Seakeeper? Other things?

[Caballero II]

People still only mention 3 forms of stabilization. But Magnus effect devices.
Are immediate on/off.
Retract to lie flush against the hull
Work at all speeds including none
Continue to work at all heel angles and in any sea state.
Do not require hydraulics nor use large areas of internal space.
Do not have the big draw at start up of gyros.
Have been in use for decades so technology is well established
Work in forward and reverse.
Do not increase airdraft nor beam(when retracted)
Are of comparable cost to modern fins or gyros.
Are as effective in decreasing roll as gyros and like gyros more effective thean fish or fins.

If I was doing a new build I would consider them. Particularly as electric motor tech has improved in recent years.

Hippo, I thought I read they only work at speed, not at no speed. That their effectiveness is dependent on the inertia they develop as speed increases. Check that out. I could be wrong, but that was the reason I would consider them, but only if I could deploy flopper stoppers at anchor.

 

[Mambo42]

Hippo, I thought I read they only work at speed, not at no speed. That their effectiveness is dependent on the inertia they develop as speed increases. Check that out. I could be wrong, but that was the reason I would consider them, but only if I could deploy flopper stoppers at anchor.

Indeed, stabilizers based on the Magnus effect only work when there is waterflow over the stabilizers. Without flow they don't work. Basically they work according to the same principle as an aircraft wing, creating an under pressure on one side and an over pressure on the other side.
Humphree also works with a rotor system, but started to couple that to a fin system for zero speed. Why you would want to have both is a bit of a mystery to me.

DMS now also has a new system, which really looks impressive and am pretty sure it will function fine. However, I fear it will be expensive, but if money would not be an issue this would definitely be something to look into.

https://www.dmsholland.com/products...7e8rrWjz2NLPNBromQULE3eEk3yYF2skaAtjEEALw_wcB

 

[DDW]

There are Magnus rotor stabilizers that work at anchor. They generate the needed flow by "flapping", that is, moving the rotors through the water on their folding axis. Fins are the same, they only work when still by flapping. A gyro is the only thing equally as effective at any speed.

 

[Hippocampus]

Been looking at ice class designs. Having immersed stability devices being able to fold/retract seems necessary as they would strike chunk ice when deployed. Seems niaid and quantum both make fins that do that. In construction one can spec indents in the hull so there’s virtually no possibility the fins would suffer a strike. Believe given they rotate even with the boat still they can develop lift to prevent roll. Beyond ice classification could see retraction being worthwhile if frequency in skinny water with detritus such as logs or large branches. Have only been able to look at promo stuff but the quantum dyna foil device seems interesting.

 

[DDW]

If you are building a boat, the Magnus rotors would be easier to retract into a nacelle. They also retract when struck, not sure what retractable fins do, but seems unlikely that they would, as they would have to be guaranteed aligned with the well they go into.

 

[Mambo42]

There are Magnus rotor stabilizers that work at anchor. They generate the needed flow by "flapping", that is, moving the rotors through the water on their folding axis. Fins are the same, they only work when still by flapping. A gyro is the only thing equally as effective at any speed.

Normal Magnus rotors cannot work without waterflow, which means water needs to move over the rotor. Unless you are lying in an area with a lot of current your Magnus rotors are pretty useless.
The Magnus system that you are talking about is the system I put in the link of DMS. Those fins can flap like the wings of a bird and fold away when you don't need them. It is a beautiful system, top of the line, but a bit out of most people's budget.

Normal hydraulic fins need hydraulic power to operate, which means it needs an hydraulic pump and that is usually attached to an engine or a stand alone pump, but that uses a lot of electricity. Problem with hydraulic is that it cannot react as fast as an electrical motor. Zero speed performance of hydraulic fins is not going to be really good. On top of that, hydraulic fins cannot spin 360 degrees.

