Stabilizers: A Must for Passage-Making?

[long-cours.62]

One of the Dutch companies selling the Magnus rotors also sells a wing like you are talking about, mounted on or near the transom and horizontal. It is electrically controlled however.

Yes, I think I posted here a photo of boat fitted with that type of equipment...somewhere on this site but don't remember where ...

 

[Sweetypie]

It's amazing that so much effort and attention is placed on stabilization, while ignoring what almost every commercial fishing boat uses, which are called "rolling chocks" or bilge keels"

These simple, zero maintenance, relatively inexpensive, popular devices are for the most part ignored by the recreational boating community.

for $20,000 I changed my Bayliner from a rolly polly boat, into a stable boat in a beam sea.
I do not need to deploy anything.
I do not need to maintain anything.
They work equally well at anchor or underway.

The amplitude of my rolling is dramatically decreased.
The roll period is the same.
That results in much lower roll velocity, and much lower roll acceleration and deceleration, which is what people feel when a boat rolls.

Why do recreational boaters ignore this proven, popular, roll reduction technique?
Do we somehow need to make things difficult or complex for our minds to be satisfied?
Or is this just the result of our online, information available world, where we need to overanalyze things to the N th degree?

I can not answer for others, but for myself it's more about the creativity.
If my sole goal was to have a stable boat I would install a Gyro or buy a Multihull.

Rolling chocks absolutely would work to some degree, I am thinking more along the lines of creating a system that is simple, requires no electronics and can be lifted out of the water just like a wind vane (Self steering system used on blue water Yachts) this system is simple and requires no power to operate.

All concepts and ideas start with thinking outside the box a little and most of all not following the trends of normal.

I believe having stabilisers that act to counter the forces or a vessel rolling rather than just dampening the forces will have more of an effect.

I have only seen rolling chocks on 2 vessels here in Western Australia.

 

[Pascall]

Dutch ships are almost always equipped with bilge keels.
I think it's because Dutch ships are usually built of steel and it's very easy and cheap to install bilge keels.
Often the bilge keels are also used for cooling the engine and as a support to let the boat fall dry.

Greeting,

Pascal.

 

[long-cours.62]

https://no.yachtworld.com/yacht/1995-pieter-beeldsnijder-60-explorer-yacht-4187678/

 

[Hippocampus]

Read NASA and USN papers on motion sickness. There are people more sensitive to fast frequency motion and others slow. Some are intolerant of ships but not boats. Some are tolerant of ships and full displacement hulls but not multi hulls or planing boats. Tolerance varies but with the right stimulus anyone can get sick. I’m fortunate and resistant but did get sick when upside down fixing a stay from ama to ala while cold and overtired.
For moving around both speed, rhythm and amplitude of the motion are important for ability to function.
Most people are fairly resistant to motion in one axis. That rarely occurs on a small boat. You nearly always have some pitch, heave and roll. Most stabilizing techniques address only one parameter. In order to have decent impact that technique should ideally decrease that motion by 70% or better. In moderate conditions fins, fish and Magnus does exceed that value. Rolling chocks don’t. Definitely help but not as well as other measures. In a commercial application where cost is a major driving factor they make sense. There is no need to go recreational boating in any form. As percentage of total cost making the jump to more expensive techniques is more appealing.

 

[Mako]

Thanks for throwing some actual numbers down @Hippocampus.

From my research I’ve learned that the “average” rolling chock is rather worthless at less than 10% effectiveness.

The better designed, larger ones, like what KSanders has, are pushing about 35% reduction. That’s the maximum my naval architect claimed could be achieved. For our design he indicated a width of about 12-14 inches.

When I spoke with Dr Bass he stated the max reduction of a well-tuned flume tank is about 65%. My feeling is that a flume, coupled with a heavy chined hull, would be sufficient, especially because they work at anchor.

If one wants to achieve greater effectiveness then only active stabs of some type are required.

Now that my search has shifted heavily towards used vessels, I actually find that those with traditional hydraulic fins are a mixed blessing. That’s because they don’t work at anchor, which is an important use-case for my wife.

 

[long-cours.62]

Here may be not exactly the same %
https://www.kastenmarine.com/roll_attenuation.htm
On our Long-Cours 62 the add of our relatively short bilge Keel change a lot the roll and with mast and 17sqm main sail it was not the same boat , much, much more comfortable...and I sold her ! I am stupid...
And now the building cost ( if I don't speak about my ...age !) is so high we can't built a "new" hull for a next Long-Cours 62:-((

 

[rslifkin]

Now that my search has shifted heavily towards used vessels, I actually find that those with traditional hydraulic fins are a mixed blessing. That’s because they don’t work at anchor, which is an important use-case for my wife.

