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

[jfm]

Hold on a minute! What the h*ll is going on in that video? The boat is not being moved by the water. It's not at anchor, it's alongside in a marina which seems to be flatter than a mill pond on a flat calm day. To make the boat roll like that I suspect a weight (possibly people) was being moved from side to side. Stopping this is what stopped the roll not the fins! I certainly wouldn't take this video as evidence of the effectiveness of fins when stationary. Show an anchorage where every boat is rocking and rolling and the finned boat is as stationary as the Isle of Wight that would be a more effective marketing tool. If the boat in the video is being rolled like that by the sea in those conditions then someone needs to do some serious stability calculations fast!

That's a Sq78. Just in the engine room, there is 8 tonnes of cast iron with Caterpillar stickers on. Midships there is 7 tonnes of fully baffled fuel. Then there's a hull, deck, some furniture and a lot of wine. Call it 60 tonnes. This is all quite funny but would you give me another laugh and tell me how many people, to the nearest 25, need to run from side to side in the saloon to make it roll like that?

 

[cryan]

no, if there is water movement over the fins, maybe even imperceptible, the boat will induce roll, if told to do so....
we had to test the anti heave on a 22000ton DSV in relative calm water. If you can stop roll, you can also induce it just as easily.....

JFM, if thats 50% im really impressed considering its as flat as a witches tit really....

As stated above I misunderstood what I was seeing. and so have deleted the post.

I have also been through system tests on anti roll tank systems on both offshore boats and cruise ships. yes you can obviously induce a roll and the video is impressive in that matter. however how much is the vessel usually rolling at anchor that this system is required?

 

[cryan]

That's a Sq78. Just in the engine room, there is 8 tonnes of cast iron with Caterpillar stickers on. Midships there is 7 tonnes of fully baffled fuel. Then there's a hull, deck, some furniture and a lot of wine. Call it 60 tonnes. This is all quite funny but would you give me another laugh and tell me how many people, to the nearest 25, need to run from side to side in the saloon to make it roll like that?

As stated above I misunderstood what I was seeing. and have deleted the post.

It is an impressive movement. As said before I don't doubt the ability under way. Having been through trial on offshore boats looking for a way to make cargo snatching safer. It was found t hat fin stabs were of little use under station keeping conditions. However that was due to the time it took for the actuation to react. In such small systems as on yachts this would not be as big an issue. The video is certainly impressive but as I stated above how much rolling do you see at anchor?

 

[jfm]

Sorry in the time it took to write that you have answered, Is it the fins movement that is causing the roll?

Ok Deleting previous post as I misunderstood what was happening in the video.

Just to clear up confusion D ) the fins are in "test mode" n the video. This is deep in the menus. You can set the angle of sweep and the sweep timing. In that video they are sweeping +/- 20degrees (= about half the maximum), with a sweep every 5 seconds (= much less than full speed). As Rob said, if they can induce that roll, they can also eliminate it (given perfect control of course). I could have "turned up the volume" and easily rolled it more than in that video. These are seriously effective things, and I put up the video to contradict your "I'm still not convinced that the effect at anchor will be that great as you are relying on the passive effect of small fins." I hope you are now convinced!

 

[jfm]

Having been through trial on offshore boats looking for a way to make cargo snatching safer. It was found t hat fin stabs were of little use under station keeping conditions. However that was due to the time it took for the actuation to react. In such small systems as on yachts this would not be as big an issue. The video is certainly impressive but as I stated above how much rolling do you see at anchor?

You must having been using junk gear in your test. Virtually all superyachts, including the 80-90-10+metre stuff, have for >10 years had very effective zero speed fin stabilisation made by Quantum and others. It is undisputed that this gear is hugely effective, if you install the correct gear. The water tanks/flumes that Feadship had a great expertise in went out of fashion perhaps 15 years ago, because fins got so good and those sytems ate up huge amounts of space of course

Actually we see plenty of rolling at anchor (in the Med). Not huge angles of roll, but enough to make some more sensitive guests perhaps seasick, and the stabilisers eliminate this almost entirely. I'm not saying there is any need to eliminate this roll, because it is mild, but it is very nice to eliminate it. We're in a world of luxury/hobby boating here, not commercial boating, of course, and in the same vein we probably have better hifi than commercial boats. BartW, Nick-H and and MYAG on here have STAR boats and will I think say the same. The FDC is currently on a fin stabbed STAR boat, and MapisM was singing the praises of these fins a few days ago. Also in the Med you lie at anchor to the wind but if you're in a bay the swell can turn a corner as it enters the bay. It's therefore common to lie to the wind and have the swell on your beam. Villefranche is a famous and typical example. STAR is fantastic in these conditions