Electric fins are able to keep the boat fully stabilized (meaning roll stable, limited in pitch) while at anchor. The fins can induce a roll at zero speed, so that is basically what the system does, but then opposite and since an electric motor has almost no delay, the damping effect is instantaneous. The moment the control gyro detects a disturbance it sends a signal to the fins and they will react immediately, keeping the boat stable.
Of course the fins don't fold away, so yes, they will cause drag, just like any other fin system (or rotor system). You cannot go into an ice field, but I would not do that with any GRP boat to begin with.

A gyro can keep a boat indeed very stable, however the higher the speed the more difficult it becomes for a gyro. I.o.w. the faster you go with the boat the more heavy and faster spinning a gyro should be. And that uses up an enormous amount of energy (read: electricity).
If you have a boat with a high capacity generator, which is running 24/7 and you have amps to spare, then you can use a gyro. But for us it was no option since we don't have spare capacity on our generator and we don't want to run it 24/7.

 

[DDW]

Normal Magnus rotors cannot work without waterflow, which means water needs to move over the rotor. Unless you are lying in an area with a lot of current your Magnus rotors are pretty useless.

I will say it again, this time with feeling. There are Magnus rotor stabilizers that work at anchor with no current. Look for example at the Rotorswing products. These, like most Magnus rotor stabilizers, swing forward and aft on an axis perpendicular to the rotor. By swinging them when the boat is stationary, flow over the rotor is created. The claim is they are more effective than fins (which after all, just flap).

 

[Mambo42]

I will say it again, this time with feeling. There are Magnus rotor stabilizers that work at anchor with no current. Look for example at the Rotorswing products. These, like most Magnus rotor stabilizers, swing forward and aft on an axis perpendicular to the rotor. By swinging them when the boat is stationary, flow over the rotor is created. The claim is they are more effective than fins (which after all, just flap).

Also here the rotor is moved to create a waterflow. And that is exactly what fins do as well. There is absolutely no difference if you look at it from a basic point of view.

The rotor creates an under pressure on one side and an over pressure on the other side, thereby pushing the boat up or down.
Fins move rapidly through the water, just like a duck (or a bird or even a fish) uses its 'fins' to move itself through the water. Heck, even if you wear flippers when you are diving you are doing the same thing, you push yourself in a direction, which makes movement through the water more efficient.

And since I have electric fins and we are lying 100 % stable in the water at anchor I have no idea what can be more stable than 100 % stable ?

I had a video of our boat lying in the port of Symi (Greece), unfortunately lost it because of a stupid mistake I made with my phone. Wanted to post it on Instagram, but screwed it up.
It was end of October last year, evening, storm from the East, which meant waves were pushed into the port and at the same time a ferry came in. All the boats in that port were rocking and rolling violently (boats were slammed into the quay), people actually had to get off their boats or had to grab on to something to prevent them of being thrown around.
Next to us was a 70' to 80 ish Princess, charter boat. The guests had to get off the boat, otherwise they would get sea sick. I still remember the faces of the guests, being miserable, standing on the shore at night, not able to go back on board. They could not even walk on the passarelle, since that one was rolling along with the boat.
And at the same time our fins were working perfectly fine, we were lying steady as a rock, the only boat in the port that was not rolling. We could see the question marks on the faces of the guests of the charter boat next to us: 'why is our charter boat going bananas and why is the (smaller) boat, next to the charter boat, not moving at all ?

Would the Magnus be able to keep us stable at that time ?
Probably, but just one problem.........since they stick out next to the boat you cannot have any boats lying next to you. Our electric fins don't stick out, so we can use them in a port or marina with boats lying right next to us.

The way I see it this therefore is that the Magnus rotor is another way to create stability. Electricity plus computing power are able to do that.
The Magnus had a short coming (need to have moving water over the rotor) and thus they came up with this idea of moving the rotor arm. Clever way to solve the problem, but I fear this system will use more electricity since it not only has to power the rotor, but now also the movement of the whole rotor itself. Can you then still run them off the batteries ? I can't give you that answer.


