Mark - you CAN go boating without stabilisers but you CAN'T go boating without a boat.

 

[jfm]

we pop onto the plane and get where we are going quicker - and the boat's design basics are for planing so she is inheritanty more stable planing anyway.
.....
I, do however, have a huge bilge area under our main (centre cabin) bed - where JFM has his spare fuel tank. Would this be a feasable place for a gyro system?

a planing boat actuay planing is still way more roll free with fins than without

Under mid cabin bed is fine as far as stabilisation is concerned but you have a major challenge getting the thing into the boat, down the stairs and through a 480mm wide door.

 

[jfm]

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.

you do not force it to precess on a leisure boat gyro. Instead, the waves force it to roll, it then naturally processes, and exerts an anti roll torque. IF you did force it to precess then it would exert a roll torque on the hull, but outside of big ship gyros these are not forced/ induced precession devices

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.

The first sentence is correct but isn't relevant ( except as noted below ref damping) because these things are not inducing precession. The second sentence isn't correct: if you let a gyro precess naturally and a wave rolls the boat, the gyro will produce an anti roll torque WITHOUT any pitching torque. There cannot be a pitching torque because the gyro is on bearings and therefore isn't connected to the hull in a pitching sense
Now if you add the hydraulic cylinder that induces or damps precession, you do indeed then have a pitch torque on the hull. But the amount is tiny. Absolutely minuscule. The athwartships gimballing of the gyro means that you have blocked it from precessing so you get no " multiplier" effect from the gyro's spin. Thr gyro might as we'll be doing zero rpm. You therefore have just the mass of the gyro and its casing, and a 0.5 m lever arm versus a 20m hull. You would quite literally get more pitching torque in the hull if you got a small dog and trained it to run to the bow when the bow pitched up and to the stern when the bow pitched down

I really don't see how you can get a gyroscope to produce a rolling moment only.

it does, if you let it precess freely

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.

I'm assuming the second "and" is meant to be "around" Yes the wave action is the torque applied around the fore- aft axis ( if that's what you meant?) and the gyro produces anti roll torque around the same axis PROVIDED it is allowed to precess

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.

absolutely not. If you let the gyro precess, there is no pitching moment or pitching torque created by the gyro. None at all. There can't be because the thing is mounted on bearings in the pitch sense. The hydraulics are there to damp/ slow down the precession so as to make best use of the gyro, ie to slow down the precession and make the stabilisation effect last longer. As explained above the hydraulics themselves create a pitch torque ( action= reaction) as they slow or block the precession, but the amount is tiny because the gyro is blocked from precessing about a fore-aft axis so there is no " gyro effect / gyro multiplier" on the pitching torque and my dog analysis above applies

 

[MapisM]

Still thinking about those things, Mapism? Go on, you know you want to

LOL, yeah, I do like them.
And TBH, a dozen of hundreds eur ain't a life changer amount, in the great scheme of boating costs - particularly if they would actually avoid some boat damages in a storm.
It's rather a matter of principle: I don't like the idea of supporting the business of anyone who thinks there's nothing wrong in ripping off customers, just because some of them don't care about it.....