 

[cryan]

Just to clear up confusion D ) the fins are in "test mode" n the video. This is deep in the menus. You can set the angle of sweep and the sweep timing. In that video they are sweeping +/- 20degrees (= about half the maximum), with a sweep every 5 seconds (= much less than full speed). As Rob said, if they can induce that roll, they can also eliminate it (given perfect control of course). I could have "turned up the volume" and easily rolled it more than in that video. These are seriously effective things, and I put up the video to contradict your "I'm still not convinced that the effect at anchor will be that great as you are relying on the passive effect of small fins." I hope you are now convinced!

Oh your doing a good job!
Don't take anything I say as aggressive etc. As a Marine Engineer I have an almost anorak interest in new marine tech but as an engineer I MUST question everything before accepting anything. If this system can keep the pink in a gin glass then all the better.

 

[Groot T]

.. and a lot of wine.

Now wine which needs time to settle. Poor bottles. Though that is why you put stabs on there in the first place ?!

But in all seriousness, very interesting thread and very well done to the chaps at Sleipnir. Forgive me for asking a silly question, I can see why this is such a huge plus for the smaller boats though is there a plus for larger boats, i.e. over 60 feet?
Also, do you have them on your boat, JFM?

 

[Robg71]

Now wine which needs time to settle. Poor bottles. Though that is why you put stabs on there in the first place ?!

But in all seriousness, very interesting thread and very well done to the chaps at Sleipnir. Forgive me for asking a silly question, I can see why this is such a huge plus for the smaller boats though is there a plus for larger boats, i.e. over 60 feet?
Also, do you have them on your boat, JFM?

already specced for 'Match 3'

 

[Portofino]

Another very important point especially for smaller boats, where people have mentioned above that the main benefit is just the compact actuator. In a small boat, say a 50 footer compared with an 80 footer of the same genre, you generally have a much shorter/faster natural roll. To have effective STAR, you need more stabilisation force relative to the boat's weight than in a big boat

This means that the effect of yaw is greatly increased. Think of the boat's roll axis as a big bearing about which the boat rolls, but then remember that bearing is really sloppy because it is just the boat's inertia, nothing else. As the fins sweep left/right at anchor, the whole boat shudders/jerks sideways. This is almost imperceptible in and 80 footer weighing 55-60 tonnes, but it is a very big deal (as regards comfort) in a 50 footer weighing 16 tonnes

Now, if you had Nick-H's theoretical boat with a cylindrical shape of even density, the fins would produce only perfect anti-roll forces if mounted centrally along the hull's length. The line of the shafts of the fins would intersect the roll axis, so the antiroll vector would be a tangent to the circular section of Nick's boat, which is perfection. But none of our boats are like that, and the direction of the antiroll vector from the fins is not tangential to Nick's cylinder. Hence in the real world you get sway (ie sideways jerks of the hull as the fins sweep), and in addition you get yaw (where the boat's heading alters, ie it turns left right as the fins sweep) if the fins are not perfectly centred in a fore-aft direction, which they won't be. These new curved fins significantly reduce these nasty side effects, which is a big deal in the 50-footer segment. I mean the lightweight 50 segment where boats weigh 15 tonnes or whatever

Yeh I can buy into to " reduce nasty side effects " That's the real reason for the curved fins

And as agreed the packaging for smaller boats helps
And prob less inertia + faster - needs to be due to low mass 16 T or lower

But what's gained on a concave surface of one is lost on the convex of the other .cannot see BOTH beneficial-but that works in small boats
As you say small light boats with straight fins could end up jerking about .
These do not ( or minimise)Jerking because the convex -active one slips water .
Big boats ( not sure how to define that) + ships will function perfectly with straight fins

The 70k bit -how much is sea keeper gyro as a cost comparison ?