In any case the instant reaction of an electric motor is the big advantage over hydraulic- and pneumatic stabilizers, however those are great when you have a larger vessel. The electric stabilization (gyro, rotor or fins) are (still) limited to a certain size boat. In time they will get bigger, but I don't see them being installed on a 300 mtr cruise ship. That will always be the realm of the hydraulic stabilizers.

 

[DDW]

The Magnus had a short coming (need to have moving water over the rotor) and thus they came up with this idea of moving the rotor arm.

Fins have exactly the same problem and exactly the same solution. I've no idea which uses more power, but can't see an obvious advantage (in power) for one vs. the other. Lying next to others the rotors could interfere, but I think operation while tied up in a marina is an unusual case for most.

I'm not trying to sell you Magnus rotors, just pointing out that there are versions that claim to work at zero boat speed.

 

[Mambo42]

Fins have exactly the same problem and exactly the same solution. I've no idea which uses more power, but can't see an obvious advantage (in power) for one vs. the other. Lying next to others the rotors could interfere, but I think operation while tied up in a marina is an unusual case for most.

I'm not trying to sell you Magnus rotors, just pointing out that there are versions that claim to work at zero boat speed.

The difference in power is that the Magnus has basically 2 motors to power. One for the rotor and the other one to move the arm. I don't know how much electricity each motor uses once it is operating, but the technical info sheet says it is about 1 Kw (220 V) while in operation (per rotor system). That is the motor to power the rotor.
Then we have the motor to move the arm of the rotor and I guess that is about the same as the motor that moves my fins, so that equals out.
I.o.w. I am guessing this system will use about 1 Kw extra while in operation and that is per rotor system.

Again, not a problem if you have a generator running all the time or while you are underway (alternator will provide the power), but at night, with no engine or generator running it could become a problem. Don't say it will, because it all depends on the sea state and the size of your battery bank.
I know I can run my fins off the battery bank all night long without having to fear draining the batteries.

In the end the type of stabilization is for everyone to decide. What do you require ? How do you run your boat and what are your priorities ?

My boat is, by nature, very unstable. Before we had the stabilizers we were rocking and rolling in the marina when waves would come in or when the wind would pick up. Our neighbors would be lying completely steady and we had to hold on for dear life. I had the bilge boards, but they did not help at all, so that gave me 2 choices: sell the boat and find something that was more stable or add stabilization.
Since we spend a lot of time on anchor I wanted a system that could perform while we were on the chain. Having the experience of rocking and rolling in a port or marina it would be great if we could get stabilized there as well.
And since I did not want to sleep with a generator running it needed to be a system that I can run off the batteries.

In the end I came to one conclusion and that was that electrical fins were the way to go. I found out who made them, started looking for reviews of owners, spoke with owners and thus arrived at the Stab 25. Took me about a year of research before I made the decision.
Since that time there have been more developments, but that is normal. Everything develops, there is no stopping that. So one day there will be a more efficient system, that uses less power or that can actually generate power while not in use for stabilization.
But for me that does not matter anymore, I am happy with what I have, it does the job and does it with very little electricity usage. For boats, in the size that most of us have, it is great that we have a solution which is usable when we don't have a lot of power available, doesn't take up too much space and gives us the level of comfort we all desire.

 

[Hippocampus]

Seems retractable fins are the most common system used for light ice class boats. Also the most common system used by the military. When retracted they are inside the boundaries of the hull so very unlikely to be injured even when in an ice field. The SKL version from Germany even offers a fin box cover. Reason isn’t to offer more protection but rather decrease drag by 90% when fin is fully retracted into its box. Can’t see energy requirements in order to compare Magnus to current versions of fin. All provide at rest stabilization. Magnus needs energy to do so. Would think fins when deployed but with no energy going in to them would still provide some roll resistance much like rolling chocks. Defer to those with more experience but with current self contained hydraulics on current fin systems much of the negatives have been decreased. Still much in electrics favor. Gyros, Magnus and fin can all be electrics. My SeaKeeper does draw a lot when spinning up. Seems to draw more as conditions worsen as well. Manual says one must expect that increase in draw. Don’t know to what degree the other systems draw increases as seastate worsens. Would guess Magnus effect devices would need to spin faster to give more roll resistance so would draw more as conditions deteriorated as well. Also don’t know relative efficiency of hydraulic v electric fins. Please educate.
Have wondered why one doesn’t use flopperstoppers when at rest and active stabilization when moving. Do see that set up on some boats. If done with forethought could have fish available if the active stabilization failed. Perhaps would need to be a bit more robust than usual flopperstoppers but not that much extra weight.

