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

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jfm

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The immense growth in popularity of stabilisation over the last few years is creating some nice (for us, the customers) pressure on manufacturers to be really smart, which is great news. I see that Sidepower/Sleipner have now gone public on their new curved fins (called "vector fins"). These are game changers, and patented so will be hard for others to copy. They were at Cannes boat show and are in the new issue of MBY, reviewed by Greg. I had the pleasure of seeing the drawings and other info (lots of maths!) several months ago, before the patent was filed, and I'm pleased for Sleipner that they have now got to the stage of full launch

The fins are basically curved outwards
vectorfins.jpg


The curve changes the direction of the antiroll vector and the length of its lever arm about the ship's roll axis, and makes the fin perform as if the boat had a 40 degree deadrise not 20, or whatever. It's a case of a brilliantly simple idea combined with clever manufacturing to be able to construct the thing (the challenge being that there can be no full length shaft passing through the fin, of course).

They will have hydraulic actuation only for foreseeable future I believe, but in new build that's fine - Robg71 take note! (Needless to say, in retrofit projects electric may often be an easier choice, as with BartW's Blue Angel).

Now, as interestingly, Sleipner have also launched a new actuator with dual hydraulic cylinder working in rack and pinion mode rather than via tiller arms, and this creates a very compact installation so these can be installed in the mid-50 footer bracket, maybe 50 footers. The first ones are already in a 2013 Princess 56.

The combination of very small actuators and curved fins could make the whole idea of fin stabilisation far more appealing to 50-60 footers and anyone thinking about buying in that size should consider these very carefully imho

Detailed info here http://www.side-power.com/public/vectorfins/vectorfins.pdf
 
shame theres no more details than the pdf. nothing on the website i could find for weights and specs, but this certainly looks like a more suited product, rather than something from a much larger vessel.
Thanks a million for the find, I owe you a beer.... or ten.... :)
 
a neat development of standard 'straight' fins, but it started me thinking of fish, which have two pectoral fins, and (generally) two pelvic fins.

Currently boat stab fins seem to be more like pectoral fins than pelvic ones.

Pelvic (underneath) and adipose (on top)/ventral (underneath) fins are understood to be the controllers for roll stabilisation, and pectoral for station-keeping and some propulsion (ref jfm's thread on Match 'creeping').

Do any of you advanced mobo people know of any work on fins which imitate adipose/anal fins, and would therefore be located more in a vertical orientation rather than the 45(ish) degree down ones of the current commercial offerings. Probably next generation stuff.
 
Those stats are impressive, sounds a great solution for P52 / P56 where internal space limited for gyros (although apparently possible when I asked at SIBS).

Wonder if Princess use an electric motor to power hydraulic pump, the 13.5KW Onan supports PTO but space for pump next to genny could be a problem?

Anders
 
Two thoughts (one or other of which may show my ignorance of the physical world):

1 Would it be possible to put some articulation in the middle of the fins so that the tips described a much larger curve than the bases? This would be more like a fish's fins.

2 Instead of curving the fins outwards would the same (or similar) effect be achieved just by angling straight fins more outwards?
 
These new fins from Sleipner are very clever, perhaps a game changer in the fin stab market. I love that such a simple change in design (not manufacture) can give such a large advantage. It's now so clear and quite obvious how the efficiency increases over traditional fins that the competition must be kicking themselves. Reminds me of Dyson.
 
MYAG said:
It's now so clear and quite obvious how the efficiency increases over traditional fins
Click to expand...
Well, if it is, I must be be duller than I thought, 'cause I don't get it at all.
In my books, fins are supposed to work in both directions, so whatever is gained in one (if anything) is lost in the other, surely?
 
MapisM said:
Well, if it is, I must be be duller than I thought, 'cause I don't get it at all.
In my books, fins are supposed to work in both directions, so whatever is gained in one (if anything) is lost in the other, surely?
Click to expand...

I'm also thick and don't understand the benefit of a curved fin.
 
longjohnsilver said:
I'm also thick and don't understand the benefit of a curved fin.
Click to expand...

me 3 :rolleyes: ,

a elaborate video/forces diagram showing how the one vs the other work would be nice to get it.

BTW, if there was space to put the axle of thes stabs horizontal, would that make them even more efficient? (forget issues with mooring, extending over the beam of the craft etc, just a theoretical Q to help me understand this curving thing)

cheers

V.
 
Here's my guess, and its nothing more than a guess. If you think of the boat as being a cylinder, then I'd have expected the optimum anti rolling force with the fins axle being normal to the cylinder (the normal being a line which passes through the circumference and the centre point of a circle). Now most boats have modest deadrise at the point where the fins would be mounted, so the axle would actually be in line with a point well above the centreline of the cylinder, but bending the fins means that some of the fin is operating at the most effective angle. I put this forward with little or no conviction :D
 
"normal"= diameter or 1/2 that radius .

Chaps -nowt new here Fins are fins on a small boat 56ftr you will need smaller fins than a larger boat 78 ftr -agree?
Previous ltd factor has not been fin size -it's been actuator and all the other internal gubins to move the fins .
Bart has fitted an electrical system to overcome this space issue.
Here they have made simply smaller and probably faster hydraulic actuators to overcome the space or lack of it to fit -issue -to package them in smaller hulls.
At the same time come up with curved fins -marketing ?? Ah well keeps the shareholders happy:;)
I suspect bogo flat ones for a 56 ftr would not be that much larger so,s that any one will notice the difference at sea ?.
 
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Yeh look at the pics agian
Mentally fit the curved fins to a hull - roll it to one side -now mentally think of the curved tips
One due to the curve is actually more helpful ,but t,other equally (cos curve is in the wrong direction) is worse / unhelpful
Then as if both would have been if both were simply straight .
Breakthrough is smaller packaging that's all .
 
Portofino said:
"normal"= diameter or 1/2 that radius
Click to expand...

eh?? Diameter and radius are distances, the term "normal" simply relates to lines crossing each other at 90 degs (ie. one is normal to the other). When considering circles, or cylinders viewed end on, the "normal" is a line perpendicular to the tangent and will always pass through the centre of the circle. It has nothing to do with distance.
 
MapisM said:
Well, if it is, I must be be duller than I thought, 'cause I don't get it at all.
In my books, fins are supposed to work in both directions, so whatever is gained in one (if anything) is lost in the other, surely?
Click to expand...
You're right that the need to work in both directions at anchor, but blimey it's surely obvious that benefit of the curve works in BOTH directions
 
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