 

[cryan]

You must having been using junk gear in your test. Virtually all superyachts, including the 80-90-10+metre stuff, have for >10 years had very effective zero speed fin stabilisation made by Quantum and others. It is undisputed that this gear is hugely effective, if you install the correct gear. The water tanks/flumes that Feadship had a great expertise in went out of fashion perhaps 15 years ago, because fins got so good and those sytems ate up huge amounts of space of course

Actually we see plenty of rolling at anchor (in the Med). Not huge angles of roll, but enough to make some more sensitive guests perhaps seasick, and the stabilisers eliminate this almost entirely. I'm not saying there is any need to eliminate this roll, because it is mild, but it is very nice to eliminate it. We're in a world of luxury/hobby boating here, not commercial boating, of course, and in the same vein we probably have better hifi than commercial boats. BartW, Nick-H and and MYAG on here have STAR boats and will I think say the same. The FDC is currently on a fin stabbed STAR boat, and MapisM was singing the praises of these fins a few days ago. Also in the Med you lie at anchor to the wind but if you're in a bay the swell can turn a corner as it enters the bay. It's therefore common to lie to the wind and have the swell on your beam. Villefranche is a famous and typical example. STAR is fantastic in these conditions

I wouldn't say it was junk gear (Rolls Royce etc) but there is quite a substantial difference between an anchorage in Monaco and supplying offshore installations in the winter.
Tank systems were found more effective and nowadays they are making changes to bow shape and hull shape with varying degrees of success. The forces in those operations put far to much stress on the control gear. The past five years before starting up my own business I was involved in towage so instead of trying to minimise roll we were more interested in using it to increase bollard pull.

 

[jfm]

But what's gained on a concave surface of one is lost on the convex of the other .cannot see BOTH beneficial-but that works in small boats
As you say small light boats with straight fins could end up jerking about .
These do not ( or minimise)Jerking because the convex -active one slips water .
Big boats ( not sure how to define that) + ships will function perfectly with straight fins

The 70k bit -how much is sea keeper gyro as a cost comparison ?

It is nothing to do with convex versus concave and your statements just aren't correct. It is to do with the angle, ie the direction, of the antiroll vector that the fins create. That angle is closer to optimum with these fins than with flat fins. The improved angle works both when sweeping CW and CCW because it has nothing to do with concave/convex. I've explained this above so don't want to repeat that here, but it would be good to remember that in a static state the direction of the force exerted by a pressurized fluid on a solid object is ALWAYS perpendicular to the surface of the solid, which means the force vector is the same direction on both sides of the curved fin because the two sides, both the concave and the convex, are parallel.

I don't know the costs but they are quite similar as between gyros and fins. Both will be in the order of £70k on a 55 footer and £100k on an 80 footer. There are lots of variables of course, including the new build vs retrofit question.

 

[Portofino]

Wow, lots of good questions. I'll have a go at answering them. ---------
However, Sleipner have measured this carefully. The maths proves that (a) the reduction in magnitude on the CW rotation is less than the increase on the CCW rotation (relative to a flat fin) and (b) the reduction in the vector magnitude is more than compensated mathematically by the increased verticality of the vector's direction, so you are still ahead, overall net net, in both directions of fin rotation, compared with flat fins.

Get some more popcorn folks

" ( relative to a flat fin ) " t,other is convex -curved in the wrong direction - slipping water as the active one is concave -scouped .
But that accidentally helps reduce " nasty side effects"
You not ahead - deliberately behind cos boat has little mass ,relying on extra speed + clever CPU .

 

[jfm]

Forgive me for asking a silly question, I can see why this is such a huge plus for the smaller boats though is there a plus for larger boats, i.e. over 60 feet?
Also, do you have them on your boat, JFM?

Yes, the benefit on larger boats say 80 ft plus is the increased anti-roll effect (at anchor) from the same sized/same drag fin, or if you prefer the same antiroll effect from a smaller/lower drag fin. Or somewhere in between. The elimination of sway/yaw/jerkiness is less relevant for larger boats because they have less stabilisation force per tonne of boat due to their longer natural roll time. On my boat, I feel very little jerkiness - not zero, but very little

I don't have them on my boat because I was too early. I saw the designs and read the patent application (subject to a promise of secrecy, hence I'm discussing these only after Sleipner have launched these things publicly) at about the time my boat was being finished. Sleipner are only now making the curved 0.8metre squared fins that would fit my boat but there are some technical challenges about the retrofit that are not determined/decided yet, due to fact I have the earlier generation actuators. If we can overcome those I'll buy the curved fins and retrofit, and sleipner have offered to help all that. If not i'll put them on my next boat. I'll let you know about retrofitting when we get a decision

TOTALLY OFF TOPIC, I thought you'd like this picture Toby. We've had a lot of fun with the kahlenbergs and I'm so glad you persuaded me to buy them. They will be on my next boat for sure (I need to retake this pic when boat is clean - it is covered in red-rain marks, urgh)

 

[Portofino]

but it would be good to remember that in a static state the direction of the force exerted by a pressurized fluid on a solid object is ALWAYS perpendicular to the surface of the solid, which means the force vector is the same direction on both sides of the curved fin because the two sides, both the concave and the convex, are parallel.