 

[Mambo42]

Seems retractable fins are the most common system used for light ice class boats. Also the most common system used by the military. When retracted they are inside the boundaries of the hull so very unlikely to be injured even when in an ice field. The SKL version from Germany even offers a fin box cover. Reason isn’t to offer more protection but rather decrease drag by 90% when fin is fully retracted into its box.

I agree with you that retractable fins will have less drag than fins that stay out, but am not sure that it would matter too much for the boats most of us are using.
Since that I have the fins I have noticed I need about 100 rpm extra (per engine) to get to the same speed as I had before (without fins). Obviously the fuel economy has gone down a bit, but as an added benefit we basically now have the stabilizers stand by, even when the sea is not that rough. As long as the sea remains calm they won't use up any energy, they will remain in neutral position. At the moment we are in the Aegean which is notorious for bad weather, but this summer we will be in Croatia where the seas are usually calm. Would be nice if we could fold them away. However, I have no idea what that would do for growth of barnicles etc ?

Can’t see energy requirements in order to compare Magnus to current versions of fin. All provide at rest stabilization. Magnus needs energy to do so. Would think fins when deployed but with no energy going in to them would still provide some roll resistance much like rolling chocks. Defer to those with more experience but with current self contained hydraulics on current fin systems much of the negatives have been decreased. Still much in electrics favor. Gyros, Magnus and fin can all be electrics.

Electric fins do need electricity to keep the boat stable while at anchor, but there is this neat feature on my fins, which is the sensitivity. By reducing the sensitivity the fins will not react to every little disturbance. The higher the sensitivity the more electricity it will use and the lower the sensitivity the less it will use.
In addition to that I have a night mode, which already reduces the electricity usage by 50 %. The way it does that is by moving the fins at a much lower speed, which means the roll dampening effect is still there, but not as fast.
When I then also put the sensitivity to minimum I reduce the electricity usage even further, since is not going to react to every little disturbance. And if it reacts, it reacts at a lower speed. In the end it means that the night time modes use as little as possible, but still provide adequate roll dampening. And if the sea would turn rough all of a sudden the fins will dampen the roll out completely, it just takes a bit longer, but then we are asleep and don't notice it (at least not me )

My SeaKeeper does draw a lot when spinning up. Seems to draw more as conditions worsen as well. Manual says one must expect that increase in draw. Don’t know to what degree the other systems draw increases as seastate worsens. Would guess Magnus effect devices would need to spin faster to give more roll resistance so would draw more as conditions deteriorated as well. Also don’t know relative efficiency of hydraulic v electric fins. Please educate.

The reason why a gyro needs more energy when the weather worsens is that the forces on the gyro basically act as friction (or resistance), which would slow the gyro down. In order to prevent that the motor has to increase power to keep the gyro spinning at the desired RPM.

If the weather worsens for us also our system will use more electricity and obviously at anchor it will use more electricity than underway. At anchor the fins are less efficient, therefore need larger deflections, therefore require more electricity.
Underway I usually see about 10 - 12 Amps (24 V) when they operate. Most I have seen was 40 - 45 Amps (24 V).
At anchor the total draw we normally have is about 5 - 10 amps (24 V) for a normal anchorage and 60 - 70 amps (24 V) when e.g. we had the storm plus the ferry in Symi (Greece). Good part there was that we were on shore power, so I could not care less how much they were using

Have wondered why one doesn’t use flopperstoppers when at rest and active stabilization when moving. Do see that set up on some boats. If done with forethought could have fish available if the active stabilization failed. Perhaps would need to be a bit more robust than usual flopperstoppers but not that much extra weight.