Many of the newer fin setups do work at anchor, but they still share an issue with gyros, etc. Powering it at anchor requires a decent bit of power and is likely to require a lot of generator runtime, if not constant (would be constant if you don't install an electrically driven hydraulic pump).

Personally, I prefer a passive option for use at anchor regardless of what other stabilization is on board.

 

[ksanders]

Thanks for throwing some actual numbers down @Hippocampus.

From my research I’ve learned that the “average” rolling chock is rather worthless at less than 10% effectiveness.

The better designed, larger ones, like what KSanders has, are pushing about 35% reduction. That’s the maximum my naval architect claimed could be achieved. For our design he indicated a width of about 12-14 inches.

When I spoke with Dr Bass he stated the max reduction of a well-tuned flume tank is about 65%. My feeling is that a flume, coupled with a heavy chined hull, would be sufficient, especially because they work at anchor.

If one wants to achieve greater effectiveness then only active stabs of some type are required.

Now that my search has shifted heavily towards used vessels, I actually find that those with traditional hydraulic fins are a mixed blessing. That’s because they don’t work at anchor, which is an important use-case for my wife.

What I see agrees with what you posted. Most people install undersized rolling chocks.
Mine are 12 inches wide X 24 feet long.

Yes, 35% sounds about right, I suppose, but I have no measurable data. I could either continue dreaming of the $75,000 system that was realistically never going to be installed, or I could spend a small fraction of that amount and get significant improvement. In doing do I changed my boat sufficiently that I can now avoid tacking for comfort in most reasonable conditions. That is huge! How many times do cruisers tack to make things more comfortable? All the time in reality. Also my boat is very stable at anchor, a huge change.

To me, for my non passagemaking boat, I was able to put the beam sea problem to rest and move on to other things to improve cruising life.

I do not leave port in larger seas now. I am simply more comfortable, and I travel a straight line to my destination, reducing my time making way.

 

[Mako]

Good point @rslifkin,

I’m not a big fan of paravanes, but it intriguing how some here have fitted flopper stoppers on small struts, deployed at anchor only.

If I recall, I believe Simi may have done so.

 

[rslifkin]

Good point @rslifkin,

I’m not a big fan of paravanes, but it intriguing how some here have fitted flopper stoppers on small struts, deployed at anchor only.

If I recall, I believe Simi may have done so.

Yes, quite a few people have done that. Even just hanging flopper stoppers from the spring cleats can be a significant improvement in comfort at anchor. I'm building a better setup for mine this winter, then once I try them out next year I'll see if it's worth adding poles or if they're making enough improvement without the poles. Even the orange cones help noticeably at anchor in many conditions given enough weight under them (they don't kill the roll, but they reduce it and damp it heavily, so it's slower and smoother, plus the boat stops rolling much faster after something gets it started.

 

[DDW]

"35% effectiveness" is a slippery figure. Roll has a bunch of parameters, amplitude, acceleration, jerk, and dampening to name four. They are very difficult to measure accurately.

My rolling chocks are similarly sized to KSanders, my cost to install was $4000. I attempted to measure the difference but it is not possible without sophisticated equipment, mainly due to the inability to duplicate seaway conditions. An alternative would be to do two-boat comparisons, I've tried to arrange that but have not been able to so far. Easier with active stabilizers that have an on-off button.

From what measurements I did do, the amplitude seems to be reduced only slightly, the acceleration and jerk more, and dampening most of all. It made a very noticeable difference in comfort. For the 5 or 10% of the cost of active roll stabilization, I thought they were well worth it, and would do them again if I changed boats without further thought.

 

[long-cours.62]

Just few problem with bilge keel it is the drag, the position and the form...
For example at 6kts and 8 or 10 kts the water do 't follow exactly the same hull line
Where put the " compromise" for the forme of Blige keel" stait , curved, how much ?

 

[ksanders]

Just few problem with bilge keel it is the drag, the position and the form...
For example at 6kts and 8 or 10 kts the water do 't follow exactly the same hull line
Where put the " compromise" for the forme of Blige keel" stait , curved, how much ?

The easiest way to do it is to run them straight down the waterline with the front and the back being the same distance from the waterline if you will

 

[Mako]

I’ve always read that short of actual tank or real-life testing, that they follow the diagonals

 

[ksanders]

if you run them along the waterline in a boat that is semi displacement, then they will have almost no drag at hull speed

If you speed up and your bow rises, theoretically, they would tend to add lift and in theory, they would add drag as well because any force needs an opposite force

 

[Mako]

makes sense, and my comment was in reference to displacement hulls of course