" parallel " Therefore cancel each other out .

 

[jfm]

Get some more popcorn folks

" ( relative to a flat fin ) " t,other is convex -curved in the wrong direction - slipping water as the active one is concave -scouped .
But that accidentally helps reduce " nasty side effects"
You not ahead - deliberately behind cos boat has little mass ,relying on extra speed + clever CPU .

Portofino, despite the increased popcorn sales that might ensue , I'm not going to argue this with you. You do not understand the significance of the change in the direction of the antiroll vector, otherwise you would see that the convex side is the right direction not the "wrong direction". You don't understand the physics of this. Wait and see whether Pershings, Rivas, Fairlines, Princesses and your favourites, Sunseekers, etc have flat fins or curved fins in a couple of years time.

 

[jfm]

" parallel " Therefore cancel each other out .

Oh heck. How does that saying go: "Never argue with...." Oh never mind .

 

[Robg71]

we should have a 'like' button on here

 

[Nick_H]

The video is certainly impressive but as I stated above how much rolling do you see at anchor?

That depends where you anchor of course. I see you're based in Fife and it may well be that you either have very protected anchorages, or relatively few other boats creating wash, or both. In the South of France we have some wonderful anchorages, but they're generally completely open to at least one side, plus we have lots (and I mean lots) of big boats whizzing up and down the coast creating big wakes. I've had bottles smash in cupboards, plates flying off tables, and guests doing starfish impressions in the cockpit to brace themselves against the quite violent rolling you get when a big swell hits a lightweight mobo beam on. Wakes are a particular problem because it doesn't matter how calm and settled conditions are, you can always be hit by another boats wake, so you can never fully relax, unless of course you have stabilisers

 

[cryan]

That depends where you anchor of course. I see you're based in Fife and it may well be that you either have very protected anchorages, or relatively few other boats creating wash, or both. In the South of France we have some wonderful anchorages, but they're generally completely open to at least one side, plus we have lots (and I mean lots) of big boats whizzing up and down the coast creating big wakes. I've had bottles smash in cupboards, plates flying off tables, and guests doing starfish impressions in the cockpit to brace themselves against the quite violent rolling you get when a big swell hits a lightweight mobo beam on. Wakes are a particular problem because it doesn't matter how calm and settled conditions are, you can always be hit by another boats wake, so you can never fully relax, unless of course you have stabilisers

Here in Fife the anchorages are mostly commercial. The Forth is a very busy port. You don't get many yachts anchoring other than in harbours and club moorings and none are really of the size that would allow fin fitting. Most other anchoring is done by anglers who really are not that bothered by a bit of pitching. It is a different kind of leisure boating here really. I have been to a fair few Med anchorages whilst on cruise ships and I know you can get a swell which used to affect our tender operations but I would have thought that a big yacht on an anchor would have set fairly steady, perhaps some pitching?
Perhaps the real difference is the perception of what's acceptable. Having spent my life walking in serpentine lines around boats whether working or at leisure I don't really see a need for this type of system at anchor. However I may feel differently if I wanted to sunbathe or entertain guests. (My guests are expected to squint into the icy spray and put up with my shouting )

 

[rwoofer]

Not sure I buy the curved fins concept despite JFMs very thorough and initially convincing explanation. I can believe the side effects bit, but not the getting the better axis bit.

One way I like to test any theories I have is to extrapolate and see where that takes me. In this case I would extrapolate the curvature to 90 degrees and in that case the end of the fin would sweep through the water longitudinally and therefore provide no benefit at all. From that I would reason that even if you could argue that the angle of the vector is better, it would lose its intensity at a similar rate therefore undermining that overall benefit. I suspect that the net effect would therefore considerably less than you might expect with the logic that I think I understand from JFM.