I thought about flopper stoppers and paravanes a lot. I wish I could have installed them on my boat, would have been a hell of a lot cheaper than the electric fins I have now. However, having no mast and being in Europe, where the majority has never heard of flopper stoppers or even paravanes, I knew I was in for a very difficult project. Building them myself was well beyond my capabilities. Adding a mast, booms and all the other equipment to make them work would be quite a challenge, so I decided against that.

Once I figured out that the electric fins would work on anchor and even in port, there was no need anymore for flopper stoppers. As soon as we come into an anchorage or in a port I place the fins in dock mode, put the sensitivity down to minimum and don't even think about them anymore. They will do their job, requiring no attention whatsoever and since I have enough solar and lithium battery capacity I don't worry about the amps they draw.
If I would have chosen hydraulic fins I most likely would have pursued the flopper stopper more seriously. Hydraulic fins on anchor is just a mismatch (at least for us) and then I would have wanted something like the flopper stopper. I think it works perfect for what we need, no electricity usage, not a lot can break down and simple to deploy.

A gyro will also work fine on anchor, will absolutely do the job, but for us the electricity draw was simply too much. I would not be able to run the gyro on solar and our battery pack and that made me decide to keep searching for a different solution.

 

[Jklotz]

I agree with you that retractable fins will have less drag than fins that stay out, but am not sure that it would matter too much for the boats most of us are using.
Since that I have the fins I have noticed I need about 100 rpm extra (per engine) to get to the same speed as I had before (without fins). Obviously the fuel economy has gone down a bit, but as an added benefit we basically now have the stabilizers stand by, even when the sea is not that rough. As long as the sea remains calm they won't use up any energy, they will remain in neutral position. At the moment we are in the Aegean which is notorious for bad weather, but this summer we will be in Croatia where the seas are usually calm. Would be nice if we could fold them away. However, I have no idea what that would do for growth of barnicles etc ?



Electric fins do need electricity to keep the boat stable while at anchor, but there is this neat feature on my fins, which is the sensitivity. By reducing the sensitivity the fins will not react to every little disturbance. The higher the sensitivity the more electricity it will use and the lower the sensitivity the less it will use.
In addition to that I have a night mode, which already reduces the electricity usage by 50 %. The way it does that is by moving the fins at a much lower speed, which means the roll dampening effect is still there, but not as fast.
When I then also put the sensitivity to minimum I reduce the electricity usage even further, since is not going to react to every little disturbance. And if it reacts, it reacts at a lower speed. In the end it means that the night time modes use as little as possible, but still provide adequate roll dampening. And if the sea would turn rough all of a sudden the fins will dampen the roll out completely, it just takes a bit longer, but then we are asleep and don't notice it (at least not me )


The reason why a gyro needs more energy when the weather worsens is that the forces on the gyro basically act as friction (or resistance), which would slow the gyro down. In order to prevent that the motor has to increase power to keep the gyro spinning at the desired RPM.

If the weather worsens for us also our system will use more electricity and obviously at anchor it will use more electricity than underway. At anchor the fins are less efficient, therefore need larger deflections, therefore require more electricity.
Underway I usually see about 10 - 12 Amps (24 V) when they operate. Most I have seen was 40 - 45 Amps (24 V).
At anchor the total draw we normally have is about 5 - 10 amps (24 V) for a normal anchorage and 60 - 70 amps (24 V) when e.g. we had the storm plus the ferry in Symi (Greece). Good part there was that we were on shore power, so I could not care less how much they were using



I thought about flopper stoppers and paravanes a lot. I wish I could have installed them on my boat, would have been a hell of a lot cheaper than the electric fins I have now. However, having no mast and being in Europe, where the majority has never heard of flopper stoppers or even paravanes, I knew I was in for a very difficult project. Building them myself was well beyond my capabilities. Adding a mast, booms and all the other equipment to make them work would be quite a challenge, so I decided against that.

Once I figured out that the electric fins would work on anchor and even in port, there was no need anymore for flopper stoppers. As soon as we come into an anchorage or in a port I place the fins in dock mode, put the sensitivity down to minimum and don't even think about them anymore. They will do their job, requiring no attention whatsoever and since I have enough solar and lithium battery capacity I don't worry about the amps they draw.
If I would have chosen hydraulic fins I most likely would have pursued the flopper stopper more seriously. Hydraulic fins on anchor is just a mismatch (at least for us) and then I would have wanted something like the flopper stopper. I think it works perfect for what we need, no electricity usage, not a lot can break down and simple to deploy.

A gyro will also work fine on anchor, will absolutely do the job, but for us the electricity draw was simply too much. I would not be able to run the gyro on solar and our battery pack and that made me decide to keep searching for a different solution.

What are the maintenance requirements like for your system?

 

[Mambo42]

What are the maintenance requirements like for your system?

The system will notify me after each 500 hrs. Then I will need to do what is called "self maintenance" and this basically is as follows:

1. clean the air filters of the control boxes (with a vacuum cleaner or just wash them).
2. check the torque on the bolts of the motors to the hull.
3. check for leakages.

After you have done that you have to enter the date you did the self test and that is it.

After 5000 hours or 2 years (whichever comes first) you need to change the outer seal of the motors. This means taking the fins off (8 bolts each) and then open the outer side of the motor, change the seal and close it again.
The outer seal is not connected to the inner side of the electrical motor, so no water can get there under any circumstance.

That maintenance should be done by a CMC service specialist and I will do that at the end of the season when the boat will come out for the winter. Most likely I will be well past the 5000 hours (probably have 7000 hours), but CMC has agreed it is no problem to wait until then.
According to CMC changing the seal can be done in a couple of hours and then I will be good again for another 5000 hours. In the end, what it will come down to for me is that I will simply change them each year at the end of the season. We spend 8 to 9 months per year on the boat, always have them on st by, so the hours count quickly for us.
For us it basically does not matter to change them at the end of the season. We take the boat out anyway, keep it on the dry during the winter months and put it back in the water in April. Much less hassle with monitoring the boat, just lock it down, leave it and be on our merry way.

I understand that, if you leave the boat in the water all year long, hauling out the boat every year can become costly. But then again, that only applies if you spend all year long on the boat and have the stabilizers on all year long. For others that could be (first time) after 2 years and then after 5000 hrs again.

And that is basically the only maintenance you will need to do. The system has a warranty of 2 years and I have spoken with captains of charter boats (have their systems on also continuously) and basically nobody reported any problems.

 

[Hippocampus]

Thanks Mambo. Would note any imperfection that disturbs laminar flow produces parasitic drag. Each through hull does as does your bow thruster even if faired. Racing sailboats use manifolds to decrease number of through hulls for that reason. So one would expect retractable fins or rotating Magnus cyclinders to produce some drag even when retracted. Agree probably much less than fixed fins or fish but some. It’s interesting one vendor offers a way to close the retraction box. I would expect once closed there’s minimal water flow and no light so growth would be minimal. Some vendors suggest their fixed fins produce enough vertical lift at speed as to increase efficiency. (Vector fins -Imtra). Wonder if Magnus which can be installed in a horizontal plane do this as well?
Our SeaKeeper has its lowest draw once spun up when we are at anchor. Still usually turn it off and the genset just before bed as like you don’t mind being rocked to sleep. If I had the opportunity would probably have a mixed system or several pairs of one type. Be so nice to impact on pitch as well as roll. My impression is most folks habituate to roll over time but few do habituate to corkscrewing motions. Guess we will always need to put up with heave unless we’re foiling but to get rid of two axis of movement would be so nice.

 

[Mambo42]

Found this video today about a Magnus Master installation in the US.

 

[Mambo42]

And in this video there are some under water shots of electric fins in action.